From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752023AbdLSUYy (ORCPT ); Tue, 19 Dec 2017 15:24:54 -0500 Received: from mga03.intel.com ([134.134.136.65]:48019 "EHLO mga03.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750825AbdLSUYw (ORCPT ); Tue, 19 Dec 2017 15:24:52 -0500 X-Amp-Result: SKIPPED(no attachment in message) X-Amp-File-Uploaded: False X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.45,428,1508828400"; d="scan'208";a="3700807" Subject: Re: [PATCH 2/4] perf/x86/intel: fix event update for auto-reload From: "Liang, Kan" To: Peter Zijlstra Cc: mingo@redhat.com, acme@kernel.org, linux-kernel@vger.kernel.org, tglx@linutronix.de, jolsa@redhat.com, eranian@google.com, ak@linux.intel.com References: <1513596891-12362-1-git-send-email-kan.liang@linux.intel.com> <1513596891-12362-3-git-send-email-kan.liang@linux.intel.com> <20171219185810.d4yqz6qwqmx3f5o5@hirez.programming.kicks-ass.net> Message-ID: Date: Tue, 19 Dec 2017 15:24:49 -0500 User-Agent: Mozilla/5.0 (Windows NT 10.0; WOW64; rv:52.0) Gecko/20100101 Thunderbird/52.5.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 12/19/2017 3:08 PM, Liang, Kan wrote: > > > On 12/19/2017 1:58 PM, Peter Zijlstra wrote: >> On Mon, Dec 18, 2017 at 03:34:49AM -0800, kan.liang@linux.intel.com >> wrote: >>>   arch/x86/events/core.c     | 14 ++++++++++++++ >>>   arch/x86/events/intel/ds.c |  8 +++++++- >>>   2 files changed, 21 insertions(+), 1 deletion(-) >>> >>> diff --git a/arch/x86/events/core.c b/arch/x86/events/core.c >>> index 35552ea..f74e21d 100644 >>> --- a/arch/x86/events/core.c >>> +++ b/arch/x86/events/core.c >>> @@ -100,6 +100,20 @@ u64 x86_perf_event_update(struct perf_event *event, >>>        * of the count. >>>        */ >>>       delta = (new_raw_count << shift) - (prev_raw_count << shift); >>> + >>> +    /* >>> +     * Take auto-reload into account >>> +     * For the auto-reload before the last time, it went through the >>> +     * whole period (reload_val) every time. >>> +     * Just simply add period * times to the event. >>> +     * >>> +     * For the last load, the elapsed delta (event-)time need to be >>> +     * corrected by adding the period. Because the start point is >>> -period. >>> +     */ >>> +    if (reload_times > 0) { >>> +        delta += (reload_val << shift); >>> +        local64_add(reload_val * (reload_times - 1), &event->count); >>> +    } >>>       delta >>= shift; >>>       local64_add(delta, &event->count); >>> diff --git a/arch/x86/events/intel/ds.c b/arch/x86/events/intel/ds.c >>> index 0b693b7..f0f6026 100644 >>> --- a/arch/x86/events/intel/ds.c >>> +++ b/arch/x86/events/intel/ds.c >>> @@ -1256,11 +1256,17 @@ static void __intel_pmu_pebs_event(struct >>> perf_event *event, >>>                      void *base, void *top, >>>                      int bit, int count) >>>   { >>> +    struct hw_perf_event *hwc = &event->hw; >>>       struct perf_sample_data data; >>>       struct pt_regs regs; >>>       void *at = get_next_pebs_record_by_bit(base, top, bit); >>> -    if (!intel_pmu_save_and_restart(event, 0, 0) && >>> +    /* >>> +     * Now, auto-reload is only enabled in fixed period mode. >>> +     * The reload value is always hwc->sample_period. >>> +     * May need to change it, if auto-reload is enabled in freq mode >>> later. >>> +     */ >>> +    if (!intel_pmu_save_and_restart(event, hwc->sample_period, count >>> - 1) && >>>           !(event->hw.flags & PERF_X86_EVENT_AUTO_RELOAD)) >>>           return; >> >> This all looks very wrong... In auto reload we should never call >> intel_pmu_save_and_restore() in the first place I think. >> >> Things like x86_perf_event_update() and x86_perf_event_set_period() >> simply _cannot_ do the right thing when we auto reload the counter. >> > > I think it should be OK to call it in first place. > For x86_perf_event_update(), the reload_times will tell if it's auto > reload. Both period_left and event->count are carefully recalculated for > auto reload. Think a bit more. You are right. We cannot rely on count to tell us if it's auto reload. The count could also be 1 if auto reload is enabled. I will fix it in V2. Thanks, Kan > For x86_perf_event_set_period(), there is nothing special needed for > auto reload. The period is fixed. The period_left from > x86_perf_event_update() is already handled. > > > BTW: It should be 'count' not 'count - 1' which pass to > intel_pmu_save_and_restart(). I just found the issue. I will fix it in > V2 with other improvements if there are any. > > Thanks, > Kan > >