From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-13.0 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI,NICE_REPLY_A, SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id AB34CC433E0 for ; Tue, 4 Aug 2020 07:07:26 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id BA5922076C for ; Tue, 4 Aug 2020 07:07:26 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728064AbgHDHHZ (ORCPT ); Tue, 4 Aug 2020 03:07:25 -0400 Received: from mga17.intel.com ([192.55.52.151]:58093 "EHLO mga17.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725904AbgHDHHY (ORCPT ); Tue, 4 Aug 2020 03:07:24 -0400 IronPort-SDR: pJ3dT/4dtQdX7R/WpTPn8Tr1yy6NIOE1BUB7ey3ug50AIjCXOO+WzDhRomFIvNLhW9uaCYl2Px g14dKSTgdvCA== X-IronPort-AV: E=McAfee;i="6000,8403,9702"; a="132322612" X-IronPort-AV: E=Sophos;i="5.75,433,1589266800"; d="scan'208";a="132322612" X-Amp-Result: SKIPPED(no attachment in message) X-Amp-File-Uploaded: False Received: from fmsmga003.fm.intel.com ([10.253.24.29]) by fmsmga107.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 04 Aug 2020 00:07:23 -0700 IronPort-SDR: aK3gG8XPUzHf6xw1EIiDqUUENEDtcIUESKPPjTAf4Tw+S2cF+peTsyhA6Lp/wDtxwJtulr+G1v r5Y3py+3JUhQ== X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.75,433,1589266800"; d="scan'208";a="330510365" Received: from ahunter-desktop.fi.intel.com (HELO [10.237.72.73]) ([10.237.72.73]) by FMSMGA003.fm.intel.com with ESMTP; 04 Aug 2020 00:07:20 -0700 Subject: Re: [PATCH v2] perf evsel: Don't set sample_regs_intr/sample_regs_user for dummy event To: "Jin, Yao" , Jiri Olsa Cc: acme@kernel.org, jolsa@kernel.org, peterz@infradead.org, mingo@redhat.com, alexander.shishkin@linux.intel.com, Linux-kernel@vger.kernel.org, ak@linux.intel.com, kan.liang@intel.com, yao.jin@intel.com, irogers@google.com References: <20200720010013.18238-1-yao.jin@linux.intel.com> <20200720091748.GH760733@krava> <20200722110810.GD981884@krava> <6f732f7f-7c5a-726f-5b09-2c6761f3b534@linux.intel.com> From: Adrian Hunter Organization: Intel Finland Oy, Registered Address: PL 281, 00181 Helsinki, Business Identity Code: 0357606 - 4, Domiciled in Helsinki Message-ID: <32664190-9a2b-6ce6-3cbc-87b46c85d21e@intel.com> Date: Tue, 4 Aug 2020 10:06:56 +0300 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.10.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 29/07/20 10:23 am, Jin, Yao wrote: > Hi Adrian, > > Could you help to check if following condition will break PT? > > "(opts->sample_intr_regs && !evsel->no_aux_samples && > !evsel__is_dummy_event(evsel))" Sorry for slow response - I've been away. This is fine. It will not break PT. no_aux_samples is useful for evsels that have been added by the code rather than requested by the user. For old kernels PT adds sched_switch tracepoint to track context switches (before the current context switch event was added) and having auxiliary sample information unnecessarily uses up space in the perf buffer. Acked-by: Adrian Hunter > > Thanks > Jin Yao > > On 7/23/2020 9:01 AM, Jin, Yao wrote: >> Hi Jiri, Adrian, >> >> On 7/22/2020 7:08 PM, Jiri Olsa wrote: >>> On Wed, Jul 22, 2020 at 01:00:03PM +0800, Jin, Yao wrote: >>> >>> SNIP >>> >>>>>> >>>>>> If we use -IXMM0, the attr>sample_regs_intr will be set with >>>>>> PERF_REG_EXTENDED_MASK bit. >>>>>> >>>>>> It doesn't make sense to set attr->sample_regs_intr for a >>>>>> software dummy event. >>>>>> >>>>>> This patch adds dummy event checking before setting >>>>>> attr->sample_regs_intr and attr->sample_regs_user. >>>>>> >>>>>> After: >>>>>>     # ./perf record -e cycles:p -IXMM0 -a -- sleep 1 >>>>>>     [ perf record: Woken up 1 times to write data ] >>>>>>     [ perf record: Captured and wrote 0.413 MB perf.data (45 samples) ] >>>>>> >>>>>>    v2: >>>>>>    --- >>>>>>    Rebase to perf/core >>>>>> >>>>>> Fixes: 0a892c1c9472 ("perf record: Add dummy event during system wide >>>>>> synthesis") >>>>>> Signed-off-by: Jin Yao >>>>>> --- >>>>>>    tools/perf/util/evsel.c | 6 ++++-- >>>>>>    1 file changed, 4 insertions(+), 2 deletions(-) >>>>>> >>>>>> diff --git a/tools/perf/util/evsel.c b/tools/perf/util/evsel.c >>>>>> index 9aa51a65593d..11794d3b7879 100644 >>>>>> --- a/tools/perf/util/evsel.c >>>>>> +++ b/tools/perf/util/evsel.c >>>>>> @@ -1014,12 +1014,14 @@ void evsel__config(struct evsel *evsel, struct >>>>>> record_opts *opts, >>>>>>        if (callchain && callchain->enabled && !evsel->no_aux_samples) >>>>>>            evsel__config_callchain(evsel, opts, callchain); >>>>>> -    if (opts->sample_intr_regs && !evsel->no_aux_samples) { >>>>>> +    if (opts->sample_intr_regs && !evsel->no_aux_samples && >>>>>> +        !evsel__is_dummy_event(evsel)) { >>>>> >>>>> hum, I thought it'd look something like this: >>>>> >>>>>     if (opts->sample_intr_regs && (!evsel->no_aux_samples || >>>>> !evsel__is_dummy_event(evsel)) >>>>> >>>>> but I'm not sure how no_aux_samples flag works exactly.. so it might be >>>>> correct.. just making sure ;-) >>>>> >>>>> cc-ing Adrian >>>>> >>>>> jirka >>>>> >>>>> >>>> >>>> no_aux_samples is set to false by default and it's only set to true by >>>> pt, right? >>>> >>>> So most of the time, !evsel->no_aux_samples is always true. >>>> >>>> if (opts->sample_intr_regs && (!evsel->no_aux_samples || >>>> !evsel__is_dummy_event(evsel)) { >>>>     attr->sample_regs_intr = opts->sample_intr_regs; >>>>     evsel__set_sample_bit(evsel, REGS_INTR); >>>> } >>>> >>>> So even if the evsel is dummy event, the condition check is true. :( >>>> >>>> Or maybe I misunderstand anything? >>> >>> I was just curious, because I did not follow the no_aux_samples >>> usage in detail.. so how about a case where: >>> >>>     evsel->no_aux_samples == true and evsel__is_dummy_event(evsel) = false >>> >>> then the original condition will be false for non dummy event >>> >>>    (opts->sample_intr_regs && !evsel->no_aux_samples && >>> !evsel__is_dummy_event(evsel)) >>> >>> is that ok? >>> >> >> I searched the perf source and found the no_aux_samples was only set to >> true in intel-pt.c. So I assume for the non-pt usage, the no_aux_samples >> is always false. >> >> For non-pt usage, >> (opts->sample_intr_regs && !evsel->no_aux_samples && >> !evsel__is_dummy_event(evsel)) is equal to >> (opts->sample_intr_regs && !evsel__is_dummy_event(evsel)) >> >> For pt usage, we need to consider the case that >> evsel__is_dummy_event(evsel) is true or false. >> >> If evsel__is_dummy_event(evsel) is true: >> (opts->sample_intr_regs && !evsel->no_aux_samples && >> !evsel__is_dummy_event(evsel)) is false. >> It's expected. >> >> If evsel__is_dummy_event(evsel) is false: >> (opts->sample_intr_regs && !evsel->no_aux_samples && >> !evsel__is_dummy_event(evsel)) is equal to >> (opts->sample_intr_regs && !evsel->no_aux_samples) >> That's the current code logic. >> >> So I think the condition "(opts->sample_intr_regs && >> !evsel->no_aux_samples && !evsel__is_dummy_event(evsel))" looks reasonable. >> >> Adrian, please correct me if I'm wrong here. >> >> Thanks >> Jin Yao >> >>> jirka >>>