From patchwork Wed Aug 5 10:00:51 2020 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Patchwork-Submitter: Stefan Hajnoczi X-Patchwork-Id: 11701695 Return-Path: Received: from mail.kernel.org (pdx-korg-mail-1.web.codeaurora.org [172.30.200.123]) by pdx-korg-patchwork-2.web.codeaurora.org (Postfix) with ESMTP id A6B351731 for ; Wed, 5 Aug 2020 10:05:29 +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 7B9782173E for ; Wed, 5 Aug 2020 10:05:29 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="VS3YIPjs" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 7B9782173E Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=redhat.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=qemu-devel-bounces+patchwork-qemu-devel=patchwork.kernel.org@nongnu.org Received: from localhost ([::1]:55102 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1k3GIa-00040c-P2 for patchwork-qemu-devel@patchwork.kernel.org; Wed, 05 Aug 2020 06:05:28 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:37614) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1k3GEW-0005pg-Tn for qemu-devel@nongnu.org; Wed, 05 Aug 2020 06:01:17 -0400 Received: from us-smtp-1.mimecast.com ([205.139.110.61]:29494 helo=us-smtp-delivery-1.mimecast.com) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_CBC_SHA1:256) (Exim 4.90_1) (envelope-from ) id 1k3GEU-0000UW-Gn for qemu-devel@nongnu.org; Wed, 05 Aug 2020 06:01:16 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1596621673; 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: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=LvLhYWwqvdmgtM6yZ1tfDDwvqZo2lbAzSYkQQNfkwsc=; b=VS3YIPjs3/N0osT797Qlgep/iQQtEZfnnFIFRKj+yBn/1+MbrngRkBKLvL1jyBe+eudTMM Ptsn/bredfOvTW3jjUcAU9yL6B7gXM7Ll9UCssi2RN04Se2LdvAlNpr3IrgFbc1Brv2oNL 3Z3jcqRVTmwlFzbM7mH3uDeob7OwgZk= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-392-tE24ClGKOhaVISEZ8Oo1CQ-1; Wed, 05 Aug 2020 06:01:11 -0400 X-MC-Unique: tE24ClGKOhaVISEZ8Oo1CQ-1 Received: from smtp.corp.redhat.com (int-mx01.intmail.prod.int.phx2.redhat.com [10.5.11.11]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id A20F0101C8B1; Wed, 5 Aug 2020 10:01:10 +0000 (UTC) Received: from localhost (ovpn-114-155.ams2.redhat.com [10.36.114.155]) by smtp.corp.redhat.com (Postfix) with ESMTP id 17B1689512; Wed, 5 Aug 2020 10:01:04 +0000 (UTC) From: Stefan Hajnoczi To: qemu-devel@nongnu.org Subject: [PATCH v2 3/3] aio-posix: keep aio_notify_me disabled during polling Date: Wed, 5 Aug 2020 11:00:51 +0100 Message-Id: <20200805100051.361547-4-stefanha@redhat.com> In-Reply-To: <20200805100051.361547-1-stefanha@redhat.com> References: <20200805100051.361547-1-stefanha@redhat.com> MIME-Version: 1.0 X-Scanned-By: MIMEDefang 2.79 on 10.5.11.11 X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Received-SPF: pass client-ip=205.139.110.61; envelope-from=stefanha@redhat.com; helo=us-smtp-delivery-1.mimecast.com X-detected-operating-system: by eggs.gnu.org: First seen = 2020/08/05 04:10:11 X-ACL-Warn: Detected OS = Linux 2.2.x-3.x [generic] [fuzzy] X-Spam_score_int: -40 X-Spam_score: -4.1 X-Spam_bar: ---- X-Spam_report: (-4.1 / 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, RCVD_IN_DNSWL_NONE=-0.0001, RCVD_IN_MSPIKE_H2=-1, 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+patchwork-qemu-devel=patchwork.kernel.org@nongnu.org Sender: "Qemu-devel" Polling only monitors the ctx->notified field and does not need the ctx->notifier EventNotifier to be signalled. Keep ctx->aio_notify_me disabled while polling to avoid unnecessary EventNotifier syscalls. This optimization improves virtio-blk 4KB random read performance by 18%. The following results are with an IOThread and the null-co block driver: Test IOPS Error Before 244518.62 ± 1.20% After 290706.11 ± 0.44% Signed-off-by: Stefan Hajnoczi --- util/aio-posix.c | 59 +++++++++++++++++++++++++----------------------- 1 file changed, 31 insertions(+), 28 deletions(-) diff --git a/util/aio-posix.c b/util/aio-posix.c index 1b2a3af65b..8d10910bcf 100644 --- a/util/aio-posix.c +++ b/util/aio-posix.c @@ -464,9 +464,6 @@ static bool remove_idle_poll_handlers(AioContext *ctx, int64_t now) * * Polls for a given time. * - * Note that ctx->notify_me must be non-zero so this function can detect - * aio_notify(). - * * Note that the caller must have incremented ctx->list_lock. * * Returns: true if progress was made, false otherwise @@ -476,7 +473,6 @@ static bool run_poll_handlers(AioContext *ctx, int64_t max_ns, int64_t *timeout) bool progress; int64_t start_time, elapsed_time; - assert(ctx->notify_me); assert(qemu_lockcnt_count(&ctx->list_lock) > 0); trace_run_poll_handlers_begin(ctx, max_ns, *timeout); @@ -520,8 +516,6 @@ static bool run_poll_handlers(AioContext *ctx, int64_t max_ns, int64_t *timeout) * @timeout: timeout for blocking wait, computed by the caller and updated if * polling succeeds. * - * ctx->notify_me must be non-zero so this function can detect aio_notify(). - * * Note that the caller must have incremented ctx->list_lock. * * Returns: true if progress was made, false otherwise @@ -566,23 +560,6 @@ bool aio_poll(AioContext *ctx, bool blocking) */ assert(in_aio_context_home_thread(ctx)); - /* aio_notify can avoid the expensive event_notifier_set if - * everything (file descriptors, bottom halves, timers) will - * be re-evaluated before the next blocking poll(). This is - * already true when aio_poll is called with blocking == false; - * if blocking == true, it is only true after poll() returns, - * so disable the optimization now. - */ - if (blocking) { - atomic_set(&ctx->notify_me, atomic_read(&ctx->notify_me) + 2); - /* - * Write ctx->notify_me before computing the timeout - * (reading bottom half flags, etc.). Pairs with - * smp_mb in aio_notify(). - */ - smp_mb(); - } - qemu_lockcnt_inc(&ctx->list_lock); if (ctx->poll_max_ns) { @@ -597,15 +574,41 @@ bool aio_poll(AioContext *ctx, bool blocking) * system call---a single round of run_poll_handlers_once suffices. */ if (timeout || ctx->fdmon_ops->need_wait(ctx)) { + bool use_notify_me = timeout != 0; + + /* + * aio_notify can avoid the expensive event_notifier_set if + * everything (file descriptors, bottom halves, timers) will + * be re-evaluated before the next blocking poll(). This is + * already true when aio_poll is called with blocking == false; + * if blocking == true, it is only true after poll() returns, + * so disable the optimization now. + */ + if (use_notify_me) { + atomic_set(&ctx->notify_me, atomic_read(&ctx->notify_me) + 2); + /* + * Write ctx->notify_me before reading ctx->notified. Pairs with + * smp_mb in aio_notify(). + */ + smp_mb(); + + /* Don't block if aio_notify() was called */ + if (atomic_read(&ctx->notified)) { + timeout = 0; + } + } + ret = ctx->fdmon_ops->wait(ctx, &ready_list, timeout); - } - if (blocking) { - /* Finish the poll before clearing the flag. */ - atomic_store_release(&ctx->notify_me, atomic_read(&ctx->notify_me) - 2); - aio_notify_accept(ctx); + if (use_notify_me) { + /* Finish the poll before clearing the flag. */ + atomic_store_release(&ctx->notify_me, + atomic_read(&ctx->notify_me) - 2); + } } + aio_notify_accept(ctx); + /* Adjust polling time */ if (ctx->poll_max_ns) { int64_t block_ns = qemu_clock_get_ns(QEMU_CLOCK_REALTIME) - start;