After the commit 9b536adc ("block: acquire AioContext in bdrv_drain_all()") the aio_poll() function got called for every BlockDriverState, in assumption that every device may have its own AioContext. If we have thousands of disks attached, there are a lot of BlockDriverStates but only a few AioContexts, leading to tons of unnecessary aio_poll() calls.
This patch changes the bdrv_drain_all() function allowing it find shared AioContexts and to call aio_poll() only for unique ones. Cc: Christian Borntraeger <borntrae...@de.ibm.com> Cc: Cornelia Huck <cornelia.h...@de.ibm.com> Cc: Kevin Wolf <kw...@redhat.com> Cc: Paolo Bonzini <pbonz...@redhat.com> Cc: Stefan Hajnoczi <stefa...@redhat.com> Signed-off-by: Alexander Yarygin <yary...@linux.vnet.ibm.com> --- block/io.c | 42 ++++++++++++++++++++++++++---------------- 1 file changed, 26 insertions(+), 16 deletions(-) diff --git a/block/io.c b/block/io.c index e394d92..7502186 100644 --- a/block/io.c +++ b/block/io.c @@ -271,17 +271,6 @@ static bool bdrv_requests_pending(BlockDriverState *bs) return false; } -static bool bdrv_drain_one(BlockDriverState *bs) -{ - bool bs_busy; - - bdrv_flush_io_queue(bs); - bdrv_start_throttled_reqs(bs); - bs_busy = bdrv_requests_pending(bs); - bs_busy |= aio_poll(bdrv_get_aio_context(bs), bs_busy); - return bs_busy; -} - /* * Wait for pending requests to complete on a single BlockDriverState subtree * @@ -294,8 +283,13 @@ static bool bdrv_drain_one(BlockDriverState *bs) */ void bdrv_drain(BlockDriverState *bs) { - while (bdrv_drain_one(bs)) { + bool busy = true; + + while (busy) { /* Keep iterating */ + bdrv_flush_io_queue(bs); + busy = bdrv_requests_pending(bs); + busy |= aio_poll(bdrv_get_aio_context(bs), busy); } } @@ -316,6 +310,7 @@ void bdrv_drain_all(void) /* Always run first iteration so any pending completion BHs run */ bool busy = true; BlockDriverState *bs = NULL; + GSList *aio_ctxs = NULL, *ctx; while ((bs = bdrv_next(bs))) { AioContext *aio_context = bdrv_get_aio_context(bs); @@ -325,17 +320,30 @@ void bdrv_drain_all(void) block_job_pause(bs->job); } aio_context_release(aio_context); + + if (!aio_ctxs || !g_slist_find(aio_ctxs, aio_context)) { + aio_ctxs = g_slist_prepend(aio_ctxs, aio_context); + } } while (busy) { busy = false; - bs = NULL; - while ((bs = bdrv_next(bs))) { - AioContext *aio_context = bdrv_get_aio_context(bs); + for (ctx = aio_ctxs; ctx != NULL; ctx = ctx->next) { + AioContext *aio_context = ctx->data; + bs = NULL; aio_context_acquire(aio_context); - busy |= bdrv_drain_one(bs); + while ((bs = bdrv_next(bs))) { + if (aio_context == bdrv_get_aio_context(bs)) { + bdrv_flush_io_queue(bs); + if (bdrv_requests_pending(bs)) { + busy = true; + aio_poll(aio_context, busy); + } + } + } + busy |= aio_poll(aio_context, false); aio_context_release(aio_context); } } @@ -350,6 +358,7 @@ void bdrv_drain_all(void) } aio_context_release(aio_context); } + g_slist_free(aio_ctxs); } /** @@ -2600,4 +2609,5 @@ void bdrv_flush_io_queue(BlockDriverState *bs) } else if (bs->file) { bdrv_flush_io_queue(bs->file); } + bdrv_start_throttled_reqs(bs); } -- 1.9.1