Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753661AbaBERzn (ORCPT ); Wed, 5 Feb 2014 12:55:43 -0500 Received: from merlin.infradead.org ([205.233.59.134]:55367 "EHLO merlin.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753116AbaBERzk (ORCPT ); Wed, 5 Feb 2014 12:55:40 -0500 Date: Wed, 5 Feb 2014 18:55:28 +0100 From: Peter Zijlstra To: Stephane Eranian Cc: "Yan, Zheng" , LKML , Ingo Molnar , Arnaldo Carvalho de Melo , Andi Kleen Subject: Re: [PATCH 06/14] perf, core: always switch pmu specific data during context switch Message-ID: <20140205175528.GF5002@laptop.programming.kicks-ass.net> References: <1388728091-18564-1-git-send-email-zheng.z.yan@intel.com> <1388728091-18564-7-git-send-email-zheng.z.yan@intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: 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 Wed, Feb 05, 2014 at 06:19:27PM +0100, Stephane Eranian wrote: > On Fri, Jan 3, 2014 at 6:48 AM, Yan, Zheng wrote: > > If two tasks were both forked from the same parent task, Events in their perf > > task contexts can be the same. Perf core optimizes context switch oout in this > > case. > > > > Previous patch inroduces pmu specific data. The data is task specific, so we > > should switch the data even when context switch is optimized out. > > > Reviwed-by: Stephane Eranian You should look again.. that xchg() is an atomic op and a total waste of time since the assignment back onto ctx->task_ctx_data is non-atomic. Complete fail there. > > Signed-off-by: Yan, Zheng > > --- > > kernel/events/core.c | 2 ++ > > 1 file changed, 2 insertions(+) > > > > diff --git a/kernel/events/core.c b/kernel/events/core.c > > index b6650ab..d6d8dea 100644 > > --- a/kernel/events/core.c > > +++ b/kernel/events/core.c > > @@ -2319,6 +2319,8 @@ static void perf_event_context_sched_out(struct task_struct *task, int ctxn, > > next->perf_event_ctxp[ctxn] = ctx; > > ctx->task = next; > > next_ctx->task = task; > > + ctx->task_ctx_data = xchg(&next_ctx->task_ctx_data, > > + ctx->task_ctx_data); > > do_switch = 0; > > > > perf_event_sync_stat(ctx, next_ctx); > > -- > > 1.8.4.2 > > -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/