From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754643AbbLKPRh (ORCPT ); Fri, 11 Dec 2015 10:17:37 -0500 Received: from mga14.intel.com ([192.55.52.115]:9877 "EHLO mga14.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753977AbbLKPRe (ORCPT ); Fri, 11 Dec 2015 10:17:34 -0500 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.20,414,1444719600"; d="scan'208";a="858856720" From: Alexander Shishkin To: Peter Zijlstra Cc: Ingo Molnar , linux-kernel@vger.kernel.org, vince@deater.net, eranian@google.com, Arnaldo Carvalho de Melo , Mathieu Poirier Subject: Re: [PATCH v0 3/5] perf: Introduce instruction trace filtering In-Reply-To: <20151211150011.GT6356@twins.programming.kicks-ass.net> References: <1449840998-29902-1-git-send-email-alexander.shishkin@linux.intel.com> <1449840998-29902-4-git-send-email-alexander.shishkin@linux.intel.com> <20151211150011.GT6356@twins.programming.kicks-ass.net> User-Agent: Notmuch/0.21 (http://notmuchmail.org) Emacs/24.5.1 (x86_64-pc-linux-gnu) Date: Fri, 11 Dec 2015 17:17:25 +0200 Message-ID: <871tatc8vu.fsf@ashishki-desk.ger.corp.intel.com> MIME-Version: 1.0 Content-Type: text/plain Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Peter Zijlstra writes: > On Fri, Dec 11, 2015 at 03:36:36PM +0200, Alexander Shishkin wrote: >> +static int __perf_event_itrace_filters_setup(void *info) >> +{ >> + struct perf_event *event = info; >> + int ret; >> + >> + if (READ_ONCE(event->state) != PERF_EVENT_STATE_ACTIVE) >> + return -EAGAIN; >> + >> + /* matches smp_wmb() in event_sched_in() */ >> + smp_rmb(); >> + >> + /* >> + * There is a window with interrupts enabled before we get here, >> + * so we need to check again lest we try to stop another cpu's event. >> + */ >> + if (READ_ONCE(event->oncpu) != smp_processor_id()) >> + return -EAGAIN; >> + >> + event->pmu->stop(event, PERF_EF_UPDATE); >> + rcu_read_lock(); >> + ret = event->pmu->itrace_filter_setup(event); >> + rcu_read_unlock(); >> + event->pmu->start(event, PERF_EF_RELOAD); > > Would it not be more sensible to let the ::itrace_filter_setup() method > do the stop/start-ing if and when needed? I don't have a strong opinion on this, the only question is, are we comfortable with pmu driver callback doing the rcu_read_lock/unlock, because it still needs to iterate the filter list. Other than that it's probably a good idea. Thanks, -- Alex