From mboxrd@z Thu Jan 1 00:00:00 1970 From: Viresh Kumar Subject: Re: [PATCH] cpufreq: schedutil: add up/down frequency transition rate limits Date: Mon, 21 Nov 2016 17:00:16 +0530 Message-ID: <20161121113016.GD10014@vireshk-i7> References: <20161121100805.GB10014@vireshk-i7> <20161121101946.GI3102@twins.programming.kicks-ass.net> <20161121104800.GC10014@vireshk-i7> <20161121111243.GK3102@twins.programming.kicks-ass.net> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Received: from mail-pf0-f180.google.com ([209.85.192.180]:33032 "EHLO mail-pf0-f180.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754175AbcKULaV (ORCPT ); Mon, 21 Nov 2016 06:30:21 -0500 Received: by mail-pf0-f180.google.com with SMTP id d2so64358670pfd.0 for ; Mon, 21 Nov 2016 03:30:20 -0800 (PST) Content-Disposition: inline In-Reply-To: <20161121111243.GK3102@twins.programming.kicks-ass.net> Sender: linux-pm-owner@vger.kernel.org List-Id: linux-pm@vger.kernel.org To: Peter Zijlstra Cc: Rafael Wysocki , Ingo Molnar , linaro-kernel@lists.linaro.org, linux-pm@vger.kernel.org, linux-kernel@vger.kernel.org, Vincent Guittot , Juri Lelli , Robin Randhawa , Steve Muckle , tkjos@google.com, Morten Rasmussen On 21-11-16, 12:12, Peter Zijlstra wrote: > I think it should be replaced by a value provided by the driver. It > makes sense to have a rate-limit in so far as that it doesn't make sense > to try and program the hardware faster than it can actually change > frequencies and/or have a programming cost amortization. And this very > clearly is a driver specific thing. We already have something called as transition_latency for that (though it isn't used much currently). > It however doesn't make sense to me to fudge with this in order to > achieve ramp up/down differences. So if a platform, for example, can do DVFS in say 100-500 us, then the scheduler should try to re-evaluate frequency (and update it) after that short of a period? Wouldn't that scheme waste lots of time doing just freq updates? And that's the primary reason why cpufreq governors have some sort of sampling-rate or rate-limit until now. -- viresh