From cfe29d8294e06420e15d4938421ae006c8ac49e7 Mon Sep 17 00:00:00 2001 From: Kevin Wolf Date: Tue, 18 Sep 2018 17:09:16 +0200 Subject: block: Use a single global AioWait When draining a block node, we recurse to its parent and for subtree drains also to its children. A single AIO_WAIT_WHILE() is then used to wait for bdrv_drain_poll() to become true, which depends on all of the nodes we recursed to. However, if the respective child or parent becomes quiescent and calls bdrv_wakeup(), only the AioWait of the child/parent is checked, while AIO_WAIT_WHILE() depends on the AioWait of the original node. Fix this by using a single AioWait for all callers of AIO_WAIT_WHILE(). This may mean that the draining thread gets a few more unnecessary wakeups because an unrelated operation got completed, but we already wake it up when something _could_ have changed rather than only if it has certainly changed. Apart from that, drain is a slow path anyway. In theory it would be possible to use wakeups more selectively and still correctly, but the gains are likely not worth the additional complexity. In fact, this patch is a nice simplification for some places in the code. Signed-off-by: Kevin Wolf Reviewed-by: Eric Blake Reviewed-by: Max Reitz --- block.c | 5 ----- 1 file changed, 5 deletions(-) (limited to 'block.c') diff --git a/block.c b/block.c index a381c8ece8..c298ca6a19 100644 --- a/block.c +++ b/block.c @@ -4886,11 +4886,6 @@ AioContext *bdrv_get_aio_context(BlockDriverState *bs) return bs ? bs->aio_context : qemu_get_aio_context(); } -AioWait *bdrv_get_aio_wait(BlockDriverState *bs) -{ - return bs ? &bs->wait : NULL; -} - void bdrv_coroutine_enter(BlockDriverState *bs, Coroutine *co) { aio_co_enter(bdrv_get_aio_context(bs), co); -- cgit v1.2.3