On 13/05/2015 17:18, Alexander Yarygin wrote:
> 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 should actually call bdrv_drain(). Can you fix that?
> 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.
I'm not sure this patch is correct. You may have to call aio_poll
multiple times before a BlockDriverState is drained.
Paolo
> 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
>
