Patchwork [v6,3/4] block: add block timer and block throttling algorithm

login
register
mail settings
Submitter Zhi Yong Wu
Date Sept. 1, 2011, 11:44 a.m.
Message ID <1314877456-19521-4-git-send-email-wuzhy@linux.vnet.ibm.com>
Download mbox | patch
Permalink /patch/112900/
State New
Headers show

Comments

Zhi Yong Wu - Sept. 1, 2011, 11:44 a.m.
Note:
     1.) When bps/iops limits are specified to a small value such as 511 bytes/s, this VM will hang up. We are considering how to handle this senario.
     2.) When "dd" command is issued in guest, if its option bs is set to a large value such as "bs=1024K", the result speed will slightly bigger than the limits.

For these problems, if you have nice thought, pls let us know.:)

Signed-off-by: Zhi Yong Wu <wuzhy@linux.vnet.ibm.com>
---
 block.c     |  290 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++--
 block.h     |    5 +
 block_int.h |    9 ++
 3 files changed, 296 insertions(+), 8 deletions(-)
Stefan Hajnoczi - Sept. 1, 2011, 1:36 p.m.
On Thu, Sep 1, 2011 at 12:44 PM, Zhi Yong Wu <wuzhy@linux.vnet.ibm.com> wrote:
> Note:
>     1.) When bps/iops limits are specified to a small value such as 511 bytes/s, this VM will hang up. We are considering how to handle this senario.
>     2.) When "dd" command is issued in guest, if its option bs is set to a large value such as "bs=1024K", the result speed will slightly bigger than the limits.
>
> For these problems, if you have nice thought, pls let us know.:)
>
> Signed-off-by: Zhi Yong Wu <wuzhy@linux.vnet.ibm.com>
> ---
>  block.c     |  290 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++--
>  block.h     |    5 +
>  block_int.h |    9 ++
>  3 files changed, 296 insertions(+), 8 deletions(-)
>
> diff --git a/block.c b/block.c
> index 17ee3df..680f1e7 100644
> --- a/block.c
> +++ b/block.c
> @@ -30,6 +30,9 @@
>  #include "qemu-objects.h"
>  #include "qemu-coroutine.h"
>
> +#include "qemu-timer.h"
> +#include "block/blk-queue.h"
> +
>  #ifdef CONFIG_BSD
>  #include <sys/types.h>
>  #include <sys/stat.h>
> @@ -72,6 +75,13 @@ static int coroutine_fn bdrv_co_writev_em(BlockDriverState *bs,
>                                          QEMUIOVector *iov);
>  static int coroutine_fn bdrv_co_flush_em(BlockDriverState *bs);
>
> +static bool bdrv_exceed_bps_limits(BlockDriverState *bs, int nb_sectors,
> +        bool is_write, double elapsed_time, uint64_t *wait);
> +static bool bdrv_exceed_iops_limits(BlockDriverState *bs, bool is_write,
> +        double elapsed_time, uint64_t *wait);
> +static bool bdrv_exceed_io_limits(BlockDriverState *bs, int nb_sectors,
> +        bool is_write, uint64_t *wait);
> +
>  static QTAILQ_HEAD(, BlockDriverState) bdrv_states =
>     QTAILQ_HEAD_INITIALIZER(bdrv_states);
>
> @@ -104,6 +114,64 @@ int is_windows_drive(const char *filename)
>  }
>  #endif
>
> +/* throttling disk I/O limits */
> +void bdrv_io_limits_disable(BlockDriverState *bs)
> +{
> +    bs->io_limits_enabled = false;
> +
> +    if (bs->block_queue) {
> +        qemu_block_queue_flush(bs->block_queue);
> +        qemu_del_block_queue(bs->block_queue);
> +        bs->block_queue = NULL;
> +    }
> +
> +    if (bs->block_timer) {
> +        qemu_del_timer(bs->block_timer);
> +        qemu_free_timer(bs->block_timer);
> +        bs->block_timer = NULL;
> +    }
> +
> +    bs->slice_start[BLOCK_IO_LIMIT_READ]  = 0;
> +    bs->slice_start[BLOCK_IO_LIMIT_WRITE] = 0;
> +
> +    bs->slice_end[BLOCK_IO_LIMIT_READ]    = 0;
> +    bs->slice_end[BLOCK_IO_LIMIT_WRITE]   = 0;
> +}
> +
> +static void bdrv_block_timer(void *opaque)
> +{
> +    BlockDriverState *bs = opaque;
> +    BlockQueue *queue = bs->block_queue;
> +
> +    qemu_block_queue_flush(queue);
> +}
> +
> +void bdrv_io_limits_enable(BlockDriverState *bs)
> +{
> +    bs->block_queue    = qemu_new_block_queue();
> +    bs->block_timer    = qemu_new_timer_ns(vm_clock, bdrv_block_timer, bs);
> +
> +    bs->slice_start[BLOCK_IO_LIMIT_READ]  = qemu_get_clock_ns(vm_clock);
> +    bs->slice_start[BLOCK_IO_LIMIT_WRITE] =
> +           bs->slice_start[BLOCK_IO_LIMIT_READ];
> +
> +    bs->slice_end[BLOCK_IO_LIMIT_READ]    =
> +           bs->slice_start[BLOCK_IO_LIMIT_READ] + BLOCK_IO_SLICE_TIME;
> +    bs->slice_end[BLOCK_IO_LIMIT_WRITE]   =
> +           bs->slice_end[BLOCK_IO_LIMIT_READ];
> +}
> +
> +bool bdrv_io_limits_enabled(BlockDriverState *bs)
> +{
> +    BlockIOLimit *io_limits = &bs->io_limits;
> +    return io_limits->bps[BLOCK_IO_LIMIT_READ]
> +         || io_limits->bps[BLOCK_IO_LIMIT_WRITE]
> +         || io_limits->bps[BLOCK_IO_LIMIT_TOTAL]
> +         || io_limits->iops[BLOCK_IO_LIMIT_READ]
> +         || io_limits->iops[BLOCK_IO_LIMIT_WRITE]
> +         || io_limits->iops[BLOCK_IO_LIMIT_TOTAL];
> +}
> +
>  /* check if the path starts with "<protocol>:" */
>  static int path_has_protocol(const char *path)
>  {
> @@ -694,6 +762,11 @@ int bdrv_open(BlockDriverState *bs, const char *filename, int flags,
>             bs->change_cb(bs->change_opaque, CHANGE_MEDIA);
>     }
>
> +    /* throttling disk I/O limits */
> +    if (bs->io_limits_enabled) {
> +        bdrv_io_limits_enable(bs);
> +    }
> +
>     return 0;
>
>  unlink_and_fail:
> @@ -732,6 +805,18 @@ void bdrv_close(BlockDriverState *bs)
>         if (bs->change_cb)
>             bs->change_cb(bs->change_opaque, CHANGE_MEDIA);
>     }
> +
> +    /* throttling disk I/O limits */
> +    if (bs->block_queue) {
> +        qemu_del_block_queue(bs->block_queue);
> +        bs->block_queue = NULL;
> +    }
> +
> +    if (bs->block_timer) {
> +        qemu_del_timer(bs->block_timer);
> +        qemu_free_timer(bs->block_timer);
> +        bs->block_timer = NULL;
> +    }
>  }
>
>  void bdrv_close_all(void)
> @@ -2290,13 +2375,29 @@ BlockDriverAIOCB *bdrv_aio_readv(BlockDriverState *bs, int64_t sector_num,
>                                  BlockDriverCompletionFunc *cb, void *opaque)
>  {
>     BlockDriver *drv = bs->drv;
> +    uint64_t wait_time = 0;
> +    BlockDriverAIOCB *ret;
>
>     trace_bdrv_aio_readv(bs, sector_num, nb_sectors, opaque);
>
> -    if (!drv)
> -        return NULL;
> -    if (bdrv_check_request(bs, sector_num, nb_sectors))
> +    if (!drv || bdrv_check_request(bs, sector_num, nb_sectors)) {
>         return NULL;
> +    }
> +
> +    /* throttling disk read I/O */
> +    if (bs->io_limits_enabled) {
> +        if (bdrv_exceed_io_limits(bs, nb_sectors, false, &wait_time)) {
> +            ret = qemu_block_queue_enqueue(bs->block_queue, bs, bdrv_aio_readv,
> +                           sector_num, qiov, nb_sectors, cb, opaque);
> +            qemu_mod_timer(bs->block_timer,
> +                           wait_time + qemu_get_clock_ns(vm_clock));
> +            return ret;
> +        }
> +
> +        bs->io_disps.bytes[BLOCK_IO_LIMIT_READ] +=
> +                           (unsigned) nb_sectors * BDRV_SECTOR_SIZE;
> +        bs->io_disps.ios[BLOCK_IO_LIMIT_READ]++;
> +    }
>
>     return drv->bdrv_aio_readv(bs, sector_num, qiov, nb_sectors,
>                                cb, opaque);
> @@ -2345,15 +2446,14 @@ BlockDriverAIOCB *bdrv_aio_writev(BlockDriverState *bs, int64_t sector_num,
>     BlockDriver *drv = bs->drv;
>     BlockDriverAIOCB *ret;
>     BlockCompleteData *blk_cb_data;
> +    uint64_t wait_time = 0;
>
>     trace_bdrv_aio_writev(bs, sector_num, nb_sectors, opaque);
>
> -    if (!drv)
> -        return NULL;
> -    if (bs->read_only)
> -        return NULL;
> -    if (bdrv_check_request(bs, sector_num, nb_sectors))
> +    if (!drv || bs->read_only
> +        || bdrv_check_request(bs, sector_num, nb_sectors)) {
>         return NULL;
> +    }
>
>     if (bs->dirty_bitmap) {
>         blk_cb_data = blk_dirty_cb_alloc(bs, sector_num, nb_sectors, cb,
> @@ -2362,6 +2462,17 @@ BlockDriverAIOCB *bdrv_aio_writev(BlockDriverState *bs, int64_t sector_num,
>         opaque = blk_cb_data;
>     }
>
> +    /* throttling disk write I/O */
> +    if (bs->io_limits_enabled) {
> +        if (bdrv_exceed_io_limits(bs, nb_sectors, true, &wait_time)) {
> +            ret = qemu_block_queue_enqueue(bs->block_queue, bs, bdrv_aio_writev,
> +                                  sector_num, qiov, nb_sectors, cb, opaque);
> +            qemu_mod_timer(bs->block_timer,
> +                                  wait_time + qemu_get_clock_ns(vm_clock));
> +            return ret;
> +        }
> +    }
> +
>     ret = drv->bdrv_aio_writev(bs, sector_num, qiov, nb_sectors,
>                                cb, opaque);
>
> @@ -2369,6 +2480,12 @@ BlockDriverAIOCB *bdrv_aio_writev(BlockDriverState *bs, int64_t sector_num,
>         if (bs->wr_highest_sector < sector_num + nb_sectors - 1) {
>             bs->wr_highest_sector = sector_num + nb_sectors - 1;
>         }
> +
> +        if (bs->io_limits_enabled) {
> +            bs->io_disps.bytes[BLOCK_IO_LIMIT_WRITE] +=
> +                               (unsigned) nb_sectors * BDRV_SECTOR_SIZE;
> +            bs->io_disps.ios[BLOCK_IO_LIMIT_WRITE]++;
> +        }
>     }
>
>     return ret;
> @@ -2633,6 +2750,163 @@ void bdrv_aio_cancel(BlockDriverAIOCB *acb)
>     acb->pool->cancel(acb);
>  }
>
> +static bool bdrv_exceed_bps_limits(BlockDriverState *bs, int nb_sectors,
> +                 bool is_write, double elapsed_time, uint64_t *wait) {
> +    uint64_t bps_limit = 0;
> +    double   bytes_limit, bytes_disp, bytes_res;
> +    double   slice_time, wait_time;
> +
> +    if (bs->io_limits.bps[BLOCK_IO_LIMIT_TOTAL]) {
> +        bps_limit = bs->io_limits.bps[BLOCK_IO_LIMIT_TOTAL];
> +    } else if (bs->io_limits.bps[is_write]) {
> +        bps_limit = bs->io_limits.bps[is_write];
> +    } else {
> +        if (wait) {
> +            *wait = 0;
> +        }
> +
> +        return false;
> +    }
> +
> +    slice_time = bs->slice_end[is_write] - bs->slice_start[is_write];
> +    slice_time /= (NANOSECONDS_PER_SECOND);
> +    bytes_limit = bps_limit * slice_time;
> +    bytes_disp  = bs->io_disps.bytes[is_write];
> +    if (bs->io_limits.bps[BLOCK_IO_LIMIT_TOTAL]) {
> +        bytes_disp += bs->io_disps.bytes[!is_write];
> +    }
> +
> +    bytes_res   = (unsigned) nb_sectors * BDRV_SECTOR_SIZE;
> +
> +    if (bytes_disp + bytes_res <= bytes_limit) {
> +        if (wait) {
> +            *wait = 0;
> +        }
> +
> +        return false;
> +    }
> +
> +    /* Calc approx time to dispatch */
> +    wait_time = (bytes_disp + bytes_res) / bps_limit - elapsed_time;
> +
> +    if (wait) {
> +        *wait = wait_time * BLOCK_IO_SLICE_TIME * 10;
> +    }
> +
> +    return true;
> +}
> +
> +static bool bdrv_exceed_iops_limits(BlockDriverState *bs, bool is_write,
> +                             double elapsed_time, uint64_t *wait) {
> +    uint64_t iops_limit = 0;
> +    double   ios_limit, ios_disp;
> +    double   slice_time, wait_time;
> +
> +    if (bs->io_limits.iops[BLOCK_IO_LIMIT_TOTAL]) {
> +        iops_limit = bs->io_limits.iops[BLOCK_IO_LIMIT_TOTAL];
> +    } else if (bs->io_limits.iops[is_write]) {
> +        iops_limit = bs->io_limits.iops[is_write];
> +    } else {
> +        if (wait) {
> +            *wait = 0;
> +        }
> +
> +        return false;
> +    }
> +
> +    slice_time = bs->slice_end[is_write] - bs->slice_start[is_write];
> +    slice_time /= (NANOSECONDS_PER_SECOND);
> +    ios_limit  = iops_limit * slice_time;
> +    ios_disp   = bs->io_disps.ios[is_write];
> +    if (bs->io_limits.iops[BLOCK_IO_LIMIT_TOTAL]) {
> +        ios_disp += bs->io_disps.ios[!is_write];
> +    }
> +
> +    if (ios_disp + 1 <= ios_limit) {
> +        if (wait) {
> +            *wait = 0;
> +        }
> +
> +        return false;
> +    }
> +
> +    /* Calc approx time to dispatch */
> +    wait_time = (ios_disp + 1) / iops_limit;
> +    if (wait_time > elapsed_time) {
> +        wait_time = wait_time - elapsed_time;
> +    } else {
> +        wait_time = 0;
> +    }
> +
> +    if (wait) {
> +        *wait = wait_time * BLOCK_IO_SLICE_TIME * 10;
> +    }
> +
> +    return true;
> +}
> +
> +static bool bdrv_exceed_io_limits(BlockDriverState *bs, int nb_sectors,
> +                           bool is_write, uint64_t *wait) {
> +    int64_t  now;
> +    uint64_t bps_wait = 0, iops_wait = 0, max_wait;
> +    double   elapsed_time;
> +    int      bps_ret, iops_ret;
> +
> +    now = qemu_get_clock_ns(vm_clock);
> +    if ((bs->slice_start[is_write] < now)
> +        && (bs->slice_end[is_write] > now)) {
> +        bs->slice_end[is_write]   = now + BLOCK_IO_SLICE_TIME;
> +    } else {
> +        bs->slice_start[is_write]     = now;
> +        bs->slice_end[is_write]       = now + BLOCK_IO_SLICE_TIME;
> +
> +        bs->io_disps.bytes[is_write]  = 0;
> +        bs->io_disps.bytes[!is_write] = 0;
> +
> +        bs->io_disps.ios[is_write]    = 0;
> +        bs->io_disps.ios[!is_write]   = 0;

Does it make sense to keep separate slice_start/slice_end for read and
write since we reset the dispatched statistics to zero for both?
Perhaps we should use a scalar slice_start/slice_end and not two
separate values for read/write.

> +    }
> +
> +    /* If a limit was exceeded, immediately queue this request */
> +    if (qemu_block_queue_has_pending(bs->block_queue)) {
> +        if (bs->io_limits.bps[BLOCK_IO_LIMIT_TOTAL]
> +            || bs->io_limits.bps[is_write] || bs->io_limits.iops[is_write]
> +            || bs->io_limits.iops[BLOCK_IO_LIMIT_TOTAL]) {
> +            if (wait) {
> +                *wait = 0;

This causes the queue to be flushed each time the guest enqueues an
I/O while there are queued requests.  Perhaps this is (part of) the
CPU overhead that Ryan's benchmarking discovered.

If we try to preserve request ordering then I don't think there is a
reason to modify the timer once it has been set.

Stefan
Zhi Yong Wu - Sept. 5, 2011, 7:10 a.m.
On Thu, Sep 01, 2011 at 02:36:41PM +0100, Stefan Hajnoczi wrote:
>Date: Thu, 1 Sep 2011 14:36:41 +0100
>Message-ID: <CAJSP0QU8GqWsA6jaYAfs0=hvabQayfRPSzRNctGP6GEGgptHaw@mail.gmail.com>
>From: Stefan Hajnoczi <stefanha@gmail.com>
>To: Zhi Yong Wu <wuzhy@linux.vnet.ibm.com>
>Content-Type: text/plain; charset=ISO-8859-1
>Content-Transfer-Encoding: quoted-printable
>X-detected-operating-system: by eggs.gnu.org: GNU/Linux 2.6 (newer, 2)
>X-Received-From: 209.85.216.45
>Cc: kwolf@redhat.com, aliguori@us.ibm.com, stefanha@linux.vnet.ibm.com,
> kvm@vger.kernel.org, mtosatti@redhat.com, qemu-devel@nongnu.org,
> pair@us.ibm.com, zwu.kernel@gmail.com, ryanh@us.ibm.com
>Subject: Re: [Qemu-devel] [PATCH v6 3/4] block: add block timer and block
> throttling algorithm
>X-BeenThere: qemu-devel@nongnu.org
>X-Mailman-Version: 2.1.14
>Precedence: list
>List-Id: <qemu-devel.nongnu.org>
>List-Unsubscribe: <https://lists.nongnu.org/mailman/options/qemu-devel>,
> <mailto:qemu-devel-request@nongnu.org?subject=unsubscribe>
>List-Archive: </archive/html/qemu-devel>
>List-Post: <mailto:qemu-devel@nongnu.org>
>List-Help: <mailto:qemu-devel-request@nongnu.org?subject=help>
>List-Subscribe: <https://lists.nongnu.org/mailman/listinfo/qemu-devel>,
> <mailto:qemu-devel-request@nongnu.org?subject=subscribe>
>X-Mailman-Copy: yes
>Errors-To: qemu-devel-bounces+wuzhy=linux.vnet.ibm.com@nongnu.org
>Sender: qemu-devel-bounces+wuzhy=linux.vnet.ibm.com@nongnu.org
>X-Brightmail-Tracker: AAAAAA==
>X-Xagent-From: stefanha@gmail.com
>X-Xagent-To: wuzhy@linux.vnet.ibm.com
>X-Xagent-Gateway: bldgate.vnet.ibm.com (XAGENTU8 at BLDGATE)
>
>On Thu, Sep 1, 2011 at 12:44 PM, Zhi Yong Wu <wuzhy@linux.vnet.ibm.com> wrote:
>> Note:
>>     1.) When bps/iops limits are specified to a small value such as 511 bytes/s, this VM will hang up. We are considering how to handle this senario.
>>     2.) When "dd" command is issued in guest, if its option bs is set to a large value such as "bs=1024K", the result speed will slightly bigger than the limits.
>>
>> For these problems, if you have nice thought, pls let us know.:)
>>
>> Signed-off-by: Zhi Yong Wu <wuzhy@linux.vnet.ibm.com>
>> ---
>>  block.c     |  290 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++--
>>  block.h     |    5 +
>>  block_int.h |    9 ++
>>  3 files changed, 296 insertions(+), 8 deletions(-)
>>
>> diff --git a/block.c b/block.c
>> index 17ee3df..680f1e7 100644
>> --- a/block.c
>> +++ b/block.c
>> @@ -30,6 +30,9 @@
>>  #include "qemu-objects.h"
>>  #include "qemu-coroutine.h"
>>
>> +#include "qemu-timer.h"
>> +#include "block/blk-queue.h"
>> +
>>  #ifdef CONFIG_BSD
>>  #include <sys/types.h>
>>  #include <sys/stat.h>
>> @@ -72,6 +75,13 @@ static int coroutine_fn bdrv_co_writev_em(BlockDriverState *bs,
>>                                          QEMUIOVector *iov);
>>  static int coroutine_fn bdrv_co_flush_em(BlockDriverState *bs);
>>
>> +static bool bdrv_exceed_bps_limits(BlockDriverState *bs, int nb_sectors,
>> +        bool is_write, double elapsed_time, uint64_t *wait);
>> +static bool bdrv_exceed_iops_limits(BlockDriverState *bs, bool is_write,
>> +        double elapsed_time, uint64_t *wait);
>> +static bool bdrv_exceed_io_limits(BlockDriverState *bs, int nb_sectors,
>> +        bool is_write, uint64_t *wait);
>> +
>>  static QTAILQ_HEAD(, BlockDriverState) bdrv_states =
>>     QTAILQ_HEAD_INITIALIZER(bdrv_states);
>>
>> @@ -104,6 +114,64 @@ int is_windows_drive(const char *filename)
>>  }
>>  #endif
>>
>> +/* throttling disk I/O limits */
>> +void bdrv_io_limits_disable(BlockDriverState *bs)
>> +{
>> +    bs->io_limits_enabled = false;
>> +
>> +    if (bs->block_queue) {
>> +        qemu_block_queue_flush(bs->block_queue);
>> +        qemu_del_block_queue(bs->block_queue);
>> +        bs->block_queue = NULL;
>> +    }
>> +
>> +    if (bs->block_timer) {
>> +        qemu_del_timer(bs->block_timer);
>> +        qemu_free_timer(bs->block_timer);
>> +        bs->block_timer = NULL;
>> +    }
>> +
>> +    bs->slice_start[BLOCK_IO_LIMIT_READ]  = 0;
>> +    bs->slice_start[BLOCK_IO_LIMIT_WRITE] = 0;
>> +
>> +    bs->slice_end[BLOCK_IO_LIMIT_READ]    = 0;
>> +    bs->slice_end[BLOCK_IO_LIMIT_WRITE]   = 0;
>> +}
>> +
>> +static void bdrv_block_timer(void *opaque)
>> +{
>> +    BlockDriverState *bs = opaque;
>> +    BlockQueue *queue = bs->block_queue;
>> +
>> +    qemu_block_queue_flush(queue);
>> +}
>> +
>> +void bdrv_io_limits_enable(BlockDriverState *bs)
>> +{
>> +    bs->block_queue    = qemu_new_block_queue();
>> +    bs->block_timer    = qemu_new_timer_ns(vm_clock, bdrv_block_timer, bs);
>> +
>> +    bs->slice_start[BLOCK_IO_LIMIT_READ]  = qemu_get_clock_ns(vm_clock);
>> +    bs->slice_start[BLOCK_IO_LIMIT_WRITE] =
>> +           bs->slice_start[BLOCK_IO_LIMIT_READ];
>> +
>> +    bs->slice_end[BLOCK_IO_LIMIT_READ]    =
>> +           bs->slice_start[BLOCK_IO_LIMIT_READ] + BLOCK_IO_SLICE_TIME;
>> +    bs->slice_end[BLOCK_IO_LIMIT_WRITE]   =
>> +           bs->slice_end[BLOCK_IO_LIMIT_READ];
>> +}
>> +
>> +bool bdrv_io_limits_enabled(BlockDriverState *bs)
>> +{
>> +    BlockIOLimit *io_limits = &bs->io_limits;
>> +    return io_limits->bps[BLOCK_IO_LIMIT_READ]
>> +         || io_limits->bps[BLOCK_IO_LIMIT_WRITE]
>> +         || io_limits->bps[BLOCK_IO_LIMIT_TOTAL]
>> +         || io_limits->iops[BLOCK_IO_LIMIT_READ]
>> +         || io_limits->iops[BLOCK_IO_LIMIT_WRITE]
>> +         || io_limits->iops[BLOCK_IO_LIMIT_TOTAL];
>> +}
>> +
>>  /* check if the path starts with "<protocol>:" */
>>  static int path_has_protocol(const char *path)
>>  {
>> @@ -694,6 +762,11 @@ int bdrv_open(BlockDriverState *bs, const char *filename, int flags,
>>             bs->change_cb(bs->change_opaque, CHANGE_MEDIA);
>>     }
>>
>> +    /* throttling disk I/O limits */
>> +    if (bs->io_limits_enabled) {
>> +        bdrv_io_limits_enable(bs);
>> +    }
>> +
>>     return 0;
>>
>>  unlink_and_fail:
>> @@ -732,6 +805,18 @@ void bdrv_close(BlockDriverState *bs)
>>         if (bs->change_cb)
>>             bs->change_cb(bs->change_opaque, CHANGE_MEDIA);
>>     }
>> +
>> +    /* throttling disk I/O limits */
>> +    if (bs->block_queue) {
>> +        qemu_del_block_queue(bs->block_queue);
>> +        bs->block_queue = NULL;
>> +    }
>> +
>> +    if (bs->block_timer) {
>> +        qemu_del_timer(bs->block_timer);
>> +        qemu_free_timer(bs->block_timer);
>> +        bs->block_timer = NULL;
>> +    }
>>  }
>>
>>  void bdrv_close_all(void)
>> @@ -2290,13 +2375,29 @@ BlockDriverAIOCB *bdrv_aio_readv(BlockDriverState *bs, int64_t sector_num,
>>                                  BlockDriverCompletionFunc *cb, void *opaque)
>>  {
>>     BlockDriver *drv = bs->drv;
>> +    uint64_t wait_time = 0;
>> +    BlockDriverAIOCB *ret;
>>
>>     trace_bdrv_aio_readv(bs, sector_num, nb_sectors, opaque);
>>
>> -    if (!drv)
>> -        return NULL;
>> -    if (bdrv_check_request(bs, sector_num, nb_sectors))
>> +    if (!drv || bdrv_check_request(bs, sector_num, nb_sectors)) {
>>         return NULL;
>> +    }
>> +
>> +    /* throttling disk read I/O */
>> +    if (bs->io_limits_enabled) {
>> +        if (bdrv_exceed_io_limits(bs, nb_sectors, false, &wait_time)) {
>> +            ret = qemu_block_queue_enqueue(bs->block_queue, bs, bdrv_aio_readv,
>> +                           sector_num, qiov, nb_sectors, cb, opaque);
>> +            qemu_mod_timer(bs->block_timer,
>> +                           wait_time + qemu_get_clock_ns(vm_clock));
>> +            return ret;
>> +        }
>> +
>> +        bs->io_disps.bytes[BLOCK_IO_LIMIT_READ] +=
>> +                           (unsigned) nb_sectors * BDRV_SECTOR_SIZE;
>> +        bs->io_disps.ios[BLOCK_IO_LIMIT_READ]++;
>> +    }
>>
>>     return drv->bdrv_aio_readv(bs, sector_num, qiov, nb_sectors,
>>                                cb, opaque);
>> @@ -2345,15 +2446,14 @@ BlockDriverAIOCB *bdrv_aio_writev(BlockDriverState *bs, int64_t sector_num,
>>     BlockDriver *drv = bs->drv;
>>     BlockDriverAIOCB *ret;
>>     BlockCompleteData *blk_cb_data;
>> +    uint64_t wait_time = 0;
>>
>>     trace_bdrv_aio_writev(bs, sector_num, nb_sectors, opaque);
>>
>> -    if (!drv)
>> -        return NULL;
>> -    if (bs->read_only)
>> -        return NULL;
>> -    if (bdrv_check_request(bs, sector_num, nb_sectors))
>> +    if (!drv || bs->read_only
>> +        || bdrv_check_request(bs, sector_num, nb_sectors)) {
>>         return NULL;
>> +    }
>>
>>     if (bs->dirty_bitmap) {
>>         blk_cb_data = blk_dirty_cb_alloc(bs, sector_num, nb_sectors, cb,
>> @@ -2362,6 +2462,17 @@ BlockDriverAIOCB *bdrv_aio_writev(BlockDriverState *bs, int64_t sector_num,
>>         opaque = blk_cb_data;
>>     }
>>
>> +    /* throttling disk write I/O */
>> +    if (bs->io_limits_enabled) {
>> +        if (bdrv_exceed_io_limits(bs, nb_sectors, true, &wait_time)) {
>> +            ret = qemu_block_queue_enqueue(bs->block_queue, bs, bdrv_aio_writev,
>> +                                  sector_num, qiov, nb_sectors, cb, opaque);
>> +            qemu_mod_timer(bs->block_timer,
>> +                                  wait_time + qemu_get_clock_ns(vm_clock));
>> +            return ret;
>> +        }
>> +    }
>> +
>>     ret = drv->bdrv_aio_writev(bs, sector_num, qiov, nb_sectors,
>>                                cb, opaque);
>>
>> @@ -2369,6 +2480,12 @@ BlockDriverAIOCB *bdrv_aio_writev(BlockDriverState *bs, int64_t sector_num,
>>         if (bs->wr_highest_sector < sector_num + nb_sectors - 1) {
>>             bs->wr_highest_sector = sector_num + nb_sectors - 1;
>>         }
>> +
>> +        if (bs->io_limits_enabled) {
>> +            bs->io_disps.bytes[BLOCK_IO_LIMIT_WRITE] +=
>> +                               (unsigned) nb_sectors * BDRV_SECTOR_SIZE;
>> +            bs->io_disps.ios[BLOCK_IO_LIMIT_WRITE]++;
>> +        }
>>     }
>>
>>     return ret;
>> @@ -2633,6 +2750,163 @@ void bdrv_aio_cancel(BlockDriverAIOCB *acb)
>>     acb->pool->cancel(acb);
>>  }
>>
>> +static bool bdrv_exceed_bps_limits(BlockDriverState *bs, int nb_sectors,
>> +                 bool is_write, double elapsed_time, uint64_t *wait) {
>> +    uint64_t bps_limit = 0;
>> +    double   bytes_limit, bytes_disp, bytes_res;
>> +    double   slice_time, wait_time;
>> +
>> +    if (bs->io_limits.bps[BLOCK_IO_LIMIT_TOTAL]) {
>> +        bps_limit = bs->io_limits.bps[BLOCK_IO_LIMIT_TOTAL];
>> +    } else if (bs->io_limits.bps[is_write]) {
>> +        bps_limit = bs->io_limits.bps[is_write];
>> +    } else {
>> +        if (wait) {
>> +            *wait = 0;
>> +        }
>> +
>> +        return false;
>> +    }
>> +
>> +    slice_time = bs->slice_end[is_write] - bs->slice_start[is_write];
>> +    slice_time /= (NANOSECONDS_PER_SECOND);
>> +    bytes_limit = bps_limit * slice_time;
>> +    bytes_disp  = bs->io_disps.bytes[is_write];
>> +    if (bs->io_limits.bps[BLOCK_IO_LIMIT_TOTAL]) {
>> +        bytes_disp += bs->io_disps.bytes[!is_write];
>> +    }
>> +
>> +    bytes_res   = (unsigned) nb_sectors * BDRV_SECTOR_SIZE;
>> +
>> +    if (bytes_disp + bytes_res <= bytes_limit) {
>> +        if (wait) {
>> +            *wait = 0;
>> +        }
>> +
>> +        return false;
>> +    }
>> +
>> +    /* Calc approx time to dispatch */
>> +    wait_time = (bytes_disp + bytes_res) / bps_limit - elapsed_time;
>> +
>> +    if (wait) {
>> +        *wait = wait_time * BLOCK_IO_SLICE_TIME * 10;
>> +    }
>> +
>> +    return true;
>> +}
>> +
>> +static bool bdrv_exceed_iops_limits(BlockDriverState *bs, bool is_write,
>> +                             double elapsed_time, uint64_t *wait) {
>> +    uint64_t iops_limit = 0;
>> +    double   ios_limit, ios_disp;
>> +    double   slice_time, wait_time;
>> +
>> +    if (bs->io_limits.iops[BLOCK_IO_LIMIT_TOTAL]) {
>> +        iops_limit = bs->io_limits.iops[BLOCK_IO_LIMIT_TOTAL];
>> +    } else if (bs->io_limits.iops[is_write]) {
>> +        iops_limit = bs->io_limits.iops[is_write];
>> +    } else {
>> +        if (wait) {
>> +            *wait = 0;
>> +        }
>> +
>> +        return false;
>> +    }
>> +
>> +    slice_time = bs->slice_end[is_write] - bs->slice_start[is_write];
>> +    slice_time /= (NANOSECONDS_PER_SECOND);
>> +    ios_limit  = iops_limit * slice_time;
>> +    ios_disp   = bs->io_disps.ios[is_write];
>> +    if (bs->io_limits.iops[BLOCK_IO_LIMIT_TOTAL]) {
>> +        ios_disp += bs->io_disps.ios[!is_write];
>> +    }
>> +
>> +    if (ios_disp + 1 <= ios_limit) {
>> +        if (wait) {
>> +            *wait = 0;
>> +        }
>> +
>> +        return false;
>> +    }
>> +
>> +    /* Calc approx time to dispatch */
>> +    wait_time = (ios_disp + 1) / iops_limit;
>> +    if (wait_time > elapsed_time) {
>> +        wait_time = wait_time - elapsed_time;
>> +    } else {
>> +        wait_time = 0;
>> +    }
>> +
>> +    if (wait) {
>> +        *wait = wait_time * BLOCK_IO_SLICE_TIME * 10;
>> +    }
>> +
>> +    return true;
>> +}
>> +
>> +static bool bdrv_exceed_io_limits(BlockDriverState *bs, int nb_sectors,
>> +                           bool is_write, uint64_t *wait) {
>> +    int64_t  now;
>> +    uint64_t bps_wait = 0, iops_wait = 0, max_wait;
>> +    double   elapsed_time;
>> +    int      bps_ret, iops_ret;
>> +
>> +    now = qemu_get_clock_ns(vm_clock);
>> +    if ((bs->slice_start[is_write] < now)
>> +        && (bs->slice_end[is_write] > now)) {
>> +        bs->slice_end[is_write]   = now + BLOCK_IO_SLICE_TIME;
>> +    } else {
>> +        bs->slice_start[is_write]     = now;
>> +        bs->slice_end[is_write]       = now + BLOCK_IO_SLICE_TIME;
>> +
>> +        bs->io_disps.bytes[is_write]  = 0;
>> +        bs->io_disps.bytes[!is_write] = 0;
>> +
>> +        bs->io_disps.ios[is_write]    = 0;
>> +        bs->io_disps.ios[!is_write]   = 0;
>
>Does it make sense to keep separate slice_start/slice_end for read and
>write since we reset the dispatched statistics to zero for both?
>Perhaps we should use a scalar slice_start/slice_end and not two
>separate values for read/write.
Right, currently the scalar slice_* should be adopted, thanks.
>
>> +    }
>> +
>> +    /* If a limit was exceeded, immediately queue this request */
>> +    if (qemu_block_queue_has_pending(bs->block_queue)) {
>> +        if (bs->io_limits.bps[BLOCK_IO_LIMIT_TOTAL]
>> +            || bs->io_limits.bps[is_write] || bs->io_limits.iops[is_write]
>> +            || bs->io_limits.iops[BLOCK_IO_LIMIT_TOTAL]) {
>> +            if (wait) {
>> +                *wait = 0;
>
>This causes the queue to be flushed each time the guest enqueues an
>I/O while there are queued requests.  Perhaps this is (part of) the
>CPU overhead that Ryan's benchmarking discovered.
>
>If we try to preserve request ordering then I don't think there is a
>reason to modify the timer once it has been set.
good catch, pls check the latest changes on my public git branch.

>
>Stefan
>

Patch

diff --git a/block.c b/block.c
index 17ee3df..680f1e7 100644
--- a/block.c
+++ b/block.c
@@ -30,6 +30,9 @@ 
 #include "qemu-objects.h"
 #include "qemu-coroutine.h"
 
+#include "qemu-timer.h"
+#include "block/blk-queue.h"
+
 #ifdef CONFIG_BSD
 #include <sys/types.h>
 #include <sys/stat.h>
@@ -72,6 +75,13 @@  static int coroutine_fn bdrv_co_writev_em(BlockDriverState *bs,
                                          QEMUIOVector *iov);
 static int coroutine_fn bdrv_co_flush_em(BlockDriverState *bs);
 
+static bool bdrv_exceed_bps_limits(BlockDriverState *bs, int nb_sectors,
+        bool is_write, double elapsed_time, uint64_t *wait);
+static bool bdrv_exceed_iops_limits(BlockDriverState *bs, bool is_write,
+        double elapsed_time, uint64_t *wait);
+static bool bdrv_exceed_io_limits(BlockDriverState *bs, int nb_sectors,
+        bool is_write, uint64_t *wait);
+
 static QTAILQ_HEAD(, BlockDriverState) bdrv_states =
     QTAILQ_HEAD_INITIALIZER(bdrv_states);
 
@@ -104,6 +114,64 @@  int is_windows_drive(const char *filename)
 }
 #endif
 
+/* throttling disk I/O limits */
+void bdrv_io_limits_disable(BlockDriverState *bs)
+{
+    bs->io_limits_enabled = false;
+
+    if (bs->block_queue) {
+        qemu_block_queue_flush(bs->block_queue);
+        qemu_del_block_queue(bs->block_queue);
+        bs->block_queue = NULL;
+    }
+
+    if (bs->block_timer) {
+        qemu_del_timer(bs->block_timer);
+        qemu_free_timer(bs->block_timer);
+        bs->block_timer = NULL;
+    }
+
+    bs->slice_start[BLOCK_IO_LIMIT_READ]  = 0;
+    bs->slice_start[BLOCK_IO_LIMIT_WRITE] = 0;
+
+    bs->slice_end[BLOCK_IO_LIMIT_READ]    = 0;
+    bs->slice_end[BLOCK_IO_LIMIT_WRITE]   = 0;
+}
+
+static void bdrv_block_timer(void *opaque)
+{
+    BlockDriverState *bs = opaque;
+    BlockQueue *queue = bs->block_queue;
+
+    qemu_block_queue_flush(queue);
+}
+
+void bdrv_io_limits_enable(BlockDriverState *bs)
+{
+    bs->block_queue    = qemu_new_block_queue();
+    bs->block_timer    = qemu_new_timer_ns(vm_clock, bdrv_block_timer, bs);
+
+    bs->slice_start[BLOCK_IO_LIMIT_READ]  = qemu_get_clock_ns(vm_clock);
+    bs->slice_start[BLOCK_IO_LIMIT_WRITE] =
+           bs->slice_start[BLOCK_IO_LIMIT_READ];
+
+    bs->slice_end[BLOCK_IO_LIMIT_READ]    =
+           bs->slice_start[BLOCK_IO_LIMIT_READ] + BLOCK_IO_SLICE_TIME;
+    bs->slice_end[BLOCK_IO_LIMIT_WRITE]   =
+           bs->slice_end[BLOCK_IO_LIMIT_READ];
+}
+
+bool bdrv_io_limits_enabled(BlockDriverState *bs)
+{
+    BlockIOLimit *io_limits = &bs->io_limits;
+    return io_limits->bps[BLOCK_IO_LIMIT_READ]
+         || io_limits->bps[BLOCK_IO_LIMIT_WRITE]
+         || io_limits->bps[BLOCK_IO_LIMIT_TOTAL]
+         || io_limits->iops[BLOCK_IO_LIMIT_READ]
+         || io_limits->iops[BLOCK_IO_LIMIT_WRITE]
+         || io_limits->iops[BLOCK_IO_LIMIT_TOTAL];
+}
+
 /* check if the path starts with "<protocol>:" */
 static int path_has_protocol(const char *path)
 {
@@ -694,6 +762,11 @@  int bdrv_open(BlockDriverState *bs, const char *filename, int flags,
             bs->change_cb(bs->change_opaque, CHANGE_MEDIA);
     }
 
+    /* throttling disk I/O limits */
+    if (bs->io_limits_enabled) {
+        bdrv_io_limits_enable(bs);
+    }
+
     return 0;
 
 unlink_and_fail:
@@ -732,6 +805,18 @@  void bdrv_close(BlockDriverState *bs)
         if (bs->change_cb)
             bs->change_cb(bs->change_opaque, CHANGE_MEDIA);
     }
+
+    /* throttling disk I/O limits */
+    if (bs->block_queue) {
+        qemu_del_block_queue(bs->block_queue);
+        bs->block_queue = NULL;
+    }
+
+    if (bs->block_timer) {
+        qemu_del_timer(bs->block_timer);
+        qemu_free_timer(bs->block_timer);
+        bs->block_timer = NULL;
+    }
 }
 
 void bdrv_close_all(void)
@@ -2290,13 +2375,29 @@  BlockDriverAIOCB *bdrv_aio_readv(BlockDriverState *bs, int64_t sector_num,
                                  BlockDriverCompletionFunc *cb, void *opaque)
 {
     BlockDriver *drv = bs->drv;
+    uint64_t wait_time = 0;
+    BlockDriverAIOCB *ret;
 
     trace_bdrv_aio_readv(bs, sector_num, nb_sectors, opaque);
 
-    if (!drv)
-        return NULL;
-    if (bdrv_check_request(bs, sector_num, nb_sectors))
+    if (!drv || bdrv_check_request(bs, sector_num, nb_sectors)) {
         return NULL;
+    }
+
+    /* throttling disk read I/O */
+    if (bs->io_limits_enabled) {
+        if (bdrv_exceed_io_limits(bs, nb_sectors, false, &wait_time)) {
+            ret = qemu_block_queue_enqueue(bs->block_queue, bs, bdrv_aio_readv,
+                           sector_num, qiov, nb_sectors, cb, opaque);
+            qemu_mod_timer(bs->block_timer,
+                           wait_time + qemu_get_clock_ns(vm_clock));
+            return ret;
+        }
+
+        bs->io_disps.bytes[BLOCK_IO_LIMIT_READ] +=
+                           (unsigned) nb_sectors * BDRV_SECTOR_SIZE;
+        bs->io_disps.ios[BLOCK_IO_LIMIT_READ]++;
+    }
 
     return drv->bdrv_aio_readv(bs, sector_num, qiov, nb_sectors,
                                cb, opaque);
@@ -2345,15 +2446,14 @@  BlockDriverAIOCB *bdrv_aio_writev(BlockDriverState *bs, int64_t sector_num,
     BlockDriver *drv = bs->drv;
     BlockDriverAIOCB *ret;
     BlockCompleteData *blk_cb_data;
+    uint64_t wait_time = 0;
 
     trace_bdrv_aio_writev(bs, sector_num, nb_sectors, opaque);
 
-    if (!drv)
-        return NULL;
-    if (bs->read_only)
-        return NULL;
-    if (bdrv_check_request(bs, sector_num, nb_sectors))
+    if (!drv || bs->read_only
+        || bdrv_check_request(bs, sector_num, nb_sectors)) {
         return NULL;
+    }
 
     if (bs->dirty_bitmap) {
         blk_cb_data = blk_dirty_cb_alloc(bs, sector_num, nb_sectors, cb,
@@ -2362,6 +2462,17 @@  BlockDriverAIOCB *bdrv_aio_writev(BlockDriverState *bs, int64_t sector_num,
         opaque = blk_cb_data;
     }
 
+    /* throttling disk write I/O */
+    if (bs->io_limits_enabled) {
+        if (bdrv_exceed_io_limits(bs, nb_sectors, true, &wait_time)) {
+            ret = qemu_block_queue_enqueue(bs->block_queue, bs, bdrv_aio_writev,
+                                  sector_num, qiov, nb_sectors, cb, opaque);
+            qemu_mod_timer(bs->block_timer,
+                                  wait_time + qemu_get_clock_ns(vm_clock));
+            return ret;
+        }
+    }
+
     ret = drv->bdrv_aio_writev(bs, sector_num, qiov, nb_sectors,
                                cb, opaque);
 
@@ -2369,6 +2480,12 @@  BlockDriverAIOCB *bdrv_aio_writev(BlockDriverState *bs, int64_t sector_num,
         if (bs->wr_highest_sector < sector_num + nb_sectors - 1) {
             bs->wr_highest_sector = sector_num + nb_sectors - 1;
         }
+
+        if (bs->io_limits_enabled) {
+            bs->io_disps.bytes[BLOCK_IO_LIMIT_WRITE] +=
+                               (unsigned) nb_sectors * BDRV_SECTOR_SIZE;
+            bs->io_disps.ios[BLOCK_IO_LIMIT_WRITE]++;
+        }
     }
 
     return ret;
@@ -2633,6 +2750,163 @@  void bdrv_aio_cancel(BlockDriverAIOCB *acb)
     acb->pool->cancel(acb);
 }
 
+static bool bdrv_exceed_bps_limits(BlockDriverState *bs, int nb_sectors,
+                 bool is_write, double elapsed_time, uint64_t *wait) {
+    uint64_t bps_limit = 0;
+    double   bytes_limit, bytes_disp, bytes_res;
+    double   slice_time, wait_time;
+
+    if (bs->io_limits.bps[BLOCK_IO_LIMIT_TOTAL]) {
+        bps_limit = bs->io_limits.bps[BLOCK_IO_LIMIT_TOTAL];
+    } else if (bs->io_limits.bps[is_write]) {
+        bps_limit = bs->io_limits.bps[is_write];
+    } else {
+        if (wait) {
+            *wait = 0;
+        }
+
+        return false;
+    }
+
+    slice_time = bs->slice_end[is_write] - bs->slice_start[is_write];
+    slice_time /= (NANOSECONDS_PER_SECOND);
+    bytes_limit = bps_limit * slice_time;
+    bytes_disp  = bs->io_disps.bytes[is_write];
+    if (bs->io_limits.bps[BLOCK_IO_LIMIT_TOTAL]) {
+        bytes_disp += bs->io_disps.bytes[!is_write];
+    }
+
+    bytes_res   = (unsigned) nb_sectors * BDRV_SECTOR_SIZE;
+
+    if (bytes_disp + bytes_res <= bytes_limit) {
+        if (wait) {
+            *wait = 0;
+        }
+
+        return false;
+    }
+
+    /* Calc approx time to dispatch */
+    wait_time = (bytes_disp + bytes_res) / bps_limit - elapsed_time;
+
+    if (wait) {
+        *wait = wait_time * BLOCK_IO_SLICE_TIME * 10;
+    }
+
+    return true;
+}
+
+static bool bdrv_exceed_iops_limits(BlockDriverState *bs, bool is_write,
+                             double elapsed_time, uint64_t *wait) {
+    uint64_t iops_limit = 0;
+    double   ios_limit, ios_disp;
+    double   slice_time, wait_time;
+
+    if (bs->io_limits.iops[BLOCK_IO_LIMIT_TOTAL]) {
+        iops_limit = bs->io_limits.iops[BLOCK_IO_LIMIT_TOTAL];
+    } else if (bs->io_limits.iops[is_write]) {
+        iops_limit = bs->io_limits.iops[is_write];
+    } else {
+        if (wait) {
+            *wait = 0;
+        }
+
+        return false;
+    }
+
+    slice_time = bs->slice_end[is_write] - bs->slice_start[is_write];
+    slice_time /= (NANOSECONDS_PER_SECOND);
+    ios_limit  = iops_limit * slice_time;
+    ios_disp   = bs->io_disps.ios[is_write];
+    if (bs->io_limits.iops[BLOCK_IO_LIMIT_TOTAL]) {
+        ios_disp += bs->io_disps.ios[!is_write];
+    }
+
+    if (ios_disp + 1 <= ios_limit) {
+        if (wait) {
+            *wait = 0;
+        }
+
+        return false;
+    }
+
+    /* Calc approx time to dispatch */
+    wait_time = (ios_disp + 1) / iops_limit;
+    if (wait_time > elapsed_time) {
+        wait_time = wait_time - elapsed_time;
+    } else {
+        wait_time = 0;
+    }
+
+    if (wait) {
+        *wait = wait_time * BLOCK_IO_SLICE_TIME * 10;
+    }
+
+    return true;
+}
+
+static bool bdrv_exceed_io_limits(BlockDriverState *bs, int nb_sectors,
+                           bool is_write, uint64_t *wait) {
+    int64_t  now;
+    uint64_t bps_wait = 0, iops_wait = 0, max_wait;
+    double   elapsed_time;
+    int      bps_ret, iops_ret;
+
+    now = qemu_get_clock_ns(vm_clock);
+    if ((bs->slice_start[is_write] < now)
+        && (bs->slice_end[is_write] > now)) {
+        bs->slice_end[is_write]   = now + BLOCK_IO_SLICE_TIME;
+    } else {
+        bs->slice_start[is_write]     = now;
+        bs->slice_end[is_write]       = now + BLOCK_IO_SLICE_TIME;
+
+        bs->io_disps.bytes[is_write]  = 0;
+        bs->io_disps.bytes[!is_write] = 0;
+
+        bs->io_disps.ios[is_write]    = 0;
+        bs->io_disps.ios[!is_write]   = 0;
+    }
+
+    /* If a limit was exceeded, immediately queue this request */
+    if (qemu_block_queue_has_pending(bs->block_queue)) {
+        if (bs->io_limits.bps[BLOCK_IO_LIMIT_TOTAL]
+            || bs->io_limits.bps[is_write] || bs->io_limits.iops[is_write]
+            || bs->io_limits.iops[BLOCK_IO_LIMIT_TOTAL]) {
+            if (wait) {
+                *wait = 0;
+            }
+
+            return true;
+        }
+    }
+
+    elapsed_time  = now - bs->slice_start[is_write];
+    elapsed_time  /= (NANOSECONDS_PER_SECOND);
+
+    bps_ret  = bdrv_exceed_bps_limits(bs, nb_sectors,
+                                      is_write, elapsed_time, &bps_wait);
+    iops_ret = bdrv_exceed_iops_limits(bs, is_write,
+                                      elapsed_time, &iops_wait);
+    if (bps_ret || iops_ret) {
+        max_wait = bps_wait > iops_wait ? bps_wait : iops_wait;
+        if (wait) {
+            *wait = max_wait;
+        }
+
+        now = qemu_get_clock_ns(vm_clock);
+        if (bs->slice_end[is_write] < now + max_wait) {
+            bs->slice_end[is_write] = now + max_wait;
+        }
+
+        return true;
+    }
+
+    if (wait) {
+        *wait = 0;
+    }
+
+    return false;
+}
 
 /**************************************************************/
 /* async block device emulation */
diff --git a/block.h b/block.h
index 3ac0b94..a3e69db 100644
--- a/block.h
+++ b/block.h
@@ -58,6 +58,11 @@  void bdrv_info(Monitor *mon, QObject **ret_data);
 void bdrv_stats_print(Monitor *mon, const QObject *data);
 void bdrv_info_stats(Monitor *mon, QObject **ret_data);
 
+/* disk I/O throttling */
+void bdrv_io_limits_enable(BlockDriverState *bs);
+void bdrv_io_limits_disable(BlockDriverState *bs);
+bool bdrv_io_limits_enabled(BlockDriverState *bs);
+
 void bdrv_init(void);
 void bdrv_init_with_whitelist(void);
 BlockDriver *bdrv_find_protocol(const char *filename);
diff --git a/block_int.h b/block_int.h
index e7bda5b..5d37277 100644
--- a/block_int.h
+++ b/block_int.h
@@ -202,6 +202,15 @@  struct BlockDriverState {
 
     void *sync_aiocb;
 
+    /* the time for latest disk I/O */
+    int64_t slice_start[2];
+    int64_t slice_end[2];
+    BlockIOLimit io_limits;
+    BlockIODisp  io_disps;
+    BlockQueue   *block_queue;
+    QEMUTimer    *block_timer;
+    bool         io_limits_enabled;
+
     /* I/O stats (display with "info blockstats"). */
     uint64_t nr_bytes[BDRV_MAX_IOTYPE];
     uint64_t nr_ops[BDRV_MAX_IOTYPE];