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=-2.5 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_PASS,URIBL_BLOCKED,USER_AGENT_MUTT 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 947D3C43381 for ; Fri, 15 Mar 2019 16:17:12 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 6BD9921871 for ; Fri, 15 Mar 2019 16:17:12 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729488AbfCOQRL (ORCPT ); Fri, 15 Mar 2019 12:17:11 -0400 Received: from mx1.redhat.com ([209.132.183.28]:47364 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726632AbfCOQRK (ORCPT ); Fri, 15 Mar 2019 12:17:10 -0400 Received: from smtp.corp.redhat.com (int-mx06.intmail.prod.int.phx2.redhat.com [10.5.11.16]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id 5666F68575; Fri, 15 Mar 2019 16:17:10 +0000 (UTC) Received: from pauld.bos.csb (dhcp-17-51.bos.redhat.com [10.18.17.51]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 830D25C219; Fri, 15 Mar 2019 16:17:09 +0000 (UTC) Date: Fri, 15 Mar 2019 12:17:07 -0400 From: Phil Auld To: Peter Zijlstra Cc: linux-kernel@vger.kernel.org, Ben Segall , Ingo Molnar Subject: Re: [PATCH] sched/fair: Limit sched_cfs_period_timer loop to avoid hard lockup Message-ID: <20190315161707.GG27131@pauld.bos.csb> References: <20190313150826.16862-1-pauld@redhat.com> <20190315101150.GV5996@hirez.programming.kicks-ass.net> <20190315153042.GF27131@pauld.bos.csb> <20190315160347.GZ5996@hirez.programming.kicks-ass.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190315160347.GZ5996@hirez.programming.kicks-ass.net> User-Agent: Mutt/1.5.21 (2010-09-15) X-Scanned-By: MIMEDefang 2.79 on 10.5.11.16 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.28]); Fri, 15 Mar 2019 16:17:10 +0000 (UTC) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Mar 15, 2019 at 05:03:47PM +0100 Peter Zijlstra wrote: > On Fri, Mar 15, 2019 at 11:30:42AM -0400, Phil Auld wrote: > > > In my defense here, all the fair.c imbalance pct code also uses 100 :) > > Yes, I know, I hate on that too ;-) Just never got around to fixing > that. > > > > with the below: > > > > [ 117.235804] cfs_period_timer[cpu2]: period too short, scaling up (new cfs_period_us 2492, cfs_quota_us = 143554) > > [ 117.346807] cfs_period_timer[cpu2]: period too short, scaling up (new cfs_period_us 2862, cfs_quota_us = 164863) > > [ 117.470569] cfs_period_timer[cpu2]: period too short, scaling up (new cfs_period_us 3286, cfs_quota_us = 189335) > > [ 117.574883] cfs_period_timer[cpu2]: period too short, scaling up (new cfs_period_us 3774, cfs_quota_us = 217439) > > [ 117.652907] cfs_period_timer[cpu2]: period too short, scaling up (new cfs_period_us 4335, cfs_quota_us = 249716) > > [ 118.090535] cfs_period_timer[cpu2]: period too short, scaling up (new cfs_period_us 4978, cfs_quota_us = 286783) > > [ 122.098009] cfs_period_timer[cpu2]: period too short, scaling up (new cfs_period_us 5717, cfs_quota_us = 329352) > > [ 126.255209] cfs_period_timer[cpu2]: period too short, scaling up (new cfs_period_us 6566, cfs_quota_us = 378240) > > [ 126.358060] cfs_period_timer[cpu2]: period too short, scaling up (new cfs_period_us 7540, cfs_quota_us = 434385) > > [ 126.538358] cfs_period_timer[cpu9]: period too short, scaling up (new cfs_period_us 8660, cfs_quota_us = 498865) > > [ 126.614304] cfs_period_timer[cpu9]: period too short, scaling up (new cfs_period_us 9945, cfs_quota_us = 572915) > > [ 126.817085] cfs_period_timer[cpu9]: period too short, scaling up (new cfs_period_us 11422, cfs_quota_us = 657957) > > [ 127.352038] cfs_period_timer[cpu9]: period too short, scaling up (new cfs_period_us 13117, cfs_quota_us = 755623) > > [ 127.598043] cfs_period_timer[cpu9]: period too short, scaling up (new cfs_period_us 15064, cfs_quota_us = 867785) > > > > > > Plus on repeats I see an occasional > > > > [ 152.803384] sched_cfs_period_timer: 9 callbacks suppressed > > That should be fine, right? It's a fallback for an edge case and > shouldn't trigger too often anyway. It doesn't hit the NMI, just takes a bit longer to get out. It is a little messier output, but as you say, it's a fallback. If you're okay with it do you want to just use your patch? Otherwise, I'm happy to do a fixup v2. > > >> I'll rework the maths in the averaged version and post v2 if that makes sense. > > > > It may have the extra timer fetch, although maybe I could rework it so that it used the > > nsstart time the first time and did not need to do it twice in a row. I had originally > > reverted the hrtimer_forward_now() to hrtimer_forward() but put that back. > > Sure; but remember, simpler is often better, esp. for code that > typically 'never' runs. > > > Also, fwiw, this was reported earlier by Anton Blanchard in https://lkml.org/lkml/2018/12/3/1047 > > Bah, yes, I sometimes loose track of things :/ No worries. I just meant that to show I was not the only one with these low settings, and to give credit, or whatever :) Cheers, Phil --