From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from lists.gnu.org (lists.gnu.org [209.51.188.17]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 536CEC4332F for ; Wed, 9 Nov 2022 12:29:43 +0000 (UTC) Received: from localhost ([::1] helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1oskCQ-00056i-Hu; Wed, 09 Nov 2022 07:28:58 -0500 Received: from eggs.gnu.org ([2001:470:142:3::10]) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1oskCL-00053w-Qj for qemu-devel@nongnu.org; Wed, 09 Nov 2022 07:28:54 -0500 Received: from us-smtp-delivery-124.mimecast.com ([170.10.129.124]) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1oskCK-0007bO-1i for qemu-devel@nongnu.org; Wed, 09 Nov 2022 07:28:53 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1667996931; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=qCuUJa0VPDsqXDx+XzFGqn8Jfj9u/LtQeK0wKkgKolk=; b=TQyGY5uViMVeeT1K58ACsoEOIIhtKno+3CvxgfQiebxWiE3yNfxZY0KNVB4SmSvu8nGoaU 21nA+U+V0jm8gEuZTg1DtHK5p+Rlffa6M08gZwpS609nGrK+qerejdLrgPAXRxPnfCZG11 9JYKIfVx6zUNw67sqlXXmMM7rgvD41A= Received: from mimecast-mx02.redhat.com (mimecast-mx02.redhat.com [66.187.233.88]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id us-mta-99-8lgE_64VOPWHsWK7GAKWNg-1; Wed, 09 Nov 2022 07:28:47 -0500 X-MC-Unique: 8lgE_64VOPWHsWK7GAKWNg-1 Received: from smtp.corp.redhat.com (int-mx10.intmail.prod.int.rdu2.redhat.com [10.11.54.10]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id 526CE858F13; Wed, 9 Nov 2022 12:28:47 +0000 (UTC) Received: from redhat.com (unknown [10.39.193.183]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 2D44F492B17; Wed, 9 Nov 2022 12:28:46 +0000 (UTC) Date: Wed, 9 Nov 2022 13:28:44 +0100 From: Kevin Wolf To: Vladimir Sementsov-Ogievskiy Cc: qemu-block@nongnu.org, eesposit@redhat.com, stefanha@redhat.com, hreitz@redhat.com, pbonzini@redhat.com, qemu-devel@nongnu.org Subject: Re: [PATCH 02/13] test-bdrv-drain: Don't yield in .bdrv_co_drained_begin/end() Message-ID: References: <20221108123738.530873-1-kwolf@redhat.com> <20221108123738.530873-3-kwolf@redhat.com> <7c2df33b-c7a2-6ed6-d198-1e70c1a009d5@yandex-team.ru> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <7c2df33b-c7a2-6ed6-d198-1e70c1a009d5@yandex-team.ru> X-Scanned-By: MIMEDefang 3.1 on 10.11.54.10 Received-SPF: pass client-ip=170.10.129.124; envelope-from=kwolf@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -20 X-Spam_score: -2.1 X-Spam_bar: -- X-Spam_report: (-2.1 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.001, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_NONE=-0.0001, RCVD_IN_MSPIKE_H2=-0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=unavailable autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Am 09.11.2022 um 11:50 hat Vladimir Sementsov-Ogievskiy geschrieben: > On 11/8/22 15:37, Kevin Wolf wrote: > > We want to change .bdrv_co_drained_begin/end() back to be non-coroutine > > callbacks, so in preparation, avoid yielding in their implementation. > > > > This does almost the same as the existing logic in bdrv_drain_invoke(), > > by creating and entering coroutines internally. However, since the test > > case is by far the heaviest user of coroutine code in drain callbacks, > > it is preferable to have the complexity in the test case rather than the > > drain core, which is already complicated enough without this. > > > > The behaviour for bdrv_drain_begin() is unchanged because we increase > > bs->in_flight and this is still polled. However, bdrv_drain_end() > > doesn't wait for the spawned coroutine to complete any more. This is > > fine, we don't rely on bdrv_drain_end() restarting all operations > > immediately before the next aio_poll(). > > > > Signed-off-by: Kevin Wolf > > --- > > tests/unit/test-bdrv-drain.c | 64 ++++++++++++++++++++++++++---------- > > 1 file changed, 46 insertions(+), 18 deletions(-) > > > > diff --git a/tests/unit/test-bdrv-drain.c b/tests/unit/test-bdrv-drain.c > > index 09dc4a4891..24f34e24ad 100644 > > --- a/tests/unit/test-bdrv-drain.c > > +++ b/tests/unit/test-bdrv-drain.c > > @@ -38,12 +38,22 @@ typedef struct BDRVTestState { > > bool sleep_in_drain_begin; > > } BDRVTestState; > > +static void coroutine_fn sleep_in_drain_begin(void *opaque) > > +{ > > + BlockDriverState *bs = opaque; > > + > > + qemu_co_sleep_ns(QEMU_CLOCK_REALTIME, 100000); > > + bdrv_dec_in_flight(bs); > > +} > > + > > static void coroutine_fn bdrv_test_co_drain_begin(BlockDriverState *bs) > > { > > BDRVTestState *s = bs->opaque; > > s->drain_count++; > > if (s->sleep_in_drain_begin) { > > - qemu_co_sleep_ns(QEMU_CLOCK_REALTIME, 100000); > > + Coroutine *co = qemu_coroutine_create(sleep_in_drain_begin, bs); > > + bdrv_inc_in_flight(bs); > > + aio_co_enter(bdrv_get_aio_context(bs), co); > > } > > } > > @@ -1916,6 +1926,21 @@ static int coroutine_fn bdrv_replace_test_co_preadv(BlockDriverState *bs, > > return 0; > > } > > +static void coroutine_fn bdrv_replace_test_drain_co(void *opaque) > > +{ > > + BlockDriverState *bs = opaque; > > + BDRVReplaceTestState *s = bs->opaque; > > + > > + /* Keep waking io_co up until it is done */ > > + while (s->io_co) { > > + aio_co_wake(s->io_co); > > + s->io_co = NULL; > > + qemu_coroutine_yield(); > > + } > > + s->drain_co = NULL; > > + bdrv_dec_in_flight(bs); > > +} > > Same question, don't we need aio_wait_kick() after decrement in_flight. > > Also, seems we have here extra waiting level: a special coroutine that waits in a loop. > > Could we just do in .drain_begin: > > if (s->io_co) { > bdrv_inc_in_flight(bs); > } > > and in .co_preadv instead of waking s->drain_co simply > > if (s->drain_count == 1) { > bdrv_dec_in_flight(bs); > aio_wait_kick(); > } > > or even better, do inc in_flight when io_co becomes not NULL. I just did the minimal transformation of the existing code in the test case. These test cases often test specific interactions between coroutines, so I could imagine that the additional yield is not just some inefficient code, but coroutines that yield multiple times could actually be the scenario that is supposed to be tested. I didn't check it for this one, but making test cases more efficient isn't automatically a good thing if they then end up not testing certain code paths any more. So if you intend to make a change here, it would need a careful analysis of all test cases that use the driver. Kevin