From patchwork Thu Aug 6 13:18:01 2020 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Stefan Hajnoczi X-Patchwork-Id: 277022 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-8.1 required=3.0 tests=BAYES_00,DKIM_INVALID, DKIM_SIGNED, HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH, MAILING_LIST_MULTI, MIME_BASE64_TEXT,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 044C0C433E0 for ; Thu, 6 Aug 2020 13:19:28 +0000 (UTC) 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 mail.kernel.org (Postfix) with ESMTPS id E65992313B for ; Thu, 6 Aug 2020 13:19:27 +0000 (UTC) Authentication-Results: mail.kernel.org; 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Thu, 6 Aug 2020 13:18:17 +0000 (UTC) Received: from localhost (ovpn-114-7.ams2.redhat.com [10.36.114.7]) by smtp.corp.redhat.com (Postfix) with ESMTP id AD8605F1EF; Thu, 6 Aug 2020 13:18:13 +0000 (UTC) From: Stefan Hajnoczi To: qemu-devel@nongnu.org Subject: [PATCH v3 2/3] async: always set ctx->notified in aio_notify() Date: Thu, 6 Aug 2020 14:18:01 +0100 Message-Id: <20200806131802.569478-3-stefanha@redhat.com> In-Reply-To: <20200806131802.569478-1-stefanha@redhat.com> References: <20200806131802.569478-1-stefanha@redhat.com> MIME-Version: 1.0 X-Scanned-By: MIMEDefang 2.79 on 10.5.11.15 Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=stefanha@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Received-SPF: pass client-ip=205.139.110.120; envelope-from=stefanha@redhat.com; helo=us-smtp-1.mimecast.com X-detected-operating-system: by eggs.gnu.org: First seen = 2020/08/06 00:24:10 X-ACL-Warn: Detected OS = Linux 2.2.x-3.x [generic] [fuzzy] X-Spam_score_int: -13 X-Spam_score: -1.4 X-Spam_bar: - X-Spam_report: (-1.4 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-1, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, MIME_BASE64_TEXT=1.741, RCVD_IN_DNSWL_NONE=-0.0001, RCVD_IN_MSPIKE_H3=-0.01, RCVD_IN_MSPIKE_WL=-0.01, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Fam Zheng , Paolo Bonzini , qemu-block@nongnu.org, Stefan Hajnoczi Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" aio_notify() does not set ctx->notified when called with ctx->aio_notify_me disabled. Therefore aio_notify_me needs to be enabled during polling. This is suboptimal since expensive event_notifier_set(&ctx->notifier) and event_notifier_test_and_clear(&ctx->notifier) calls are required when ctx->aio_notify_me is enabled. Change aio_notify() so that aio->notified is always set, regardless of ctx->aio_notify_me. This will make polling cheaper since ctx->aio_notify_me can remain disabled. Move the event_notifier_test_and_clear() to the fd handler function (which is now no longer an empty function so "dummy" has been dropped from its name). The next patch takes advantage of this by optimizing polling in util/aio-posix.c. Signed-off-by: Stefan Hajnoczi Reviewed-by: Paolo Bonzini --- util/async.c | 32 +++++++++++++++++++++----------- 1 file changed, 21 insertions(+), 11 deletions(-) diff --git a/util/async.c b/util/async.c index d9f987e133..99e15644d9 100644 --- a/util/async.c +++ b/util/async.c @@ -419,25 +419,32 @@ LuringState *aio_get_linux_io_uring(AioContext *ctx) void aio_notify(AioContext *ctx) { - /* Write e.g. bh->scheduled before reading ctx->notify_me. Pairs + /* + * Write e.g. bh->flags before writing ctx->notified. Pairs with smp_mb in + * aio_notify_accept. + */ + smp_wmb(); + atomic_set(&ctx->notified, true); + + /* + * Write ctx->notified before reading ctx->notify_me. Pairs * with smp_mb in aio_ctx_prepare or aio_poll. */ smp_mb(); if (atomic_read(&ctx->notify_me)) { event_notifier_set(&ctx->notifier); - atomic_mb_set(&ctx->notified, true); } } void aio_notify_accept(AioContext *ctx) { - if (atomic_xchg(&ctx->notified, false) -#ifdef WIN32 - || true -#endif - ) { - event_notifier_test_and_clear(&ctx->notifier); - } + atomic_set(&ctx->notified, false); + + /* + * Write ctx->notified before reading e.g. bh->flags. Pairs with smp_mb in + * aio_notify. + */ + smp_wmb(); } static void aio_timerlist_notify(void *opaque, QEMUClockType type) @@ -445,8 +452,11 @@ static void aio_timerlist_notify(void *opaque, QEMUClockType type) aio_notify(opaque); } -static void aio_context_notifier_dummy_cb(EventNotifier *e) +static void aio_context_notifier_cb(EventNotifier *e) { + AioContext *ctx = container_of(e, AioContext, notifier); + + event_notifier_test_and_clear(&ctx->notifier); } /* Returns true if aio_notify() was called (e.g. a BH was scheduled) */ @@ -508,7 +518,7 @@ AioContext *aio_context_new(Error **errp) aio_set_event_notifier(ctx, &ctx->notifier, false, - aio_context_notifier_dummy_cb, + aio_context_notifier_cb, aio_context_notifier_poll); #ifdef CONFIG_LINUX_AIO ctx->linux_aio = NULL;