From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753464AbeAaLyJ (ORCPT ); Wed, 31 Jan 2018 06:54:09 -0500 Received: from outbound-smtp23.blacknight.com ([81.17.249.191]:53530 "EHLO outbound-smtp23.blacknight.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751587AbeAaLyI (ORCPT ); Wed, 31 Jan 2018 06:54:08 -0500 Date: Wed, 31 Jan 2018 11:54:06 +0000 From: Mel Gorman To: Peter Zijlstra Cc: "Rafael J. Wysocki" , Mike Galbraith , Matt Fleming , LKML , srinivas.pandruvada@linux.intel.com Subject: Re: [PATCH 4/4] sched/fair: Use a recently used CPU as an idle candidate and the basis for SIS Message-ID: <20180131115406.4g7oj46xhmteefc5@techsingularity.net> References: <20180130104555.4125-1-mgorman@techsingularity.net> <20180130125718.iwntjuvcp3yplvdx@techsingularity.net> <20180130131531.GD2269@hirez.programming.kicks-ass.net> <4353713.vEOq6OHvJN@aspire.rjw.lan> <20180131101710.GM2269@hirez.programming.kicks-ass.net> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-15 Content-Disposition: inline In-Reply-To: <20180131101710.GM2269@hirez.programming.kicks-ass.net> User-Agent: NeoMutt/20170912 (1.9.0) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Jan 31, 2018 at 11:17:10AM +0100, Peter Zijlstra wrote: > On Wed, Jan 31, 2018 at 10:22:49AM +0100, Rafael J. Wysocki wrote: > > On Tuesday, January 30, 2018 2:15:31 PM CET Peter Zijlstra wrote: > > > > IA32_HWP_REQUEST has "Minimum_Performance", "Maximum_Performance" and > > > "Desired_Performance" fields which can be used to give explicit > > > frequency hints. And we really _should_ be doing that. > > > > > > Because, esp. in this scenario; a task migrating; the hardware really > > > can't do anything sensible, whereas the OS _knows_. > > > > But IA32_HWP_REQUEST is not a cheap MSR to write to. > > That just means we might need to throttle writing to it, like it already > does for the regular pstate (PERF_CTRL) msr in any case (also, is that a > cheap msr?) > > Not touching it at all seems silly. > Note that even if we do such programming, it would still be desirable to minimise the number of times we have to reprogram it so the series as it stands would still be useful. -- Mel Gorman SUSE Labs