| Message ID | 1371210243-6099-2-git-send-email-stefanha@redhat.com |
|---|---|
| State | New |
| Headers | show |
Il 14/06/2013 13:43, Stefan Hajnoczi ha scritto: > If a block driver has no file descriptors to monitor but there are still > active requests, it can return 1 from .io_flush(). This is used to spin > during synchronous I/O. > > Stop relying on .io_flush() and instead check > QLIST_EMPTY(&bs->tracked_requests) to decide whether there are active > requests. > > This is the first step in removing .io_flush() so that event loops no > longer need to have the concept of synchronous I/O. Eventually we may > be able to kill synchronous I/O completely by running everything in a > coroutine, but that is future work. > > Note this patch moves bs->throttled_reqs initialization to bdrv_new() so > that bdrv_requests_pending(bs) can safely access it. In practice bs is > g_malloc0() so the memory is already zeroed but it's safer to initialize > the queue properly. > > In bdrv_delete() make sure to call bdrv_make_anon() *after* bdrv_close() > so that the device is still seen by bdrv_drain_all() when iterating > bdrv_states. I wonder if this last change should be separated out and CCed to qemu-stable. It seems like a bug if you close a device that has pending throttled operations. Paolo > Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com> > --- > block.c | 50 +++++++++++++++++++++++++++++++++++++------------- > 1 file changed, 37 insertions(+), 13 deletions(-) > > diff --git a/block.c b/block.c > index 79ad33d..04821d8 100644 > --- a/block.c > +++ b/block.c > @@ -148,7 +148,6 @@ static void bdrv_block_timer(void *opaque) > > void bdrv_io_limits_enable(BlockDriverState *bs) > { > - qemu_co_queue_init(&bs->throttled_reqs); > bs->block_timer = qemu_new_timer_ns(vm_clock, bdrv_block_timer, bs); > bs->io_limits_enabled = true; > } > @@ -305,6 +304,7 @@ BlockDriverState *bdrv_new(const char *device_name) > } > bdrv_iostatus_disable(bs); > notifier_list_init(&bs->close_notifiers); > + qemu_co_queue_init(&bs->throttled_reqs); > > return bs; > } > @@ -1412,6 +1412,35 @@ void bdrv_close_all(void) > } > } > > +/* Check if any requests are in-flight (including throttled requests) */ > +static bool bdrv_requests_pending(BlockDriverState *bs) > +{ > + if (!QLIST_EMPTY(&bs->tracked_requests)) { > + return true; > + } > + if (!qemu_co_queue_empty(&bs->throttled_reqs)) { > + return true; > + } > + if (bs->file && bdrv_requests_pending(bs->file)) { > + return true; > + } > + if (bs->backing_hd && bdrv_requests_pending(bs->backing_hd)) { > + return true; > + } > + return false; > +} > + > +static bool bdrv_requests_pending_all(void) > +{ > + BlockDriverState *bs; > + QTAILQ_FOREACH(bs, &bdrv_states, list) { > + if (bdrv_requests_pending(bs)) { > + return true; > + } > + } > + return false; > +} > + > /* > * Wait for pending requests to complete across all BlockDriverStates > * > @@ -1426,27 +1455,22 @@ void bdrv_close_all(void) > */ > void bdrv_drain_all(void) > { > + /* Always run first iteration so any pending completion BHs run */ > + bool busy = true; > BlockDriverState *bs; > - bool busy; > - > - do { > - busy = qemu_aio_wait(); > > + while (busy) { > /* FIXME: We do not have timer support here, so this is effectively > * a busy wait. > */ > QTAILQ_FOREACH(bs, &bdrv_states, list) { > if (!qemu_co_queue_empty(&bs->throttled_reqs)) { > qemu_co_queue_restart_all(&bs->throttled_reqs); > - busy = true; > } > } > - } while (busy); > > - /* If requests are still pending there is a bug somewhere */ > - QTAILQ_FOREACH(bs, &bdrv_states, list) { > - assert(QLIST_EMPTY(&bs->tracked_requests)); > - assert(qemu_co_queue_empty(&bs->throttled_reqs)); > + busy = bdrv_requests_pending_all(); > + busy |= aio_poll(qemu_get_aio_context(), busy); > } > } > > @@ -1591,11 +1615,11 @@ void bdrv_delete(BlockDriverState *bs) > assert(!bs->job); > assert(!bs->in_use); > > + bdrv_close(bs); > + > /* remove from list, if necessary */ > bdrv_make_anon(bs); > > - bdrv_close(bs); > - > g_free(bs); > } > >
On Thu, Jun 27, 2013 at 03:13:19PM +0200, Paolo Bonzini wrote: > Il 14/06/2013 13:43, Stefan Hajnoczi ha scritto: > > If a block driver has no file descriptors to monitor but there are still > > active requests, it can return 1 from .io_flush(). This is used to spin > > during synchronous I/O. > > > > Stop relying on .io_flush() and instead check > > QLIST_EMPTY(&bs->tracked_requests) to decide whether there are active > > requests. > > > > This is the first step in removing .io_flush() so that event loops no > > longer need to have the concept of synchronous I/O. Eventually we may > > be able to kill synchronous I/O completely by running everything in a > > coroutine, but that is future work. > > > > Note this patch moves bs->throttled_reqs initialization to bdrv_new() so > > that bdrv_requests_pending(bs) can safely access it. In practice bs is > > g_malloc0() so the memory is already zeroed but it's safer to initialize > > the queue properly. > > > > In bdrv_delete() make sure to call bdrv_make_anon() *after* bdrv_close() > > so that the device is still seen by bdrv_drain_all() when iterating > > bdrv_states. > > I wonder if this last change should be separated out and CCed to > qemu-stable. It seems like a bug if you close a device that has pending > throttled operations. Seems like a good idea. I'll send the next version with a separated Cc: qemu-stable@nongnu.org patch. Stefan
diff --git a/block.c b/block.c index 79ad33d..04821d8 100644 --- a/block.c +++ b/block.c @@ -148,7 +148,6 @@ static void bdrv_block_timer(void *opaque) void bdrv_io_limits_enable(BlockDriverState *bs) { - qemu_co_queue_init(&bs->throttled_reqs); bs->block_timer = qemu_new_timer_ns(vm_clock, bdrv_block_timer, bs); bs->io_limits_enabled = true; } @@ -305,6 +304,7 @@ BlockDriverState *bdrv_new(const char *device_name) } bdrv_iostatus_disable(bs); notifier_list_init(&bs->close_notifiers); + qemu_co_queue_init(&bs->throttled_reqs); return bs; } @@ -1412,6 +1412,35 @@ void bdrv_close_all(void) } } +/* Check if any requests are in-flight (including throttled requests) */ +static bool bdrv_requests_pending(BlockDriverState *bs) +{ + if (!QLIST_EMPTY(&bs->tracked_requests)) { + return true; + } + if (!qemu_co_queue_empty(&bs->throttled_reqs)) { + return true; + } + if (bs->file && bdrv_requests_pending(bs->file)) { + return true; + } + if (bs->backing_hd && bdrv_requests_pending(bs->backing_hd)) { + return true; + } + return false; +} + +static bool bdrv_requests_pending_all(void) +{ + BlockDriverState *bs; + QTAILQ_FOREACH(bs, &bdrv_states, list) { + if (bdrv_requests_pending(bs)) { + return true; + } + } + return false; +} + /* * Wait for pending requests to complete across all BlockDriverStates * @@ -1426,27 +1455,22 @@ void bdrv_close_all(void) */ void bdrv_drain_all(void) { + /* Always run first iteration so any pending completion BHs run */ + bool busy = true; BlockDriverState *bs; - bool busy; - - do { - busy = qemu_aio_wait(); + while (busy) { /* FIXME: We do not have timer support here, so this is effectively * a busy wait. */ QTAILQ_FOREACH(bs, &bdrv_states, list) { if (!qemu_co_queue_empty(&bs->throttled_reqs)) { qemu_co_queue_restart_all(&bs->throttled_reqs); - busy = true; } } - } while (busy); - /* If requests are still pending there is a bug somewhere */ - QTAILQ_FOREACH(bs, &bdrv_states, list) { - assert(QLIST_EMPTY(&bs->tracked_requests)); - assert(qemu_co_queue_empty(&bs->throttled_reqs)); + busy = bdrv_requests_pending_all(); + busy |= aio_poll(qemu_get_aio_context(), busy); } } @@ -1591,11 +1615,11 @@ void bdrv_delete(BlockDriverState *bs) assert(!bs->job); assert(!bs->in_use); + bdrv_close(bs); + /* remove from list, if necessary */ bdrv_make_anon(bs); - bdrv_close(bs); - g_free(bs); }
If a block driver has no file descriptors to monitor but there are still active requests, it can return 1 from .io_flush(). This is used to spin during synchronous I/O. Stop relying on .io_flush() and instead check QLIST_EMPTY(&bs->tracked_requests) to decide whether there are active requests. This is the first step in removing .io_flush() so that event loops no longer need to have the concept of synchronous I/O. Eventually we may be able to kill synchronous I/O completely by running everything in a coroutine, but that is future work. Note this patch moves bs->throttled_reqs initialization to bdrv_new() so that bdrv_requests_pending(bs) can safely access it. In practice bs is g_malloc0() so the memory is already zeroed but it's safer to initialize the queue properly. In bdrv_delete() make sure to call bdrv_make_anon() *after* bdrv_close() so that the device is still seen by bdrv_drain_all() when iterating bdrv_states. Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com> --- block.c | 50 +++++++++++++++++++++++++++++++++++++------------- 1 file changed, 37 insertions(+), 13 deletions(-)