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 50571C4338F for ; Thu, 5 Aug 2021 15:46:24 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 37C6460F10 for ; Thu, 5 Aug 2021 15:46:24 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S242810AbhHEPqh (ORCPT ); Thu, 5 Aug 2021 11:46:37 -0400 Received: from Galois.linutronix.de ([193.142.43.55]:44554 "EHLO galois.linutronix.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S242478AbhHEPm7 (ORCPT ); Thu, 5 Aug 2021 11:42:59 -0400 Message-ID: <20210805153956.507589092@linutronix.de> DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020; t=1628178164; 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=sZ+ArfnpGIkqlgpVaQdtCxQn6qTi++uYQ5vC8P1LMNY=; b=qyo7oFkhGf10jQKCdW214exzWBTfr9gF5IVWmMf37jJ5Lmv02PZxwsmUfaffTO1mcV4D/z jkUSoql0gtnqJo836833mDfH/eCR+HMktftHao3nWCY9fq8B543fSNnSLiixlIjuMK+eKe 3/4AEwCOKkpve/5gG788PDcjsvGTP3pr64QYfkV8oW66QpAb3f4poDVoDaEtsp4nx/OzB+ 95CDQqBdlol6igvxBf/PNc0NxDNJMWJn8kZDrCCYQtsBl5WNbmWmma4ckYhuZ5dAVjNnBC Ug+nmjRcdvg6FrSOljPJxXCiGRJ08kRMSj1etrzMxs8sLVSxiy+7PQeQ4bEodg== DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020e; t=1628178164; 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=sZ+ArfnpGIkqlgpVaQdtCxQn6qTi++uYQ5vC8P1LMNY=; b=Bp9otr7/k1+E1O+XIZmu+pXJBwo4Bnp17H7btedDMDs59TzdCUFnV+v3ZBXE7ypj6gkLmM oRh5IYgqFHrJKjDg== Date: Thu, 05 Aug 2021 17:14:04 +0200 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 V3 64/64] locking/rtmutex: Add adaptive spinwait mechanism References: <20210805151300.330412127@linutronix.de> MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-transfer-encoding: 8-bit 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 ] Originally-by: Gregory Haskins Signed-off-by: Steven Rostedt Signed-off-by: Thomas Gleixner --- V3: Fold the extension for regular sleeping locks and add the missing spin wait checks (PeterZ) --- kernel/locking/rtmutex.c | 59 +++++++++++++++++++++++++++++++++++++++++++++-- 1 file changed, 57 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. */ @@ -1278,6 +1283,44 @@ static __always_inline void __rt_mutex_u rt_mutex_slowunlock(lock); } +#ifdef CONFIG_SMP +/* + * Note that owner is a speculative pointer and dereferencing relies + * on rcu_read_lock() and the check against the lock owner. + */ +static bool rtmutex_adaptive_spinwait(struct rt_mutex_base *lock, + struct task_struct *owner) +{ + bool res = true; + + rcu_read_lock(); + for (;;) { + /* Owner changed. Trylock again */ + if (owner != rt_mutex_owner(lock)) + break; + /* + * Ensure that owner->on_cpu is dereferenced _after_ + * checking the above to be valid. + */ + barrier(); + if (!owner->on_cpu || need_resched() || + vcpu_is_preempted(task_cpu(owner))) { + res = false; + break; + } + cpu_relax(); + } + rcu_read_unlock(); + return res; +} +#else +static bool rtmutex_adaptive_spinwait(struct rt_mutex_base *lock, + struct task_struct *owner) +{ + return false; +} +#endif + #ifdef RT_MUTEX_BUILD_MUTEX /* * Functions required for: @@ -1362,6 +1405,7 @@ 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 (;;) { @@ -1384,9 +1428,14 @@ 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_adaptive_spinwait(lock, owner)) + schedule(); raw_spin_lock_irq(&lock->wait_lock); set_current_state(state); @@ -1542,6 +1591,7 @@ 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); @@ -1560,9 +1610,14 @@ 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_adaptive_spinwait(lock, owner)) + schedule_rtlock(); raw_spin_lock_irq(&lock->wait_lock); set_current_state(TASK_RTLOCK_WAIT);