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. The bdrv_drain_all() function is called in each virtio_reset() call, which in turn is called for every virtio-blk device on initialization, so we got aio_poll() called 'length(device_list)^2' times.
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. For example, startup times with 1000 disks takes over 13 minutes. This patch changes the bdrv_drain_all() function allowing it find shared AioContexts and to call aio_poll() only for unique ones. This results in much better startup times, e.g. 1000 disks do come up within 5 seconds. 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.c | 13 +++++++++++-- 1 file changed, 11 insertions(+), 2 deletions(-) diff --git a/block.c b/block.c index f2f8ae7..7414815 100644 --- a/block.c +++ b/block.c @@ -1994,7 +1994,6 @@ static bool bdrv_drain_one(BlockDriverState *bs) 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; } @@ -2010,8 +2009,12 @@ static bool bdrv_drain_one(BlockDriverState *bs) */ void bdrv_drain(BlockDriverState *bs) { - while (bdrv_drain_one(bs)) { + bool busy = true; + + while (busy) { /* Keep iterating */ + busy = bdrv_drain_one(bs); + busy |= aio_poll(bdrv_get_aio_context(bs), busy); } } @@ -2032,6 +2035,7 @@ void bdrv_drain_all(void) /* Always run first iteration so any pending completion BHs run */ bool busy = true; BlockDriverState *bs; + GList *aio_ctxs = NULL; while (busy) { busy = false; @@ -2041,9 +2045,14 @@ void bdrv_drain_all(void) aio_context_acquire(aio_context); busy |= bdrv_drain_one(bs); + if (!aio_ctxs || !g_list_find(aio_ctxs, aio_context)) { + busy |= aio_poll(aio_context, busy); + aio_ctxs = g_list_append(aio_ctxs, aio_context); + } aio_context_release(aio_context); } } + g_list_free(aio_ctxs); } /* make a BlockDriverState anonymous by removing from bdrv_state and -- 1.9.1