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 0C5B6C678D4 for ; Thu, 2 Mar 2023 15:49:20 +0000 (UTC) Received: from localhost ([::1] helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1pXlAk-0003ld-QS; Thu, 02 Mar 2023 10:48:46 -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 1pXlAi-0003kr-Im for qemu-devel@nongnu.org; Thu, 02 Mar 2023 10:48:44 -0500 Received: from us-smtp-delivery-124.mimecast.com ([170.10.133.124]) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1pXlAg-0003gb-PM for qemu-devel@nongnu.org; Thu, 02 Mar 2023 10:48:44 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1677772121; 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=KjaJIehJSuxVE4TD7Hle85EDXIi8T/+T/Hr+Ow1okHE=; b=VEoJYk6+E4t8h7vx9MhOOB13QvpWzt0UVLu1CLnS3rhkdDBUU776l7a8UvKuZraP5dDXVg ZseJV+UH+yh2ws6Hrv9i7qslnaW2ECvNfKzcx97KtA5zv4dXgc25sHkSPp7+kSrUBI99BY iFYFqgTttuuWjBi9x3hVK6wdNsxYP38= 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-220-n0pOU0zhOrS2bnjkGLWS2w-1; Thu, 02 Mar 2023 10:48:37 -0500 X-MC-Unique: n0pOU0zhOrS2bnjkGLWS2w-1 Received: from smtp.corp.redhat.com (int-mx08.intmail.prod.int.rdu2.redhat.com [10.11.54.8]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id 9D2B1100F90B; Thu, 2 Mar 2023 15:48:36 +0000 (UTC) Received: from localhost (unknown [10.39.193.244]) by smtp.corp.redhat.com (Postfix) with ESMTP id F311DC16027; Thu, 2 Mar 2023 15:48:35 +0000 (UTC) Date: Thu, 2 Mar 2023 10:48:34 -0500 From: Stefan Hajnoczi To: Markus Armbruster Cc: qemu-devel@nongnu.org, Fam Zheng , qemu-block@nongnu.org, Emanuele Giuseppe Esposito , Kevin Wolf , "Dr. David Alan Gilbert" , Hanna Reitz Subject: Re: [PATCH 5/6] hmp: convert handle_hmp_command() to AIO_WAIT_WHILE_UNLOCKED() Message-ID: <20230302154834.GA2497705@fedora> References: <20230301205801.2453491-1-stefanha@redhat.com> <20230301205801.2453491-6-stefanha@redhat.com> <87ttz3sju0.fsf@pond.sub.org> <20230302132205.GB2485531@fedora> <87v8jjjiwx.fsf@pond.sub.org> MIME-Version: 1.0 Content-Type: multipart/signed; micalg=pgp-sha256; protocol="application/pgp-signature"; boundary="dGTtfjuot41NRlXl" Content-Disposition: inline In-Reply-To: <87v8jjjiwx.fsf@pond.sub.org> X-Scanned-By: MIMEDefang 3.1 on 10.11.54.8 Received-SPF: pass client-ip=170.10.133.124; envelope-from=stefanha@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 --dGTtfjuot41NRlXl Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Content-Transfer-Encoding: quoted-printable On Thu, Mar 02, 2023 at 04:02:22PM +0100, Markus Armbruster wrote: > Stefan Hajnoczi writes: >=20 > > On Thu, Mar 02, 2023 at 08:17:43AM +0100, Markus Armbruster wrote: > >> Stefan Hajnoczi writes: > >>=20 > >> > The HMP monitor runs in the main loop thread. Calling > >>=20 > >> Correct. > >>=20 > >> > AIO_WAIT_WHILE(qemu_get_aio_context(), ...) from the main loop threa= d is > >> > equivalent to AIO_WAIT_WHILE_UNLOCKED(NULL, ...) because neither unl= ocks > >> > the AioContext and the latter's assertion that we're in the main loop > >> > succeeds. > >> > > >> > Signed-off-by: Stefan Hajnoczi > >> > --- > >> > monitor/hmp.c | 2 +- > >> > 1 file changed, 1 insertion(+), 1 deletion(-) > >> > > >> > diff --git a/monitor/hmp.c b/monitor/hmp.c > >> > index 2aa85d3982..5ecbdac802 100644 > >> > --- a/monitor/hmp.c > >> > +++ b/monitor/hmp.c > >> > @@ -1167,7 +1167,7 @@ void handle_hmp_command(MonitorHMP *mon, const= char *cmdline) > >> > Coroutine *co =3D qemu_coroutine_create(handle_hmp_command_= co, &data); > >> > monitor_set_cur(co, &mon->common); > >> > aio_co_enter(qemu_get_aio_context(), co); > >> > - AIO_WAIT_WHILE(qemu_get_aio_context(), !data.done); > >> > + AIO_WAIT_WHILE_UNLOCKED(NULL, !data.done); > >> > } > >> > =20 > >> > qobject_unref(qdict); > >>=20 > >> Acked-by: Markus Armbruster > >>=20 > >> For an R-by, I need to understand this in more detail. I'm not famili= ar > >> with the innards of AIO_WAIT_WHILE() & friends, so I need to go real > >> slow. > >>=20 > >> We change > >>=20 > >> ctx from qemu_get_aio_context() to NULL > >> unlock from true to false > >>=20 > >> in > >>=20 > >> bool waited_ =3D false; \ > >> AioWait *wait_ =3D &global_aio_wait; \ > >> AioContext *ctx_ =3D (ctx); \ > >> /* Increment wait_->num_waiters before evaluating cond. */ \ > >> qatomic_inc(&wait_->num_waiters); \ > >> /* Paired with smp_mb in aio_wait_kick(). */ \ > >> smp_mb(); \ > >> if (ctx_ && in_aio_context_home_thread(ctx_)) { \ > >> while ((cond)) { \ > >> aio_poll(ctx_, true); \ > >> waited_ =3D true; \ > >> } \ > >> } else { \ > >> assert(qemu_get_current_aio_context() =3D=3D = \ > >> qemu_get_aio_context()); \ > >> while ((cond)) { \ > >> if (unlock && ctx_) { \ > >> aio_context_release(ctx_); \ > >> } \ > >> aio_poll(qemu_get_aio_context(), true); \ > >> if (unlock && ctx_) { \ > >> aio_context_acquire(ctx_); \ > >> } \ > >> waited_ =3D true; \ > >> } \ > >> } \ > >> qatomic_dec(&wait_->num_waiters); \ > >> waited_; }) > >>=20 > >> qemu_get_aio_context() is non-null here, correct? > > > > qemu_get_aio_context() always returns the main loop thread's AioContext. >=20 > So it's non-null. Yes. Sorry, I should have answered directly :). > > qemu_get_current_aio_context() returns the AioContext that was most > > recently set in the my_aiocontext thread-local variable for IOThreads, > > the main loop's AioContext for BQL threads, or NULL for threads > > that don't use AioContext at all. > > > >> What's the value of in_aio_context_home_thread(qemu_get_aio_context())? > > > > This function checks whether the given AioContext is associated with > > this thread. In a BQL thread it returns true if the context is the main > > loop's AioContext. In an IOThread it returns true if the context is the > > IOThread's AioContext. Otherwise it returns false. >=20 > I guess that means in_aio_context_home_thread(qemu_get_aio_context()) is > true in the main thread. >=20 > Before the patch, the if's condition is true, and we execute >=20 > while ((cond)) { \ > aio_poll(ctx_, true); \ > waited_ =3D true; \ > } \ >=20 > Afterwards, it's false, and we execute >=20 > >> } \ > >> qatomic_dec(&wait_->num_waiters); \ > >> waited_; }) > >>=20 > >> qemu_get_aio_context() is non-null here, correct? > > > > qemu_get_aio_context() always returns the main loop thread's AioContext. >=20 > So it's non-null. >=20 > > qemu_get_current_aio_context() returns the AioContext that was most > > recently set in the my_aiocontext thread-local variable for IOThreads, > > the main loop's AioContext for BQL threads, or NULL for threads > > that don't use AioContext at all. > > > >> What's the value of in_aio_context_home_thread(qemu_get_aio_context())? > > > > This function checks whether the given AioContext is associated with > > this thread. In a BQL thread it returns true if the context is the main > > loop's AioContext. In an IOThread it returns true if the context is the > > IOThread's AioContext. Otherwise it returns false. >=20 > I guess that means in_aio_context_home_thread(qemu_get_aio_context()) is > true in the main thread. Yes. > Before the patch, the if's condition is true, and we execute >=20 > while ((cond)) { \ > aio_poll(ctx_, true); \ > waited_ =3D true; \ > } \ >=20 > Afterwards, it's false, and we instead execute >=20 > assert(qemu_get_current_aio_context() =3D=3D = \ > qemu_get_aio_context()); \ > while ((cond)) { \ > if (unlock && ctx_) { \ > aio_context_release(ctx_); \ > } \ > aio_poll(qemu_get_aio_context(), true); \ > if (unlock && ctx_) { \ > aio_context_acquire(ctx_); \ > } \ > waited_ =3D true; \ > } \ >=20 > The assertion is true: both operands of =3D=3D are the main loop's > AioContext. Yes. > The if conditions are false, because unlock is. >=20 > Therefore, we execute the exact same code. >=20 > All correct? Yes, exactly. Stefan --dGTtfjuot41NRlXl Content-Type: application/pgp-signature; name="signature.asc" -----BEGIN PGP SIGNATURE----- iQEzBAEBCAAdFiEEhpWov9P5fNqsNXdanKSrs4Grc8gFAmQAxVIACgkQnKSrs4Gr c8iA1Qf+KwvbHkcnFGI64YTzP4ix/G6WAsB5jaMtVE333Dn8Amd/8jZ5Roq4Eed0 O/gnm9c/hnf/o6ninCBHkePFfwF4wFhdnwbhq0PgeQHO9yKZRZXyYzZoRj++BkN/ Ot3VfcakLNqBuRmxFjc8KifbDekZElaaNRlxM9ySLSKZpdbj6gspX4EPKyikpXsd WaX0e7appYE/G03V9Hh+3xQ2v4DEjpuAmUWBxecCbYUUoJR6JUNdg9tuuiyOTf1F gspl2KeyvkH0hlA4gjaClGGnH1nXeihj3N+Ay962z52D6xQ60ezXKUtWu5qiO67d oFBtzYGQKQQDyuRG5l9j6HqKx/cu+g== =/pHA -----END PGP SIGNATURE----- --dGTtfjuot41NRlXl--