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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 412D5C433FE for ; Mon, 28 Mar 2022 17:49:14 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S240875AbiC1Rux (ORCPT ); Mon, 28 Mar 2022 13:50:53 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:52620 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S238979AbiC1Rux (ORCPT ); Mon, 28 Mar 2022 13:50:53 -0400 Received: from mail-lj1-f176.google.com (mail-lj1-f176.google.com [209.85.208.176]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 01D0B3C4B7; Mon, 28 Mar 2022 10:49:12 -0700 (PDT) Received: by mail-lj1-f176.google.com with SMTP id a30so12799584ljq.13; Mon, 28 Mar 2022 10:49:11 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc; bh=EyQ8IXVuGy+MjhTeeviL9/NWr5Oku+oE3kNpUwAlM28=; b=mzUsrqs1v9Oox0FLiZXA0oFdHuqoEo4Bzxx8RTE8IW2/gN/kMRw5hJyIY1cmLV6Vch b6Nuh4yNiUtWICDHF+U+Xi7w19MAMZYQopDF/k/64vSbPj2J08FkzE1YDipEaOJdrHwp i+7eYODLfGrZRKcuVHHvxaO+HAVbX1MsVmpewDujMWBFaIHgdYaKrEJZC4ZFAr7k8t9X hFVDpYaLKnGJsiG8kU0DmOQoHIU5kS2DLvZY89xpazFhW6uNRSc9fd28pfIeFJrlerbB U/r3suyr+U/rD0SEZ0uJV4lF0txJxYuDjEbQGfgMglFrMVwOqvk0Wlkxo9mj4Z9ctItd gKJQ== X-Gm-Message-State: AOAM531oqij7enAauyfowhgvcSv9RMgJUMYpCgsdQYG0i3mSfBFW9g8W MaPas58lBD2uy/kRC2pGlmPcRXaile2sd4wAM40= X-Google-Smtp-Source: ABdhPJylsb5/U29MfMdIeOIKZdvUSIE4MIawm5G11yaSRrZfEr1IXA3xAF9bfyuvUtx6BVZVZ6Fg7r4xnLNf7VJDTG4= X-Received: by 2002:a05:651c:248:b0:245:5b3d:9abb with SMTP id x8-20020a05651c024800b002455b3d9abbmr21451205ljn.366.1648489750323; Mon, 28 Mar 2022 10:49:10 -0700 (PDT) MIME-Version: 1.0 References: <20220322185709.141236-1-namhyung@kernel.org> <20220322185709.141236-3-namhyung@kernel.org> <20220328113946.GA8939@worktop.programming.kicks-ass.net> In-Reply-To: <20220328113946.GA8939@worktop.programming.kicks-ass.net> From: Namhyung Kim Date: Mon, 28 Mar 2022 10:48:59 -0700 Message-ID: Subject: Re: [PATCH 2/2] locking: Apply contention tracepoints in the slow path To: Peter Zijlstra Cc: Ingo Molnar , Will Deacon , Waiman Long , Boqun Feng , LKML , Thomas Gleixner , Steven Rostedt , Byungchul Park , "Paul E. McKenney" , Mathieu Desnoyers , Arnd Bergmann , Radoslaw Burny , linux-arch , bpf , Hyeonggon Yoo <42.hyeyoo@gmail.com> Content-Type: text/plain; charset="UTF-8" Precedence: bulk List-ID: X-Mailing-List: bpf@vger.kernel.org On Mon, Mar 28, 2022 at 4:39 AM Peter Zijlstra wrote: > > On Tue, Mar 22, 2022 at 11:57:09AM -0700, Namhyung Kim wrote: > > diff --git a/kernel/locking/mutex.c b/kernel/locking/mutex.c > > index ee2fd7614a93..c88deda77cf2 100644 > > --- a/kernel/locking/mutex.c > > +++ b/kernel/locking/mutex.c > > @@ -644,6 +644,7 @@ __mutex_lock_common(struct mutex *lock, unsigned int state, unsigned int subclas > > } > > > > set_current_state(state); > > + trace_contention_begin(lock, 0); > > for (;;) { > > bool first; > > > > @@ -710,6 +711,7 @@ __mutex_lock_common(struct mutex *lock, unsigned int state, unsigned int subclas > > skip_wait: > > /* got the lock - cleanup and rejoice! */ > > lock_acquired(&lock->dep_map, ip); > > + trace_contention_end(lock, 0); > > > > if (ww_ctx) > > ww_mutex_lock_acquired(ww, ww_ctx); > > (note: it's possible to get to this trace_contention_end() without ever > having passed a _begin -- fixed in the below) > > > @@ -721,6 +723,7 @@ __mutex_lock_common(struct mutex *lock, unsigned int state, unsigned int subclas > > err: > > __set_current_state(TASK_RUNNING); > > __mutex_remove_waiter(lock, &waiter); > > + trace_contention_end(lock, ret); > > err_early_kill: > > raw_spin_unlock(&lock->wait_lock); > > debug_mutex_free_waiter(&waiter); > > > So there was one thing here, that might or might not be important, but > is somewhat inconsistent with the whole thing. That is, do you want to > include optimistic spinning in the contention time or not? Yes, this was in a grey area and would create begin -> begin -> end path for mutexes. But I think tools can handle it with the flags. > > Because currently you do it sometimes. > > Also, if you were to add LCB_F_MUTEX then you could have something like: Yep, I'm ok with having the mutex flag. Do you want me to send v5 with this change or would you like to do it by yourself? Thanks, Namhyung > > > --- a/kernel/locking/mutex.c > +++ b/kernel/locking/mutex.c > @@ -602,12 +602,14 @@ __mutex_lock_common(struct mutex *lock, > preempt_disable(); > mutex_acquire_nest(&lock->dep_map, subclass, 0, nest_lock, ip); > > + trace_contention_begin(lock, LCB_F_MUTEX | LCB_F_SPIN); > if (__mutex_trylock(lock) || > mutex_optimistic_spin(lock, ww_ctx, NULL)) { > /* got the lock, yay! */ > lock_acquired(&lock->dep_map, ip); > if (ww_ctx) > ww_mutex_set_context_fastpath(ww, ww_ctx); > + trace_contention_end(lock, 0); > preempt_enable(); > return 0; > } > @@ -644,7 +646,7 @@ __mutex_lock_common(struct mutex *lock, > } > > set_current_state(state); > - trace_contention_begin(lock, 0); > + trace_contention_begin(lock, LCB_F_MUTEX); > for (;;) { > bool first; > > @@ -684,10 +686,16 @@ __mutex_lock_common(struct mutex *lock, > * state back to RUNNING and fall through the next schedule(), > * or we must see its unlock and acquire. > */ > - if (__mutex_trylock_or_handoff(lock, first) || > - (first && mutex_optimistic_spin(lock, ww_ctx, &waiter))) > + if (__mutex_trylock_or_handoff(lock, first)) > break; > > + if (first) { > + trace_contention_begin(lock, LCB_F_MUTEX | LCB_F_SPIN); > + if (mutex_optimistic_spin(lock, ww_ctx, &waiter)) > + break; > + trace_contention_begin(lock, LCB_F_MUTEX); > + } > + > raw_spin_lock(&lock->wait_lock); > } > raw_spin_lock(&lock->wait_lock); > @@ -723,8 +731,8 @@ __mutex_lock_common(struct mutex *lock, > err: > __set_current_state(TASK_RUNNING); > __mutex_remove_waiter(lock, &waiter); > - trace_contention_end(lock, ret); > err_early_kill: > + trace_contention_end(lock, ret); > raw_spin_unlock(&lock->wait_lock); > debug_mutex_free_waiter(&waiter); > mutex_release(&lock->dep_map, ip);