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 X-Spam-Level: X-Spam-Status: No, score=-12.7 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI, SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_AGENT_GIT autolearn=unavailable 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 6A23EC4363C for ; Thu, 8 Oct 2020 15:28:12 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 0DA832184D for ; Thu, 8 Oct 2020 15:28:12 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=kernel-dk.20150623.gappssmtp.com header.i=@kernel-dk.20150623.gappssmtp.com header.b="TDVK74UH" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1730996AbgJHP2I (ORCPT ); Thu, 8 Oct 2020 11:28:08 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:37456 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1731010AbgJHP2C (ORCPT ); Thu, 8 Oct 2020 11:28:02 -0400 Received: from mail-io1-xd42.google.com (mail-io1-xd42.google.com [IPv6:2607:f8b0:4864:20::d42]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id D72CAC0613D6 for ; Thu, 8 Oct 2020 08:28:00 -0700 (PDT) Received: by mail-io1-xd42.google.com with SMTP id y20so2411491iod.5 for ; Thu, 08 Oct 2020 08:28:00 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel-dk.20150623.gappssmtp.com; s=20150623; h=from:to:cc:subject:date:message-id:in-reply-to:references :mime-version:content-transfer-encoding; bh=m8iZ8MjkSc6erbT/UXuLX8pK+PMOfNjl6qhqMPOTqMQ=; b=TDVK74UH5Cx1P4TZPLEfge0uEYCsREV3Ep420h4PYroi4S1NxPWSCc2wbh1SY9LSZS IYBZ3286+WCNciOgwdhueW3w+kS9HCqeVSGrIVXChmhhZlInS1bSMCzfLJjL0dGj3cBz S7IeRN9S5w2rQMpK9q1KdpSful71GMMb0o4j/rFkBuL7GveYD4ocLy3UqvKgqBiGD27d U0MeRhqcDmLYznPEU1hpmTDfiXDCah0+ZnPViog8jF1C6si9fJXK9d4yFHlIJcUHsL+A RXlztD/bWiI4z+Gr2kd5v2uuXD7SdRxuDxzgNobOlpZIFhzsPH1Xf7oShdBTcJJoN91n ZFcg== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:from:to:cc:subject:date:message-id:in-reply-to :references:mime-version:content-transfer-encoding; bh=m8iZ8MjkSc6erbT/UXuLX8pK+PMOfNjl6qhqMPOTqMQ=; b=sBpZfVucF67o4kBSnQrLDBvETOx14b1yZr5LYWhDw1Y6OInttNeNGNVNM7YepAjtQy VDWDfI8JOjbiqCZX2l4zeBDn8IZ+OUctGASKa7d8MySMz2dDJSRb6MRdAlTzMeDRJrtA UDLAg6FkZ9YnqUUwD88EamkmOhMaZhgXvTpjK1xbz67x2MTURtzaDeffU7TYdzyEy2SF 81Kjjv+1SzbXjwwIPVlXtOGr2nRCQneYYLPwCfER8VozkLdcGydMK88GcqjtCzyQAf5b il+4Ao4ywhmqP3p+HVVwcwzyF2vSPPSFmI4fFHvuc2buk7PGRvlBd04JEq9VOpMK9vmg NIJQ== X-Gm-Message-State: AOAM5323Q6JfHA8grQGEQTTtdTXIBqiMLSdn8L0+HFq7FStip5lDVCtX aDPbQjAiexupxm1n012cDVTOCw== X-Google-Smtp-Source: ABdhPJwVRB/C7li7I0p6fC6QrodonEwUPbNeUGqrvSEOZ4X7lkqXM8jleZiOqjeOZsb9uIZW7PQXfQ== X-Received: by 2002:a02:3213:: with SMTP id j19mr7167710jaa.135.1602170880139; Thu, 08 Oct 2020 08:28:00 -0700 (PDT) Received: from p1.localdomain ([65.144.74.34]) by smtp.gmail.com with ESMTPSA id l77sm2866260ill.4.2020.10.08.08.27.59 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 08 Oct 2020 08:27:59 -0700 (PDT) From: Jens Axboe To: linux-kernel@vger.kernel.org, io-uring@vger.kernel.org Cc: peterz@infradead.org, oleg@redhat.com, tglx@linutronix.de, Jens Axboe , Roman Gershman Subject: [PATCH 4/4] task_work: use TIF_NOTIFY_SIGNAL if available Date: Thu, 8 Oct 2020 09:27:52 -0600 Message-Id: <20201008152752.218889-5-axboe@kernel.dk> X-Mailer: git-send-email 2.28.0 In-Reply-To: <20201008152752.218889-1-axboe@kernel.dk> References: <20201008152752.218889-1-axboe@kernel.dk> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: io-uring@vger.kernel.org If the arch supports TIF_NOTIFY_SIGNAL, then use that for TWA_SIGNAL as it's more efficient than using the signal delivery method. This is especially true on threaded applications, where ->sighand is shared across threads, but it's also lighter weight on non-shared cases. io_uring is a heavy consumer of TWA_SIGNAL based task_work. On my test box, even just using 16 threads shows a nice improvement running an io_uring based echo server. stock kernel: 0.01% <= 0.1 milliseconds 95.86% <= 0.2 milliseconds 98.27% <= 0.3 milliseconds 99.71% <= 0.4 milliseconds 100.00% <= 0.5 milliseconds 100.00% <= 0.6 milliseconds 100.00% <= 0.7 milliseconds 100.00% <= 0.8 milliseconds 100.00% <= 0.9 milliseconds 100.00% <= 1.0 milliseconds 100.00% <= 1.1 milliseconds 100.00% <= 2 milliseconds 100.00% <= 3 milliseconds 100.00% <= 3 milliseconds 1378930.00 requests per second ~1600% CPU 1.38M requests/second, and all 16 CPUs are maxed out. patched kernel: 0.01% <= 0.1 milliseconds 98.24% <= 0.2 milliseconds 99.47% <= 0.3 milliseconds 99.99% <= 0.4 milliseconds 100.00% <= 0.5 milliseconds 100.00% <= 0.6 milliseconds 100.00% <= 0.7 milliseconds 100.00% <= 0.8 milliseconds 100.00% <= 0.9 milliseconds 100.00% <= 1.2 milliseconds 1666111.38 requests per second ~1450% CPU 1.67M requests/second, and we're no longer just hammering on the sighand lock. The original reporter states: "For 5.7.15 my benchmark achieves 1.6M qps and system cpu is at ~80%. for 5.7.16 or later it achieves only 1M qps and the system cpu is is at ~100%" with the only difference there being that TWA_SIGNAL is used unconditionally in 5.7.16, since we need it to be able to solve an inability to run task_work if the application is waiting in the kernel already on an event that needs task_work run to be satisfied. Also see commit 0ba9c9edcd15. Reported-by: Roman Gershman Signed-off-by: Jens Axboe --- kernel/task_work.c | 41 +++++++++++++++++++++++++++++------------ 1 file changed, 29 insertions(+), 12 deletions(-) diff --git a/kernel/task_work.c b/kernel/task_work.c index 613b2d634af8..95604e57af46 100644 --- a/kernel/task_work.c +++ b/kernel/task_work.c @@ -5,6 +5,34 @@ static struct callback_head work_exited; /* all we need is ->next == NULL */ +/* + * TWA_SIGNAL signaling - use TIF_NOTIFY_SIGNAL, if available, as it's faster + * than TIF_SIGPENDING as there's no dependency on ->sighand. The latter is + * shared for threads, and can cause contention on sighand->lock. Even for + * the non-threaded case TIF_NOTIFY_SIGNAL is more efficient, as no locking + * or IRQ disabling is involved for notification (or running) purposes. + */ +static void task_work_notify_signal(struct task_struct *task) +{ +#ifdef TIF_NOTIFY_SIGNAL + set_notify_signal(task); +#else + unsigned long flags; + + /* + * Only grab the sighand lock if we don't already have some + * task_work pending. This pairs with the smp_store_mb() + * in get_signal(), see comment there. + */ + if (!(READ_ONCE(task->jobctl) & JOBCTL_TASK_WORK) && + lock_task_sighand(task, &flags)) { + task->jobctl |= JOBCTL_TASK_WORK; + signal_wake_up(task, 0); + unlock_task_sighand(task, &flags); + } +#endif +} + /** * task_work_add - ask the @task to execute @work->func() * @task: the task which should run the callback @@ -28,7 +56,6 @@ int task_work_add(struct task_struct *task, struct callback_head *work, int notify) { struct callback_head *head; - unsigned long flags; do { head = READ_ONCE(task->task_works); @@ -42,17 +69,7 @@ task_work_add(struct task_struct *task, struct callback_head *work, int notify) set_notify_resume(task); break; case TWA_SIGNAL: - /* - * Only grab the sighand lock if we don't already have some - * task_work pending. This pairs with the smp_store_mb() - * in get_signal(), see comment there. - */ - if (!(READ_ONCE(task->jobctl) & JOBCTL_TASK_WORK) && - lock_task_sighand(task, &flags)) { - task->jobctl |= JOBCTL_TASK_WORK; - signal_wake_up(task, 0); - unlock_task_sighand(task, &flags); - } + task_work_notify_signal(task); break; } -- 2.28.0