From patchwork Tue Jul 17 06:50:48 2018 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Andreas Herrmann X-Patchwork-Id: 10528175 Return-Path: Received: from mail.wl.linuxfoundation.org (pdx-wl-mail.web.codeaurora.org [172.30.200.125]) by pdx-korg-patchwork.web.codeaurora.org (Postfix) with ESMTP id C2354601D2 for ; Tue, 17 Jul 2018 06:50:58 +0000 (UTC) Received: from mail.wl.linuxfoundation.org (localhost [127.0.0.1]) by mail.wl.linuxfoundation.org (Postfix) with ESMTP id BAC8028BD0 for ; Tue, 17 Jul 2018 06:50:58 +0000 (UTC) Received: by mail.wl.linuxfoundation.org (Postfix, from userid 486) id B85FF28BDD; Tue, 17 Jul 2018 06:50:58 +0000 (UTC) X-Spam-Checker-Version: SpamAssassin 3.3.1 (2010-03-16) on pdx-wl-mail.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-7.9 required=2.0 tests=BAYES_00, MAILING_LIST_MULTI, RCVD_IN_DNSWL_HI autolearn=ham version=3.3.1 Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.wl.linuxfoundation.org (Postfix) with ESMTP id 3764028B81 for ; Tue, 17 Jul 2018 06:50:58 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727961AbeGQHWA (ORCPT ); Tue, 17 Jul 2018 03:22:00 -0400 Received: from smtp.nue.novell.com ([195.135.221.5]:56308 "EHLO smtp.nue.novell.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727796AbeGQHWA (ORCPT ); Tue, 17 Jul 2018 03:22:00 -0400 Received: from emea4-mta.ukb.novell.com ([10.120.13.87]) by smtp.nue.novell.com with ESMTP (TLS encrypted); Tue, 17 Jul 2018 08:50:55 +0200 Received: from suselix (nwb-a10-snat.microfocus.com [10.120.13.201]) by emea4-mta.ukb.novell.com with ESMTP (TLS encrypted); Tue, 17 Jul 2018 07:50:49 +0100 Date: Tue, 17 Jul 2018 08:50:48 +0200 From: Andreas Herrmann To: "Rafael J. Wysocki" Cc: Peter Zijlstra , Frederic Weisbecker , Viresh Kumar , linux-pm@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Commit 554c8aa8ecad causing severe performance degression with pcc-cpufreq Message-ID: <20180717065048.74mmgk4t5utjaa6a@suselix> MIME-Version: 1.0 Content-Disposition: inline User-Agent: NeoMutt/20170421 (1.8.2) Sender: linux-pm-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-pm@vger.kernel.org X-Virus-Scanned: ClamAV using ClamSMTP Hello, I've recently noticed that commit 554c8aa8ecad ("sched: idle: Select idle state before stopping the tick") causes severe performance drop for systems using pcc-cpufreq driver. Depending on the number of CPUs the system might be almost unusable. The OS jitter for 4.17.y and 4.18.-rcx kernels is off the charts, you can even spot it with top command (issued when the system is supposedly idle), e.g. top - 14:44:24 up 2 min, 1 user, load average: 90.11, 38.20, 14.38 Tasks: 1199 total, 109 running, 541 sleeping, 0 stopped, 0 zombie %Cpu(s): 1.2 us, 58.7 sy, 0.0 ni, 39.3 id, 0.6 wa, 0.0 hi, 0.3 si, 0.0 st KiB Mem: 13137064+total, 1192168 used, 13017848+free, 2340 buffers KiB Swap: 2104316 total, 0 used, 2104316 free. 522296 cached Mem PID USER PR NI VIRT RES SHR S %CPU %MEM TIME+ COMMAND 3373 root 20 0 982024 49916 36120 R 96.691 0.038 0:19.54 kubelet 67 root 20 0 0 0 0 R 78.676 0.000 0:49.36 kworker/9:0 25 root 20 0 0 0 0 R 78.125 0.000 0:49.67 kworker/2:0 182 root 20 0 0 0 0 R 75.735 0.000 1:18.17 kworker/28:0 43 root 20 0 0 0 0 R 75.000 0.000 0:11.56 kworker/5:0 103 root 20 0 0 0 0 R 74.449 0.000 0:46.83 kworker/15:0 334 root 20 0 0 0 0 R 72.978 0.000 1:06.88 kworker/53:0 789 root 20 0 0 0 0 R 69.853 0.000 1:29.50 kworker/38:1 418 root 20 0 0 0 0 R 69.301 0.000 0:41.33 kworker/67:0 779 root 20 0 0 0 0 R 68.934 0.000 1:33.60 kworker/27:1 773 root 20 0 0 0 0 R 68.566 0.000 1:37.91 kworker/22:1 762 root 20 0 0 0 0 R 68.015 0.000 1:41.01 kworker/11:1 769 root 20 0 0 0 0 R 67.647 0.000 1:37.65 kworker/18:1 805 root 20 0 0 0 0 R 67.096 0.000 1:30.96 kworker/54:1 840 root 20 0 0 0 0 R 66.912 0.000 1:23.82 kworker/89:1 812 root 20 0 0 0 0 R 66.728 0.000 1:31.89 kworker/59:1 847 root 20 0 0 0 0 R 66.360 0.000 1:28.40 kworker/96:1 763 root 20 0 0 0 0 R 66.176 0.000 1:42.57 kworker/12:1 772 root 20 0 0 0 0 R 66.176 0.000 1:12.58 kworker/21:1 821 root 20 0 0 0 0 R 66.176 0.000 1:29.62 kworker/69:1 923 root 20 0 0 0 0 R 65.809 0.000 1:44.32 kworker/3:18 1284 root 20 0 0 0 0 R 65.809 0.000 1:23.50 kworker/101:2 61 root 20 0 0 0 0 R 65.625 0.000 1:29.37 kworker/8:0 3531 root 20 0 24384 3768 2356 R 65.625 0.003 0:08.91 top 771 root 20 0 0 0 0 R 65.074 0.000 1:37.90 kworker/20:1 767 root 20 0 0 0 0 R 64.706 0.000 1:38.01 kworker/16:1 764 root 20 0 0 0 0 R 64.522 0.000 1:40.28 kworker/13:1 765 root 20 0 0 0 0 R 64.154 0.000 1:40.13 kworker/14:1 When I apply below patch (trying to revert essential parts of commit 554c8aa8ecad) behaviour seems back to normal. I know that pcc-cpufreq driver is not "state-of-the-art" when it comes to cpufreq drivers and you better not use it. But I wonder whether commit 554c8aa8ecad ("sched: idle: Select idle state before stopping the tick") introduced bad behaviour for other cases as well. I'll send some performance results to illustrate the issue asap. I've also tried to modify pcc-cpufreq to reduce the amount of frequency changes triggered by this driver but this does not help for kernels where commit 554c8aa8ecad is applied. Andreas diff --git a/kernel/sched/idle.c b/kernel/sched/idle.c index 1a3e9bddd17b..377a62ec475c 100644 --- a/kernel/sched/idle.c +++ b/kernel/sched/idle.c @@ -185,18 +185,13 @@ static void cpuidle_idle_call(void) } else { bool stop_tick = true; + tick_nohz_idle_stop_tick(); + rcu_idle_enter(); /* * Ask the cpuidle framework to choose a convenient idle state. */ next_state = cpuidle_select(drv, dev, &stop_tick); - if (stop_tick) - tick_nohz_idle_stop_tick(); - else - tick_nohz_idle_retain_tick(); - - rcu_idle_enter(); - entered_state = call_cpuidle(drv, dev, next_state); /* * Give the governor an opportunity to reflect on the outcome