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_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 autolearn=no 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 30B9EC433E0 for ; Fri, 3 Jul 2020 20:52:01 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 050C520885 for ; Fri, 3 Jul 2020 20:52:01 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726925AbgGCUv7 (ORCPT ); Fri, 3 Jul 2020 16:51:59 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:45394 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726752AbgGCUv7 (ORCPT ); Fri, 3 Jul 2020 16:51:59 -0400 Received: from scorn.kernelslacker.org (scorn.kernelslacker.org [IPv6:2600:3c03:e000:2fb::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 2CA93C061794 for ; Fri, 3 Jul 2020 13:51:59 -0700 (PDT) Received: from [2601:196:4600:6634:ae9e:17ff:feb7:72ca] (helo=wopr.kernelslacker.org) by scorn.kernelslacker.org with esmtp (Exim 4.92) (envelope-from ) id 1jrSf4-00057k-B1; Fri, 03 Jul 2020 16:51:54 -0400 Received: by wopr.kernelslacker.org (Postfix, from userid 1026) id F3887560110; Fri, 3 Jul 2020 16:51:53 -0400 (EDT) Date: Fri, 3 Jul 2020 16:51:53 -0400 From: Dave Jones To: Peter Zijlstra Cc: Mel Gorman , Linux Kernel , mingo@kernel.org, Linus Torvalds Subject: Re: weird loadavg on idle machine post 5.7 Message-ID: <20200703205153.GA19901@codemonkey.org.uk> Mail-Followup-To: Dave Jones , Peter Zijlstra , Mel Gorman , Linux Kernel , mingo@kernel.org, Linus Torvalds References: <20200702171548.GA11813@codemonkey.org.uk> <20200702213627.GF3183@techsingularity.net> <20200703090226.GV4800@hirez.programming.kicks-ass.net> <20200703104033.GK117543@hirez.programming.kicks-ass.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200703104033.GK117543@hirez.programming.kicks-ass.net> User-Agent: Mutt/1.10.1 (2018-07-13) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Jul 03, 2020 at 12:40:33PM +0200, Peter Zijlstra wrote: > So ARM/Power/etc.. can speculate the load such that the > task_contributes_to_load() value is from before ->on_rq. > > The compiler might similar re-order things -- although I've not found it > doing so with the few builds I looked at. > > So I think at the very least we should do something like this. But i've > no idea how to reproduce this problem. > > Mel's patch placed it too far down, as the WF_ON_CPU path also relies on > this, and by not resetting p->sched_contributes_to_load it would skew > accounting even worse. looked promising the first few hours, but as soon as it hit four hours of uptime, loadavg spiked and is now pinned to at least 1.00 Dave