From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751934Ab3GEFg1 (ORCPT ); Fri, 5 Jul 2013 01:36:27 -0400 Received: from mga01.intel.com ([192.55.52.88]:40035 "EHLO mga01.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751062Ab3GEFg0 (ORCPT ); Fri, 5 Jul 2013 01:36:26 -0400 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="4.87,1000,1363158000"; d="scan'208";a="360796163" Message-ID: <51D65B58.1050201@intel.com> Date: Fri, 05 Jul 2013 13:36:24 +0800 From: "Yan, Zheng" User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:17.0) Gecko/20130514 Thunderbird/17.0.6 MIME-Version: 1.0 To: Peter Zijlstra CC: linux-kernel@vger.kernel.org, mingo@kernel.org, eranian@google.com, andi@firstfloor.org Subject: Re: [PATCH v2 4/7] perf, x86: Save/resotre LBR stack during context switch References: <1372663387-11754-1-git-send-email-zheng.z.yan@intel.com> <1372663387-11754-5-git-send-email-zheng.z.yan@intel.com> <20130704124536.GK23916@twins.programming.kicks-ass.net> In-Reply-To: <20130704124536.GK23916@twins.programming.kicks-ass.net> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 07/04/2013 08:45 PM, Peter Zijlstra wrote: > On Mon, Jul 01, 2013 at 03:23:04PM +0800, Yan, Zheng wrote: > >> @@ -2488,25 +2508,31 @@ static void perf_branch_stack_sched_in(struct task_struct *prev, >> >> list_for_each_entry_rcu(pmu, &pmus, entry) { >> cpuctx = this_cpu_ptr(pmu->pmu_cpu_context); >> + task_ctx = cpuctx->task_ctx; >> >> /* >> - * check if the context has at least one >> - * event using PERF_SAMPLE_BRANCH_STACK >> + * force flush the branch stack if there are cpu-wide events >> + * using PERF_SAMPLE_BRANCH_STACK >> + * >> + * save/restore the branch stack if the task context has >> + * at least one event using PERF_SAMPLE_BRANCH_STACK >> */ >> - if (cpuctx->ctx.nr_branch_stack > 0 >> - && pmu->flush_branch_stack) { >> - >> + bool force_flush = cpuctx->ctx.nr_branch_stack > 0; >> + if (pmu->branch_stack_sched && >> + (force_flush || >> + (task_ctx && task_ctx->nr_branch_stack > 0))) { >> pmu = cpuctx->ctx.pmu; >> >> - perf_ctx_lock(cpuctx, cpuctx->task_ctx); >> + perf_ctx_lock(cpuctx, task_ctx); >> >> perf_pmu_disable(pmu); >> >> - pmu->flush_branch_stack(); >> + pmu->branch_stack_sched(task_ctx, >> + sched_in, force_flush); >> >> perf_pmu_enable(pmu); >> >> - perf_ctx_unlock(cpuctx, cpuctx->task_ctx); >> + perf_ctx_unlock(cpuctx, task_ctx); >> } >> } >> > > I never really like this; and yes I know I wrote part of that. Is there > any way we can get rid of this and to it 'properly' through the events > that get scheduled? > > After all; the LBR usage is through the events, so scheduling the events > should also manage the LBR state. > > What is missing for that to work? > the LBR is shared resource, can be used by multiple events at the same time. Strictly speaking，LBR is associated with task, not event. One example is there are 5 events using the LBR stack feature, but there are only 4 counters. So these events need schedule. Saving/restoring LBR on the basis of event is clearly wrong. Regards Yan, Zheng