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=-3.9 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,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 B1F1BC388F7 for ; Thu, 22 Oct 2020 15:12:20 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 5041524630 for ; Thu, 22 Oct 2020 15:12:20 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="QacrUXZG" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S368498AbgJVPMT (ORCPT ); Thu, 22 Oct 2020 11:12:19 -0400 Received: from us-smtp-delivery-124.mimecast.com ([63.128.21.124]:36292 "EHLO us-smtp-delivery-124.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S368432AbgJVPMR (ORCPT ); Thu, 22 Oct 2020 11:12:17 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1603379536; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=uDlJvVtWMlPWw+lQx90tQ7kEfUNHvkpfYYWbomFbvhA=; b=QacrUXZGTFkmWMLriwhtv9Xp3reNIXmA+Mip6T76HeNKWBRbZfG+SGSKdSp6nrNda1wAkk O3XDu4ag9sqoxBgaXo1dtn70S20a5IvDLdGfJDEDit+Yk88ODhMbcWkDz5btxz0dOU0EYN /D2eyG0Hf158yRdDwRGW2Y4IsV7awHM= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-584-nYS15yLeNbO5z0Blf0cGTA-1; Thu, 22 Oct 2020 11:12:13 -0400 X-MC-Unique: nYS15yLeNbO5z0Blf0cGTA-1 Received: from smtp.corp.redhat.com (int-mx05.intmail.prod.int.phx2.redhat.com [10.5.11.15]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 108C41882FA1; Thu, 22 Oct 2020 15:12:11 +0000 (UTC) Received: from lorien.usersys.redhat.com (ovpn-113-70.phx2.redhat.com [10.3.113.70]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 4253C55776; Thu, 22 Oct 2020 15:12:02 +0000 (UTC) Date: Thu, 22 Oct 2020 11:12:00 -0400 From: Phil Auld To: Colin Ian King Cc: Mel Gorman , Peter Zijlstra , "Rafael J. Wysocki" , Giovanni Gherdovich , Viresh Kumar , Julia Lawall , Ingo Molnar , kernel-janitors@vger.kernel.org, Juri Lelli , Vincent Guittot , Dietmar Eggemann , Steven Rostedt , Ben Segall , Daniel Bristot de Oliveira , linux-kernel@vger.kernel.org, Valentin Schneider , Gilles Muller , srinivas.pandruvada@linux.intel.com, Linux PM , Len Brown Subject: Re: default cpufreq gov, was: [PATCH] sched/fair: check for idle core Message-ID: <20201022151200.GC92942@lorien.usersys.redhat.com> References: <1603211879-1064-1-git-send-email-Julia.Lawall@inria.fr> <34115486.YmRjPRKJaA@kreacher> <20201022120213.GG2611@hirez.programming.kicks-ass.net> <1790766.jaFeG3T87Z@kreacher> <20201022122949.GW2628@hirez.programming.kicks-ass.net> <20201022145250.GK32041@suse.de> <6606e5f4-3f66-5844-da02-5b11e1464be6@canonical.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <6606e5f4-3f66-5844-da02-5b11e1464be6@canonical.com> X-Scanned-By: MIMEDefang 2.79 on 10.5.11.15 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Oct 22, 2020 at 03:58:13PM +0100 Colin Ian King wrote: > On 22/10/2020 15:52, Mel Gorman wrote: > > On Thu, Oct 22, 2020 at 02:29:49PM +0200, Peter Zijlstra wrote: > >> On Thu, Oct 22, 2020 at 02:19:29PM +0200, Rafael J. Wysocki wrote: > >>>> However I do want to retire ondemand, conservative and also very much > >>>> intel_pstate/active mode. > >>> > >>> I agree in general, but IMO it would not be prudent to do that without making > >>> schedutil provide the same level of performance in all of the relevant use > >>> cases. > >> > >> Agreed; I though to have understood we were there already. > > > > AFAIK, not quite (added Giovanni as he has been paying more attention). > > Schedutil has improved since it was merged but not to the extent where > > it is a drop-in replacement. The standard it needs to meet is that > > it is at least equivalent to powersave (in intel_pstate language) > > or ondemand (acpi_cpufreq) and within a reasonable percentage of the > > performance governor. Defaulting to performance is a) giving up and b) > > the performance governor is not a universal win. There are some questions > > currently on whether schedutil is good enough when HWP is not available. > > There was some evidence (I don't have the data, Giovanni was looking into > > it) that HWP was a requirement to make schedutil work well. That is a > > hazard in itself because someone could test on the latest gen Intel CPU > > and conclude everything is fine and miss that Intel-specific technology > > is needed to make it work well while throwing everyone else under a bus. > > Giovanni knows a lot more than I do about this, I could be wrong or > > forgetting things. > > > > For distros, switching to schedutil by default would be nice because > > frequency selection state would follow the task instead of being per-cpu > > and we could stop worrying about different HWP implementations but it's > > not at the point where the switch is advisable. I would expect hard data > > before switching the default and still would strongly advise having a > > period of time where we can fall back when someone inevitably finds a > > new corner case or exception. > > ..and it would be really useful for distros to know when the hard data > is available so that they can make an informed decision when to move to > schedutil. > I think distros are on the hook to generate that hard data themselves with which to make such a decision. I don't expect it to be done by someone else. > > > > For reference, SLUB had the same problem for years. It was switched > > on by default in the kernel config but it was a long time before > > SLUB was generally equivalent to SLAB in terms of performance. Block > > multiqueue also had vaguely similar issues before the default changes > > and a period of time before it was removed removed (example whinging mail > > https://lore.kernel.org/lkml/20170803085115.r2jfz2lofy5spfdb@techsingularity.net/) > > It's schedutil's turn :P > > > Agreed. I'd like the option to switch back if we make the default change. It's on the table and I'd like to be able to go that way. Cheers, Phil --