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=-2.3 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,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 7EFF4C32750 for ; Fri, 2 Aug 2019 14:09:00 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 5852620B7C for ; Fri, 2 Aug 2019 14:09:00 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2436609AbfHBOI7 (ORCPT ); Fri, 2 Aug 2019 10:08:59 -0400 Received: from foss.arm.com ([217.140.110.172]:52540 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1732817AbfHBOI6 (ORCPT ); Fri, 2 Aug 2019 10:08:58 -0400 Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id D66631570; Fri, 2 Aug 2019 07:08:57 -0700 (PDT) Received: from e107158-lin.cambridge.arm.com (unknown [10.1.194.52]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 15B183F575; Fri, 2 Aug 2019 07:08:56 -0700 (PDT) Date: Fri, 2 Aug 2019 15:08:54 +0100 From: Qais Yousef To: Peter Zijlstra Cc: mingo@kernel.org, linux-kernel@vger.kernel.org, Geert Uytterhoeven , Thomas Gleixner Subject: Re: [PATCH 0/5] Fix FIFO-99 abuse Message-ID: <20190802140854.ixq4cmo5nsfdaj24@e107158-lin.cambridge.arm.com> References: <20190801111348.530242235@infradead.org> <20190801131707.5rpyydznnhz474la@e107158-lin.cambridge.arm.com> <20190802093244.GF2332@hirez.programming.kicks-ass.net> <20190802102611.54sae3onftck5fye@e107158-lin.cambridge.arm.com> <20190802124151.GG2332@hirez.programming.kicks-ass.net> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <20190802124151.GG2332@hirez.programming.kicks-ass.net> User-Agent: NeoMutt/20171215 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 08/02/19 14:41, Peter Zijlstra wrote: > On Fri, Aug 02, 2019 at 11:26:12AM +0100, Qais Yousef wrote: > > > Yes a somewhat enforced default makes more sense to me. I assume you no longer > > want to put the kthreads that just need to be above OTHER in FIFO-1? > > I'm not sure, maybe, there's not that many of them, but possibly we add > another interface for them. By the way, did you see this one which is set to priority 16? https://elixir.bootlin.com/linux/v5.3-rc2/source/drivers/gpu/drm/msm/msm_drv.c#L523 > > > While at it, since we will cram all kthreads on the same priority, isn't > > a SCHED_RR a better choice now? I think the probability of a clash is pretty > > low, but when it happens, shouldn't we try to guarantee some fairness? > > It's never been a problem, and aside from these few straggler threads, > everybody has effectively been there already for years, so if it were a > problem someone would've complained by now. Usually they can run on enough CPUs so a real clash is definitely hard. I'm trying to collect data on that, if I find something interesting I'll share it. > > Also; like said before, the admin had better configure. I agree. But I don't think an 'admin' is an easily defined entity for all systems. On mobile, is it the SoC vendor, Android framework, or the handset/platform vendor/integrator? In a *real* realtime system I think things are better defined. But usage of RT tasks on generic systems is the confusing part. There's no real ownership and things are more ad-hoc. > > Also also, RR-SMP is actually broken (and nobody has cared enough to > bother fixing it). If you can give me enough pointers to understand the problem I might be able to bother with it :-) Thanks -- Qais Yousef