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=-7.0 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_PASS,URIBL_BLOCKED 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 31962C43387 for ; Sat, 5 Jan 2019 03:16:45 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id F20802173B for ; Sat, 5 Jan 2019 03:16:44 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726116AbfAEDQo (ORCPT ); Fri, 4 Jan 2019 22:16:44 -0500 Received: from mga05.intel.com ([192.55.52.43]:35167 "EHLO mga05.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726010AbfAEDQn (ORCPT ); Fri, 4 Jan 2019 22:16:43 -0500 X-Amp-Result: SKIPPED(no attachment in message) X-Amp-File-Uploaded: False Received: from orsmga006.jf.intel.com ([10.7.209.51]) by fmsmga105.fm.intel.com with ESMTP/TLS/DHE-RSA-AES256-GCM-SHA384; 04 Jan 2019 19:16:43 -0800 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.56,441,1539673200"; d="scan'208";a="105643403" Received: from yjin15-mobl.ccr.corp.intel.com (HELO [10.254.215.18]) ([10.254.215.18]) by orsmga006.jf.intel.com with ESMTP; 04 Jan 2019 19:16:41 -0800 Subject: Re: [PATCH] perf stat: Poll for monitored tasks being alive in fork mode To: 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 References: <1546568897-16123-1-git-send-email-yao.jin@linux.intel.com> <20190104125441.GF5481@krava> From: "Jin, Yao" Message-ID: Date: Sat, 5 Jan 2019 11:16:40 +0800 User-Agent: Mozilla/5.0 (Windows NT 10.0; WOW64; rv:60.0) Gecko/20100101 Thunderbird/60.3.3 MIME-Version: 1.0 In-Reply-To: <20190104125441.GF5481@krava> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 1/4/2019 8:54 PM, Jiri Olsa wrote: > On Fri, Jan 04, 2019 at 10:28:17AM +0800, Jin Yao wrote: >> Following test shows the stat keeps running even if no longer >> task to monitor (mgen exits at ~5s). >> >> perf stat -e cycles -p `pgrep mgen` -I1000 -- sleep 10 >> time counts unit events >> 1.000148916 1,308,365,864 cycles >> 2.000379171 1,297,269,875 cycles >> 3.000556719 1,297,187,078 cycles >> 4.000914241 761,261,827 cycles >> 5.001306091 cycles >> 6.001676881 cycles >> 7.002046336 cycles >> 8.002405651 cycles >> 9.002766625 cycles >> 10.001395827 cycles >> >> We'd better finish stat immediately if there's no longer task to >> monitor. >> >> After: >> >> perf stat -e cycles -p `pgrep mgen` -I1000 -- sleep 10 >> time counts unit events >> 1.000180062 1,236,592,661 cycles >> 2.000421539 1,223,733,572 cycles >> 3.000609910 1,297,047,663 cycles >> 4.000807545 1,297,215,816 cycles >> 5.001001578 1,297,208,032 cycles >> 6.001390345 582,343,659 cycles >> sleep: Terminated >> >> Now the stat exits immediately when the monitored tasks ends. >> >> Signed-off-by: Jin Yao >> --- >> tools/perf/builtin-stat.c | 7 +++++++ >> 1 file changed, 7 insertions(+) >> >> diff --git a/tools/perf/builtin-stat.c b/tools/perf/builtin-stat.c >> index 63a3afc..71f3bc8 100644 >> --- a/tools/perf/builtin-stat.c >> +++ b/tools/perf/builtin-stat.c >> @@ -553,6 +553,13 @@ static int __run_perf_stat(int argc, const char **argv, int run_idx) >> >> if (interval || timeout) { >> while (!waitpid(child_pid, &status, WNOHANG)) { >> + if (!is_target_alive(&target, >> + evsel_list->threads) && >> + (child_pid != -1)) { > > do we need that child_pid check? we just returned from waitpid > so we should be ok.. we just make the race window smaller > > could we just do: > > if (!is_target_alive(&target, evsel_list->threads)) { > kill(child_pid, SIGTERM); > break; > } > I think this code should be OK and I have tested yet. I have a question about the race condition, we really don't need a lock to protect the child_pid? skip_signal() { /* * render child_pid harmless * won't send SIGTERM to a random * process in case of race condition * and fast PID recycling */ child_pid = -1; } __run_perf_stat() { .... kill(child_pid, SIGTERM); } If child_pid is set by -1 in a small window between checking of child_pid and kill(), then kill(-1, SIGTERM) may happen. All processes except the kill process itself and init would receive SIGTERM. Is this case possible? > also I'm not sure we should do this only under new option, > as it might break people's scripts.. thoughts? > > jirka > In current behavior, for non fork mode, if we terminate the monitored task, the perf stat would return immediately. So I think this patch should be OK. Thanks Jin Yao >> + kill(child_pid, SIGTERM); >> + break; >> + } >> + >> nanosleep(&ts, NULL); >> if (timeout) >> break; >> -- >> 2.7.4 >>