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=-0.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS 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 77A36C33CB1 for ; Wed, 15 Jan 2020 15:10:01 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 5384B2187F for ; Wed, 15 Jan 2020 15:10:01 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729182AbgAOPKA convert rfc822-to-8bit (ORCPT ); Wed, 15 Jan 2020 10:10:00 -0500 Received: from eu-smtp-delivery-151.mimecast.com ([207.82.80.151]:31841 "EHLO eu-smtp-delivery-151.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726418AbgAOPKA (ORCPT ); Wed, 15 Jan 2020 10:10:00 -0500 Received: from AcuMS.aculab.com (156.67.243.126 [156.67.243.126]) (Using TLS) by relay.mimecast.com with ESMTP id uk-mta-68-0IKbv8msNxKpwXV72oqKfw-1; Wed, 15 Jan 2020 15:09:57 +0000 Received: from AcuMS.Aculab.com (fd9f:af1c:a25b:0:43c:695e:880f:8750) by AcuMS.aculab.com (fd9f:af1c:a25b:0:43c:695e:880f:8750) with Microsoft SMTP Server (TLS) id 15.0.1347.2; Wed, 15 Jan 2020 15:09:56 +0000 Received: from AcuMS.Aculab.com ([fe80::43c:695e:880f:8750]) by AcuMS.aculab.com ([fe80::43c:695e:880f:8750%12]) with mapi id 15.00.1347.000; Wed, 15 Jan 2020 15:09:56 +0000 From: David Laight To: 'Peter Zijlstra' CC: 'Steven Rostedt' , 'Vincent Guittot' , Viresh Kumar , "Ingo Molnar" , Juri Lelli , "Dietmar Eggemann" , Ben Segall , "Mel Gorman" , linux-kernel Subject: RE: sched/fair: scheduler not running high priority process on idle cpu Thread-Topic: sched/fair: scheduler not running high priority process on idle cpu Thread-Index: AdXK8cUFXa7JpPXmQNq7oQ32S9fYHAACik4AAADJLkAAAO3PAAAmXEggAAXxcIAAADWFcA== Date: Wed, 15 Jan 2020 15:09:56 +0000 Message-ID: References: <212fabd759b0486aa8df588477acf6d0@AcuMS.aculab.com> <20200114115906.22f952ff@gandalf.local.home> <5ba2ae2d426c4058b314c20c25a9b1d0@AcuMS.aculab.com> <20200114124812.4d5355ae@gandalf.local.home> <878a35a6642d482aa0770a055506bd5e@AcuMS.aculab.com> <20200115145645.GM2827@hirez.programming.kicks-ass.net> In-Reply-To: <20200115145645.GM2827@hirez.programming.kicks-ass.net> Accept-Language: en-GB, en-US Content-Language: en-US X-MS-Has-Attach: X-MS-TNEF-Correlator: x-ms-exchange-transport-fromentityheader: Hosted x-originating-ip: [10.202.205.107] MIME-Version: 1.0 X-MC-Unique: 0IKbv8msNxKpwXV72oqKfw-1 X-Mimecast-Spam-Score: 0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8BIT Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Peter Zijlstra > Sent: 15 January 2020 14:57 > On Wed, Jan 15, 2020 at 12:44:19PM +0000, David Laight wrote: > > > Code that runs with a spin-lock held (or otherwise disables preemption) > > for significant periods probably ought to be detected and warned. > > I'm not sure of a suitable limit, 100us is probably excessive on x86. > > Problem is, without CONFIG_PREEMPT_COUNT (basically only > PREEMPT/PREEMPT_RT) we can't even tell. > > And I think we tried adding warnings to things like softirq, but then we > get into arguments with the pure performance people on how allowing it > longer will make their benchmarks go faster. The interval would have to be a sysctl - like the one for sleeping uninterruptibly. (Although that one is a pain for some kernel threads. I'd like to be able to mark some uninterruptible sleeps as 'long term' and also not affecting the load average.) I remember (a long time ago) adding code to an ethernet driver to limit it to 90% of the bandwidth to allow other systems to transmit (10M HDX). Someone said ' we can't do that, people expect 100%', a week later he asked me how to enable it because the AMD Lance could never transmit if receiving back to back packets (eg in promiscuous mode). Benchmarks are a PITA.... David - Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK Registration No: 1397386 (Wales)