diff mbox

[v2] block/null: Latency simulation by adding new option "latency_ns"

Message ID 1425519178-17863-1-git-send-email-famz@redhat.com
State New
Headers show

Commit Message

Fam Zheng March 5, 2015, 1:32 a.m. UTC 
Aio context switch should just work because the requests will be
drained, so the scheduled timer(s) on the old context will be freed.

Signed-off-by: Fam Zheng <famz@redhat.com>

---
v2: Check for negative value; add sleep in null-co://. [Kevin]
---
 block/null.c | 55 ++++++++++++++++++++++++++++++++++++++++++++++++++-----
 1 file changed, 50 insertions(+), 5 deletions(-)

Comments

Eric Blake March 6, 2015, 5:14 p.m. UTC | #1 
On 03/04/2015 06:32 PM, Fam Zheng wrote:
> Aio context switch should just work because the requests will be
> drained, so the scheduled timer(s) on the old context will be freed.
> 
> Signed-off-by: Fam Zheng <famz@redhat.com>
> 
> ---
> v2: Check for negative value; add sleep in null-co://. [Kevin]
> ---
>  block/null.c | 55 ++++++++++++++++++++++++++++++++++++++++++++++++++-----
>  1 file changed, 50 insertions(+), 5 deletions(-)

Is it possible to pass this new parameter via QMP?  If so, shouldn't the
.json file also document it?  And if so, should it be named with '-'
instead of '_' for use from QMP?
Fam Zheng March 11, 2015, 5:16 a.m. UTC | #2 
On Fri, 03/06 10:14, Eric Blake wrote:
> On 03/04/2015 06:32 PM, Fam Zheng wrote:
> > Aio context switch should just work because the requests will be
> > drained, so the scheduled timer(s) on the old context will be freed.
> > 
> > Signed-off-by: Fam Zheng <famz@redhat.com>
> > 
> > ---
> > v2: Check for negative value; add sleep in null-co://. [Kevin]
> > ---
> >  block/null.c | 55 ++++++++++++++++++++++++++++++++++++++++++++++++++-----
> >  1 file changed, 50 insertions(+), 5 deletions(-)
> 
> Is it possible to pass this new parameter via QMP?  If so, shouldn't the
> .json file also document it?  And if so, should it be named with '-'
> instead of '_' for use from QMP?

Sure.

Fam
diff mbox

Patch

diff --git a/block/null.c b/block/null.c
index ec2bd27..7091164 100644
--- a/block/null.c
+++ b/block/null.c
@@ -12,8 +12,11 @@ 
 
 #include "block/block_int.h"
 
+#define NULL_OPT_LATENCY "latency_ns"
+
 typedef struct {
     int64_t length;
+    int64_t latency_ns;
 } BDRVNullState;
 
 static QemuOptsList runtime_opts = {
@@ -30,6 +33,12 @@  static QemuOptsList runtime_opts = {
             .type = QEMU_OPT_SIZE,
             .help = "size of the null block",
         },
+        {
+            .name = NULL_OPT_LATENCY,
+            .type = QEMU_OPT_NUMBER,
+            .help = "nanoseconds (approximated) to wait "
+                    "before completing request",
+        },
         { /* end of list */ }
     },
 };
@@ -44,6 +53,11 @@  static int null_file_open(BlockDriverState *bs, QDict *options, int flags,
     qemu_opts_absorb_qdict(opts, options, &error_abort);
     s->length =
         qemu_opt_get_size(opts, BLOCK_OPT_SIZE, 1 << 30);
+    s->latency_ns =
+        qemu_opt_get_number(opts, NULL_OPT_LATENCY, 0);
+    if (s->latency_ns < 0) {
+        error_setg(errp, "latency_ns is invalid");
+    }
     qemu_opts_del(opts);
     return 0;
 }
@@ -58,28 +72,41 @@  static int64_t null_getlength(BlockDriverState *bs)
     return s->length;
 }
 
+static coroutine_fn int null_co_common(BlockDriverState *bs)
+{
+    BDRVNullState *s = bs->opaque;
+
+    /* Only emulate latency after vcpu is running. */
+    if (s->latency_ns && qemu_clock_get_us(QEMU_CLOCK_VIRTUAL) > 0) {
+        co_aio_sleep_ns(bdrv_get_aio_context(bs), QEMU_CLOCK_VIRTUAL,
+                        s->latency_ns);
+    }
+    return 0;
+}
+
 static coroutine_fn int null_co_readv(BlockDriverState *bs,
                                       int64_t sector_num, int nb_sectors,
                                       QEMUIOVector *qiov)
 {
-    return 0;
+    return null_co_common(bs);
 }
 
 static coroutine_fn int null_co_writev(BlockDriverState *bs,
                                        int64_t sector_num, int nb_sectors,
                                        QEMUIOVector *qiov)
 {
-    return 0;
+    return null_co_common(bs);
 }
 
 static coroutine_fn int null_co_flush(BlockDriverState *bs)
 {
-    return 0;
+    return null_co_common(bs);
 }
 
 typedef struct {
     BlockAIOCB common;
     QEMUBH *bh;
+    QEMUTimer timer;
 } NullAIOCB;
 
 static const AIOCBInfo null_aiocb_info = {
@@ -94,15 +121,33 @@  static void null_bh_cb(void *opaque)
     qemu_aio_unref(acb);
 }
 
+static void null_timer_cb(void *opaque)
+{
+    NullAIOCB *acb = opaque;
+    acb->common.cb(acb->common.opaque, 0);
+    timer_deinit(&acb->timer);
+    qemu_aio_unref(acb);
+}
+
 static inline BlockAIOCB *null_aio_common(BlockDriverState *bs,
                                           BlockCompletionFunc *cb,
                                           void *opaque)
 {
     NullAIOCB *acb;
+    BDRVNullState *s = bs->opaque;
 
     acb = qemu_aio_get(&null_aiocb_info, bs, cb, opaque);
-    acb->bh = aio_bh_new(bdrv_get_aio_context(bs), null_bh_cb, acb);
-    qemu_bh_schedule(acb->bh);
+    /* Only emulate latency after vcpu is running. */
+    if (s->latency_ns && qemu_clock_get_us(QEMU_CLOCK_VIRTUAL) > 0) {
+        aio_timer_init(bdrv_get_aio_context(bs), &acb->timer,
+                       QEMU_CLOCK_VIRTUAL, SCALE_NS,
+                       null_timer_cb, acb);
+        timer_mod_ns(&acb->timer,
+                     qemu_clock_get_ns(QEMU_CLOCK_VIRTUAL) + s->latency_ns);
+    } else {
+        acb->bh = aio_bh_new(bdrv_get_aio_context(bs), null_bh_cb, acb);
+        qemu_bh_schedule(acb->bh);
+    }
     return &acb->common;
 }