From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753086AbaBJSKc (ORCPT ); Mon, 10 Feb 2014 13:10:32 -0500 Received: from merlin.infradead.org ([205.233.59.134]:56230 "EHLO merlin.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752526AbaBJSKb (ORCPT ); Mon, 10 Feb 2014 13:10:31 -0500 Date: Mon, 10 Feb 2014 19:10:26 +0100 From: Peter Zijlstra To: Mark Rutland Cc: linux-kernel@vger.kernel.org, will.deacon@arm.com, dave.martin@arm.com, Ingo Molnar Subject: Re: [PATCH 7/7] perf: kill perf_event_context::pmu Message-ID: <20140210181026.GD27965@twins.programming.kicks-ass.net> References: <1392054264-23570-1-git-send-email-mark.rutland@arm.com> <1392054264-23570-8-git-send-email-mark.rutland@arm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1392054264-23570-8-git-send-email-mark.rutland@arm.com> User-Agent: Mutt/1.5.21 (2012-12-30) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Feb 10, 2014 at 05:44:24PM +0000, Mark Rutland wrote: > Currently portions of the perf subsystem assume that a > perf_event_context is associated with a single pmu while in reality a > single perf_event_context may be shared by a number of pmus, as commit > 443772776c69 (perf: Disable all pmus on unthrottling and rescheduling) > describes. > > This patch removes perf_event_context::pmu, replacing it with a direct > pointer to the associated perf_cpu_context and a task_ctx_nr (as all > pmus sharing a context have the same task_ctx_nr). This makes the > relationship between pmus and perf_event_contexts clearer and allows us > to save on some pointer chasing. > > This also fixes a potential misuse of ctx->pmu introduced in commit > bad7192b842c (perf: Fix PERF_EVENT_IOC_PERIOD to force-reset the > period), where ctx->pmu is disabled before modifying state on > event->pmu. In this case the two pmus are not guaranteed to be the same. > > As perf_pmu_rotate_{start,stop} only really care about the context they > are rotating, they are renamed to perf_event_ctx_{start,stop}. This very much relies on the previous patch where you make pmu_disable iterate all the events. We could also change this to keep a pmu list for each context and iterate that instead. Given there is indeed a fair limit on different PMUs in the system that iteration should be much shorter.