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=-15.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER, INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED 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 DB127C4338F for ; Wed, 11 Aug 2021 12:26:34 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id BB4FE60F22 for ; Wed, 11 Aug 2021 12:26:34 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S237695AbhHKM04 (ORCPT ); Wed, 11 Aug 2021 08:26:56 -0400 Received: from Galois.linutronix.de ([193.142.43.55]:50874 "EHLO galois.linutronix.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S238391AbhHKMYS (ORCPT ); Wed, 11 Aug 2021 08:24:18 -0400 Message-ID: <20210811121418.181768544@linutronix.de> DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020; t=1628684634; 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: references:references; bh=BU+a69+6ahUqAFhsziSIuOkhY64ZRPFjxofuSmf1/Ac=; b=c40J4TZhei4jHzXVkjfi2hPPgxxIfdC9VVzWJkoSLRTqBDn0qRet7+8rW4axMsInhrcsYt ESHONGGQUo6iAbrvg6vD0npuT4oyYT4k9riCzHpSfMeZ1eTRd6r1NswmpJP99R90dx5s/k sla8QECWEeE0T99EoIhy2BdV9FZ8DAdmA5dKe+VD5vaDVjCu4WpSonm3aDdi+rEGFbgO/C /6ylA3sWVFHFcIR7xqJT7nXN6MQhlOJx69PfqdNeWE/X1DE5p659LSPj3NWbPe3w8JsXQL rJggw+yoTOFBNu60ZhMGAXkhbWHvlq7Fu34Ihhi7ftLONj3MJO8gpJhWMVuKTQ== DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020e; t=1628684634; 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: references:references; bh=BU+a69+6ahUqAFhsziSIuOkhY64ZRPFjxofuSmf1/Ac=; b=4nYnITFp9TEDBLhWcS+uA/BK12z92V6W+PKE/u4WRxLgmDDO/o8Tt9hHv0io7cn7EfdAz3 Qim13oImEkb8nYCw== From: Thomas Gleixner To: LKML Cc: Peter Zijlstra , Ingo Molnar , Juri Lelli , Steven Rostedt , Daniel Bristot de Oliveira , Will Deacon , Waiman Long , Boqun Feng , Sebastian Andrzej Siewior , Davidlohr Bueso , Mike Galbraith Subject: [patch V4 68/68] locking/rtmutex: Add adaptive spinwait mechanism References: <20210811120348.855823694@linutronix.de> MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-transfer-encoding: 8-bit Date: Wed, 11 Aug 2021 14:23:54 +0200 (CEST) Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Steven Rostedt Going to sleep when locks are contended can be quite inefficient when the contention time is short and the lock owner is running on a different CPU. The MCS mechanism cannot be used because MCS is strictly FIFO ordered while for rtmutex based locks the waiter ordering is priority based. Provide a simple adaptive spinwait mechanism which currently restricts the spinning to the top priority waiter. [ tglx: Provide a contemporary changelog, extended it to all rtmutex based locks and updated it to match the other spin on owner implementations ] Originally-by: Gregory Haskins Signed-off-by: Steven Rostedt Signed-off-by: Thomas Gleixner --- V4: Rename to rtmutex_spin_on_owner() (PeterZ) Check for top waiter changes and rewrite comment (Davidlohr) V3: Fold the extension for regular sleeping locks and add the missing spin wait checks (PeterZ) --- kernel/locking/rtmutex.c | 67 +++++++++++++++++++++++++++++++++++++++++++++-- 1 file changed, 65 insertions(+), 2 deletions(-) --- --- a/kernel/locking/rtmutex.c +++ b/kernel/locking/rtmutex.c @@ -8,6 +8,11 @@ * Copyright (C) 2005-2006 Timesys Corp., Thomas Gleixner * Copyright (C) 2005 Kihon Technologies Inc., Steven Rostedt * Copyright (C) 2006 Esben Nielsen + * Adaptive Spinlocks: + * Copyright (C) 2008 Novell, Inc., Gregory Haskins, Sven Dietrich, + * and Peter Morreale, + * Adaptive Spinlocks simplification: + * Copyright (C) 2008 Red Hat, Inc., Steven Rostedt * * See Documentation/locking/rt-mutex-design.rst for details. */ @@ -1297,6 +1302,52 @@ static __always_inline void __rt_mutex_u rt_mutex_slowunlock(lock); } +#ifdef CONFIG_SMP +static bool rtmutex_spin_on_owner(struct rt_mutex_base *lock, + struct rt_mutex_waiter *waiter, + struct task_struct *owner) +{ + bool res = true; + + rcu_read_lock(); + for (;;) { + /* If owner changed, trylock again. */ + if (owner != rt_mutex_owner(lock)) + break; + /* + * Ensure that @owner is dereferenced after checking that + * the lock owner still matches @owner. If that fails, + * @owner might point to freed memory. If it still matches, + * the rcu_read_lock() ensures the memory stays valid. + */ + barrier(); + /* + * Stop spinning when: + * - the lock owner has been scheduled out + * - current is not longer the top waiter + * - current is requested to reschedule (redundant + * for CONFIG_PREEMPT_RCU=y) + * - the VCPU on which owner runs is preempted + */ + if (!owner->on_cpu || waiter != rt_mutex_top_waiter(lock) || + need_resched() || vcpu_is_preempted(task_cpu(owner))) { + res = false; + break; + } + cpu_relax(); + } + rcu_read_unlock(); + return res; +} +#else +static bool rtmutex_spin_on_owner(struct rt_mutex_base *lock, + struct rt_mutex_waiter *waiter, + struct task_struct *owner) +{ + return false; +} +#endif + #ifdef RT_MUTEX_BUILD_MUTEX /* * Functions required for: @@ -1381,6 +1432,7 @@ static int __sched rt_mutex_slowlock_blo struct rt_mutex_waiter *waiter) { struct rt_mutex *rtm = container_of(lock, struct rt_mutex, rtmutex); + struct task_struct *owner; int ret = 0; for (;;) { @@ -1403,9 +1455,14 @@ static int __sched rt_mutex_slowlock_blo break; } + if (waiter == rt_mutex_top_waiter(lock)) + owner = rt_mutex_owner(lock); + else + owner = NULL; raw_spin_unlock_irq(&lock->wait_lock); - schedule(); + if (!owner || !rtmutex_spin_on_owner(lock, waiter, owner)) + schedule(); raw_spin_lock_irq(&lock->wait_lock); set_current_state(state); @@ -1561,6 +1618,7 @@ static __always_inline int __rt_mutex_lo static void __sched rtlock_slowlock_locked(struct rt_mutex_base *lock) { struct rt_mutex_waiter waiter; + struct task_struct *owner; lockdep_assert_held(&lock->wait_lock); @@ -1579,9 +1637,14 @@ static void __sched rtlock_slowlock_lock if (try_to_take_rt_mutex(lock, current, &waiter)) break; + if (&waiter == rt_mutex_top_waiter(lock)) + owner = rt_mutex_owner(lock); + else + owner = NULL; raw_spin_unlock_irq(&lock->wait_lock); - schedule_rtlock(); + if (!owner || !rtmutex_spin_on_owner(lock, &waiter, owner)) + schedule_rtlock(); raw_spin_lock_irq(&lock->wait_lock); set_current_state(TASK_RTLOCK_WAIT);