From patchwork Wed Dec 21 18:46:36 2016 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Patchwork-Submitter: =?utf-8?q?Nicolai_H=C3=A4hnle?= X-Patchwork-Id: 9483665 Return-Path: Received: from mail.wl.linuxfoundation.org (pdx-wl-mail.web.codeaurora.org [172.30.200.125]) by pdx-korg-patchwork.web.codeaurora.org (Postfix) with ESMTP id A55F3601D3 for ; Wed, 21 Dec 2016 18:48:50 +0000 (UTC) Received: from mail.wl.linuxfoundation.org (localhost [127.0.0.1]) by mail.wl.linuxfoundation.org (Postfix) with ESMTP id 95BB027F9E for ; Wed, 21 Dec 2016 18:48:50 +0000 (UTC) Received: by mail.wl.linuxfoundation.org (Postfix, from userid 486) id 8829B28424; Wed, 21 Dec 2016 18:48:50 +0000 (UTC) X-Spam-Checker-Version: SpamAssassin 3.3.1 (2010-03-16) on pdx-wl-mail.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-4.1 required=2.0 tests=BAYES_00, DKIM_ADSP_CUSTOM_MED, DKIM_SIGNED, FREEMAIL_FROM, RCVD_IN_DNSWL_MED, T_DKIM_INVALID autolearn=ham version=3.3.1 Received: from gabe.freedesktop.org (gabe.freedesktop.org [131.252.210.177]) (using TLSv1.2 with cipher DHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.wl.linuxfoundation.org (Postfix) with ESMTPS id 1C17B27F9E for ; Wed, 21 Dec 2016 18:48:50 +0000 (UTC) Received: from gabe.freedesktop.org (localhost [127.0.0.1]) by gabe.freedesktop.org (Postfix) with ESMTP id CF6C36F0D3; Wed, 21 Dec 2016 18:48:48 +0000 (UTC) X-Original-To: dri-devel@lists.freedesktop.org Delivered-To: dri-devel@lists.freedesktop.org Received: from mail-wm0-x241.google.com (mail-wm0-x241.google.com [IPv6:2a00:1450:400c:c09::241]) by gabe.freedesktop.org (Postfix) with ESMTPS id 59F726E0F0 for ; Wed, 21 Dec 2016 18:46:58 +0000 (UTC) Received: by mail-wm0-x241.google.com with SMTP id l2so6523922wml.2 for ; Wed, 21 Dec 2016 10:46:58 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=from:to:cc:subject:date:message-id:in-reply-to:references :mime-version:content-transfer-encoding; bh=FYuzMqk9oUoLFd1EzGLrIvmiSo4Cjfn7pX9SOW1ptvk=; b=WoqhXmCnlTitMyl6RRqQvM9ACLkB3ZkTIF0JoReaAFJPePtMenBEXCNksfeijg8PSW FiRx0vtWBBeLCRmwqBFtHB6gkCvZPsyxgPwiOXzA/TCll04rRBo5xwDqPcC0gBQF4Cr3 U8jJ5VoSdY0yeMiBRIGjqxOQElQd0Q5OM7Y5qa8z98tyaVH0RjcJAL2uPdNOPBinXGk2 3ZsqiQD6cQbd7Jz/wypge45E9crxqJkJmjimTlCN/l5so2GB9Ym8V6hcabAI4FQPuKHE zvN3Moen0nLN0Zjciu/MgajbA4u3gQAAsJ07no3ohEOA/1Ve2Gu69pOSLlM6l1cqmIm+ aPWA== 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=FYuzMqk9oUoLFd1EzGLrIvmiSo4Cjfn7pX9SOW1ptvk=; b=h0yewayGPc+ZE6cJK0BAWEEwob5uj7TRH7393/hoGIeqzRo5pvcdg9aotMuVPrVdsI PAwb0mYklDrDOVdjvWFXOp+zThJ2td4D9JfTbKiFhyJwguw4KEZFN2ilID4QulO2O0x9 a+Bi24SOcbDmn8PPgksOV6lD+cwBNJF1V/Tio4WMo3qwa9javtOhglaenxfHzkX3+xKP zq9jv/Usme7rb9VBvkfZiCYFRR1SDSzY0Sah4n51F0I4Jz/X4BhqhVuVm/NDwDirSlco yyfMCWSB8WQCwaoHzT4jDjagUSee147/R/f7JPo5tTflYx7fvTqcRR9svNgLyFZ/+XRk 1yNg== X-Gm-Message-State: AIkVDXJHR3hIs5YHhylO57EWWjQvfquQ1tGWfhYSkBXqAWh2De10HFP+wQtvcrUl0SOMMQ== X-Received: by 10.28.147.204 with SMTP id v195mr797080wmd.35.1482346016602; Wed, 21 Dec 2016 10:46:56 -0800 (PST) Received: from cassiopeia.fritz.box ([2001:a61:110a:1701:2511:6687:1ba5:b45b]) by smtp.gmail.com with ESMTPSA id ke6sm31840526wjb.21.2016.12.21.10.46.55 (version=TLS1_2 cipher=ECDHE-RSA-AES128-SHA bits=128/128); Wed, 21 Dec 2016 10:46:56 -0800 (PST) From: =?UTF-8?q?Nicolai=20H=C3=A4hnle?= To: linux-kernel@vger.kernel.org Subject: [PATCH v3 08/12] locking/ww_mutex: Wake at most one waiter for back off when acquiring the lock Date: Wed, 21 Dec 2016 19:46:36 +0100 Message-Id: <1482346000-9927-9-git-send-email-nhaehnle@gmail.com> X-Mailer: git-send-email 2.7.4 In-Reply-To: <1482346000-9927-1-git-send-email-nhaehnle@gmail.com> References: <1482346000-9927-1-git-send-email-nhaehnle@gmail.com> MIME-Version: 1.0 Cc: Maarten Lankhorst , =?UTF-8?q?Nicolai=20H=C3=A4hnle?= , Peter Zijlstra , dri-devel@lists.freedesktop.org, Ingo Molnar X-BeenThere: dri-devel@lists.freedesktop.org X-Mailman-Version: 2.1.18 Precedence: list List-Id: Direct Rendering Infrastructure - Development List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: dri-devel-bounces@lists.freedesktop.org Sender: "dri-devel" X-Virus-Scanned: ClamAV using ClamSMTP From: Nicolai Hähnle The wait list is sorted by stamp order, and the only waiting task that may have to back off is the first waiter with a context. The regular slow path does not have to wake any other tasks at all, since all other waiters that would have to back off were either woken up when the waiter was added to the list, or detected the condition before they added themselves. Median timings taken of a contention-heavy GPU workload: Without this series: real 0m59.900s user 0m7.516s sys 2m16.076s With changes up to and including this patch: real 0m52.946s user 0m7.272s sys 1m55.964s Cc: Peter Zijlstra Cc: Ingo Molnar Cc: Maarten Lankhorst Cc: Daniel Vetter Cc: Chris Wilson Cc: dri-devel@lists.freedesktop.org Signed-off-by: Nicolai Hähnle --- kernel/locking/mutex.c | 58 +++++++++++++++++++++++++++++++++----------------- 1 file changed, 39 insertions(+), 19 deletions(-) diff --git a/kernel/locking/mutex.c b/kernel/locking/mutex.c index ee4d152..c3f70dd 100644 --- a/kernel/locking/mutex.c +++ b/kernel/locking/mutex.c @@ -285,6 +285,35 @@ __ww_ctx_stamp_after(struct ww_acquire_ctx *a, struct ww_acquire_ctx *b) } /* + * Wake up any waiters that may have to back off when the lock is held by the + * given context. + * + * Due to the invariants on the wait list, this can only affect the first + * waiter with a context. + * + * Must be called with wait_lock held. The current task must not be on the + * wait list. + */ +static void __sched +__ww_mutex_wakeup_for_backoff(struct mutex *lock, struct ww_acquire_ctx *ww_ctx) +{ + struct mutex_waiter *cur; + + list_for_each_entry(cur, &lock->wait_list, list) { + if (!cur->ww_ctx) + continue; + + if (cur->ww_ctx->acquired > 0 && + __ww_ctx_stamp_after(cur->ww_ctx, ww_ctx)) { + debug_mutex_wake_waiter(lock, cur); + wake_up_process(cur->task); + } + + break; + } +} + +/* * After acquiring lock with fastpath or when we lost out in contested * slowpath, set ctx and wake up any waiters so they can recheck. */ @@ -293,7 +322,6 @@ ww_mutex_set_context_fastpath(struct ww_mutex *lock, struct ww_acquire_ctx *ctx) { unsigned long flags; - struct mutex_waiter *cur; ww_mutex_lock_acquired(lock, ctx); @@ -319,16 +347,15 @@ ww_mutex_set_context_fastpath(struct ww_mutex *lock, * so they can see the new lock->ctx. */ spin_lock_mutex(&lock->base.wait_lock, flags); - list_for_each_entry(cur, &lock->base.wait_list, list) { - debug_mutex_wake_waiter(&lock->base, cur); - wake_up_process(cur->task); - } + __ww_mutex_wakeup_for_backoff(&lock->base, ctx); spin_unlock_mutex(&lock->base.wait_lock, flags); } /* - * After acquiring lock in the slowpath set ctx and wake up any - * waiters so they can recheck. + * After acquiring lock in the slowpath set ctx. + * + * Unlike for the fast path, the caller ensures that waiters are woken up where + * necessary. * * Callers must hold the mutex wait_lock. */ @@ -336,19 +363,8 @@ static __always_inline void ww_mutex_set_context_slowpath(struct ww_mutex *lock, struct ww_acquire_ctx *ctx) { - struct mutex_waiter *cur; - ww_mutex_lock_acquired(lock, ctx); lock->ctx = ctx; - - /* - * Give any possible sleeping processes the chance to wake up, - * so they can recheck if they have to back off. - */ - list_for_each_entry(cur, &lock->base.wait_list, list) { - debug_mutex_wake_waiter(&lock->base, cur); - wake_up_process(cur->task); - } } #ifdef CONFIG_MUTEX_SPIN_ON_OWNER @@ -726,8 +742,12 @@ __mutex_lock_common(struct mutex *lock, long state, unsigned int subclass, /* * After waiting to acquire the wait_lock, try again. */ - if (__mutex_trylock(lock, false)) + if (__mutex_trylock(lock, false)) { + if (use_ww_ctx && ww_ctx) + __ww_mutex_wakeup_for_backoff(lock, ww_ctx); + goto skip_wait; + } debug_mutex_lock_common(lock, &waiter); debug_mutex_add_waiter(lock, &waiter, task);