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=-12.8 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=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 94CA7C4363A for ; Mon, 26 Oct 2020 20:32:50 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 3F2FD20709 for ; Mon, 26 Oct 2020 20:32:50 +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="rHPO5+VV" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1732192AbgJZUct (ORCPT ); Mon, 26 Oct 2020 16:32:49 -0400 Received: from mail-io1-f65.google.com ([209.85.166.65]:37267 "EHLO mail-io1-f65.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1732102AbgJZUcj (ORCPT ); Mon, 26 Oct 2020 16:32:39 -0400 Received: by mail-io1-f65.google.com with SMTP id q25so11831294ioh.4 for ; Mon, 26 Oct 2020 13:32:37 -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=WqNJgzUJ730nftaXzhmDP2PjcBlHnvqhfXXpoZKk+Cg=; b=rHPO5+VVrPfse+fV612DyhXyGzf2LsPDSv9jbH/n2+OtjYsIZZQ99L+5XyRWdOras1 xwr6Y049mpLLuYYTwAiLYjugjCp/Y8Gm8+wZqnBte95dw1RMPHOFj4gDLLlyTnJ0wtqK vr8kJUe7xpsGyxF8tHRMahnO8PQMDUFAcULaDaUw78txqMcYx6zUOLUuEqg/W32WFX2J 2QGNnozOFvMmD7XuPCfmq0w+nAzHgg4PYPpDXC/ZFOie8mqavk7S9AbmrPNFPy5QVRFp EMo9yR3jP2O173Rt5qd34B1146FlFGa9a/29UPsoPHST4NcU3T2WhqqDNibLoDcNTnwk C4Vg== 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=WqNJgzUJ730nftaXzhmDP2PjcBlHnvqhfXXpoZKk+Cg=; b=McHEEnG1mvG9Rxsa01RWwHyMJv41AzDG9+u8l9fQa7sA8l6KbpCLCdENMMaJNIh4on LTfcGh9D//NBRJBbm1/Ldj7FxsMHT/Vubdc36+soGIVeO2XLVlK9eiiM+Fhq/JNbVtor 9+cqWWS9gwFH1XniwUa0LKb/9VzmK0QWDAijp9vMWazhc3xYdGbVNQp41DIWdypkU8iU 9WPAcL4YvA9EWcYVH5BoylrZqoOUDeksDeiwS9aHqOwkYH7D1lB/6ZWmwBkwGcPGCtrL HNaUKcJ4G4W5KpC5zMhVC84nIY6jP1SMp34hEKnzGUB3xaoeX27GLojwW8rc0Hb4YxC4 uNTw== X-Gm-Message-State: AOAM5327wjLvLBeJ2RnoRTEr3neR/vILAXBlg03UDVLgwavd5ztmubv4 K4AXSOYlZjkYdksusImXN7DueA== X-Google-Smtp-Source: ABdhPJw7/DJO/4KNfjJqHXElP5SoVmaIK2Tj6PlGMYmDQjAPG1tc2o34EoVoUAdlIx4P+/LJPugmqw== X-Received: by 2002:a6b:92c6:: with SMTP id u189mr12162338iod.192.1603744357353; Mon, 26 Oct 2020 13:32:37 -0700 (PDT) Received: from p1.localdomain ([65.144.74.34]) by smtp.gmail.com with ESMTPSA id e12sm6770373ilq.65.2020.10.26.13.32.36 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 26 Oct 2020 13:32:36 -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: Mon, 26 Oct 2020 14:32:30 -0600 Message-Id: <20201026203230.386348-5-axboe@kernel.dk> X-Mailer: git-send-email 2.29.0 In-Reply-To: <20201026203230.386348-1-axboe@kernel.dk> References: <20201026203230.386348-1-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 Reviewed-by: Oleg Nesterov 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 8d6e1217c451..15b087286bea 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) +{ +#if defined(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 @@ -33,7 +61,6 @@ int task_work_add(struct task_struct *task, struct callback_head *work, enum task_work_notify_mode notify) { struct callback_head *head; - unsigned long flags; do { head = READ_ONCE(task->task_works); @@ -49,17 +76,7 @@ int task_work_add(struct task_struct *task, struct callback_head *work, 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; default: WARN_ON_ONCE(1); -- 2.29.0