From: Kevin Wolf <kwolf@redhat.com>
To: Paolo Bonzini <pbonzini@redhat.com>
Cc: qemu-devel@nongnu.org, qemu-block@nongnu.org, eesposit@redhat.com
Subject: Re: [PATCH 10/15] block-backend: always wait for drain before starting operation
Date: Mon, 16 Jan 2023 17:48:59 +0100 [thread overview]
Message-ID: <Y8V/+zAmvRH/CyXA@redhat.com> (raw)
In-Reply-To: <20221212125920.248567-11-pbonzini@redhat.com>
Am 12.12.2022 um 13:59 hat Paolo Bonzini geschrieben:
> All I/O operations call blk_wait_while_drained() immediately after
> blk_inc_in_flight(), except for blk_abort_aio_request() where it
> does not hurt to add such a call. Merge the two functions into one,
> and add a note about a disturbing lack of thread-safety that will
> be fixed shortly.
>
> While at it, make the quiesce_counter check a loop. While the check
> does not have to be "perfect", i.e. it only matters that an endless
> stream of I/Os is stopped sooner or later, it is more logical to check
> the counter repeatedly until it is zero.
>
> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
> ---
> block/block-backend.c | 27 ++++++++-------------------
> 1 file changed, 8 insertions(+), 19 deletions(-)
>
> diff --git a/block/block-backend.c b/block/block-backend.c
> index fe42d53d655d..627d491d4155 100644
> --- a/block/block-backend.c
> +++ b/block/block-backend.c
> @@ -1270,18 +1270,6 @@ static int blk_check_byte_request(BlockBackend *blk, int64_t offset,
> return 0;
> }
>
> -/* To be called between exactly one pair of blk_inc/dec_in_flight() */
> -static void coroutine_fn blk_wait_while_drained(BlockBackend *blk)
> -{
> - assert(blk->in_flight > 0);
> -
> - if (blk->quiesce_counter && !blk->disable_request_queuing) {
> - blk_dec_in_flight(blk);
> - qemu_co_queue_wait(&blk->queued_requests, NULL);
> - blk_inc_in_flight(blk);
> - }
> -}
> -
> /* To be called between exactly one pair of blk_inc/dec_in_flight() */
> static int coroutine_fn
> blk_co_do_preadv_part(BlockBackend *blk, int64_t offset, int64_t bytes,
> @@ -1334,7 +1322,6 @@ int coroutine_fn blk_co_preadv(BlockBackend *blk, int64_t offset,
> IO_OR_GS_CODE();
>
> blk_inc_in_flight(blk);
> - blk_wait_while_drained(blk);
> ret = blk_co_do_preadv_part(blk, offset, bytes, qiov, 0, flags);
> blk_dec_in_flight(blk);
>
> @@ -1349,7 +1336,6 @@ int coroutine_fn blk_co_preadv_part(BlockBackend *blk, int64_t offset,
> IO_OR_GS_CODE();
>
> blk_inc_in_flight(blk);
> - blk_wait_while_drained(blk);
> ret = blk_co_do_preadv_part(blk, offset, bytes, qiov, qiov_offset, flags);
> blk_dec_in_flight(blk);
>
> @@ -1401,7 +1387,6 @@ int coroutine_fn blk_co_pwritev_part(BlockBackend *blk, int64_t offset,
> IO_OR_GS_CODE();
>
> blk_inc_in_flight(blk);
> - blk_wait_while_drained(blk);
> ret = blk_co_do_pwritev_part(blk, offset, bytes, qiov, qiov_offset, flags);
> blk_dec_in_flight(blk);
>
> @@ -1466,6 +1451,14 @@ void blk_inc_in_flight(BlockBackend *blk)
> {
> IO_CODE();
> qatomic_inc(&blk->in_flight);
> + if (!blk->disable_request_queuing) {
> + /* TODO: this is not thread-safe! */
> + while (blk->quiesce_counter) {
> + qatomic_dec(&blk->in_flight);
> + qemu_co_queue_wait(&blk->queued_requests, NULL);
blk_inc_in_flight() must be a coroutine_fn now.
blk_abort_aio_request() and blk_aio_prwv() aren't, but still call it.
> + qatomic_inc(&blk->in_flight);
> + }
> + }
> }
Kevin
next prev parent reply other threads:[~2023-01-16 16:49 UTC|newest]
Thread overview: 22+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-12-12 12:59 [PATCH 00/12] More cleanups and fixes for drain Paolo Bonzini
2022-12-12 12:59 ` [PATCH 01/15] Revert "block: Remove poll parameter from bdrv_parent_drained_begin_single()" Paolo Bonzini
2022-12-12 12:59 ` [PATCH 02/15] Revert "block: Don't poll in bdrv_replace_child_noperm()" Paolo Bonzini
2022-12-12 12:59 ` [PATCH 03/15] block: Pull polling out of bdrv_parent_drained_begin_single() Paolo Bonzini
2022-12-12 12:59 ` [PATCH 04/15] test-bdrv-drain.c: remove test_detach_by_parent_cb() Paolo Bonzini
2022-12-12 12:59 ` [PATCH 05/15] tests/unit/test-bdrv-drain.c: graph setup functions can't run in coroutines Paolo Bonzini
2022-12-12 12:59 ` [PATCH 06/15] tests/qemu-iotests/030: test_stream_parallel should use auto_finalize=False Paolo Bonzini
2022-12-12 12:59 ` [PATCH 07/15] block-backend: enter aio coroutine only after drain Paolo Bonzini
2023-01-16 15:57 ` Kevin Wolf
2022-12-12 12:59 ` [PATCH 08/15] nbd: a BlockExport always has a BlockBackend Paolo Bonzini
2022-12-12 12:59 ` [PATCH 09/15] block-backend: make global properties write-once Paolo Bonzini
2022-12-12 12:59 ` [PATCH 10/15] block-backend: always wait for drain before starting operation Paolo Bonzini
2023-01-16 16:48 ` Kevin Wolf [this message]
2022-12-12 12:59 ` [PATCH 11/15] block-backend: make queued_requests thread-safe Paolo Bonzini
2023-01-11 20:44 ` Stefan Hajnoczi
2023-01-16 16:55 ` Kevin Wolf
2022-12-12 12:59 ` [PATCH 12/15] block: limit bdrv_co_yield_to_drain to drain_begin Paolo Bonzini
2022-12-12 12:59 ` [PATCH 13/15] block: second argument of bdrv_do_drained_end is always NULL Paolo Bonzini
2022-12-12 12:59 ` [PATCH 14/15] block: second argument of bdrv_do_drained_begin and bdrv_drain_poll " Paolo Bonzini
2022-12-12 12:59 ` [PATCH 15/15] block: only get out of coroutine context for polling Paolo Bonzini
2023-01-16 15:51 ` [PATCH 00/12] More cleanups and fixes for drain Kevin Wolf
2023-01-16 17:25 ` Kevin Wolf
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