From mboxrd@z Thu Jan 1 00:00:00 1970 From: Jiri Olsa Subject: Re: measuring system wide CPU usage ignoring idle process Date: Mon, 20 Nov 2017 15:29:08 +0100 Message-ID: <20171120142908.GA22876@krava> References: <3344812.IFj9h2T05j@agathebauer> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Received: from mx1.redhat.com ([209.132.183.28]:46229 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751124AbdKTO3J (ORCPT ); Mon, 20 Nov 2017 09:29:09 -0500 Content-Disposition: inline In-Reply-To: <3344812.IFj9h2T05j@agathebauer> Sender: linux-perf-users-owner@vger.kernel.org List-ID: To: Milian Wolff Cc: linux-perf-users@vger.kernel.org, acme@kernel.org, namhyung@kernel.org On Mon, Nov 20, 2017 at 03:00:46PM +0100, Milian Wolff wrote: > Hey all, > > colleagues of mine just brought this inconvenient perf stat behavior to my > attention: > > $ perf stat -a -e cpu-clock,task-clock,cycles,instructions sleep 1 > > Performance counter stats for 'system wide': > > 4004.501439 cpu-clock (msec) # 4.000 CPUs utilized > 4004.526474 task-clock (msec) # 4.000 CPUs utilized > 945,906,029 cycles # 0.236 GHz > 461,861,241 instructions # 0.49 insn per cycle > > 1.001247082 seconds time elapsed > > This shows that cpu-clock and task-clock are incremented also for the idle > processes. Is there some trick to exclude that time, such that the CPU > utilization drops below 100% when doing `perf stat -a`? I dont think it's the idle process you see, I think it's the managing overhead before the 'sleep 1' task goes actualy to sleep there's some user space code before it gets into the sleep syscall, and there's some possible kernel scheduling/syscall/irq code with events already enabled and counting in following 3 sessions you can see the counts are pretty much the same regardless the sleeping time: [jolsa@krava perf]$ sudo ./perf stat -e cycles:u,cycles:k sleep 1 Performance counter stats for 'sleep 1': 316,478 cycles:u 594,468 cycles:k 1.000813330 seconds time elapsed [jolsa@krava perf]$ sudo ./perf stat -e cycles:u,cycles:k sleep 5 Performance counter stats for 'sleep 5': 339,287 cycles:u 665,888 cycles:k 5.001004575 seconds time elapsed [jolsa@krava perf]$ sudo ./perf stat -e cycles:u,cycles:k sleep 10 Performance counter stats for 'sleep 10': 314,507 cycles:u 658,764 cycles:k 10.001117596 seconds time elapsed jirka