From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754608AbeBBUBp (ORCPT ); Fri, 2 Feb 2018 15:01:45 -0500 Received: from mga02.intel.com ([134.134.136.20]:64352 "EHLO mga02.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752291AbeBBUBj (ORCPT ); Fri, 2 Feb 2018 15:01:39 -0500 X-Amp-Result: SKIPPED(no attachment in message) X-Amp-File-Uploaded: False X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.46,450,1511856000"; d="scan'208";a="27628449" Message-ID: <1517601697.83171.361.camel@linux.intel.com> Subject: Re: [PATCH 4/4] sched/fair: Use a recently used CPU as an idle candidate and the basis for SIS From: Srinivas Pandruvada To: Mel Gorman Cc: "Rafael J. Wysocki" , Peter Zijlstra , Mike Galbraith , Matt Fleming , LKML Date: Fri, 02 Feb 2018 12:01:37 -0800 In-Reply-To: <20180202194801.mhvuwzbz6pauf63f@techsingularity.net> References: <20180130104555.4125-1-mgorman@techsingularity.net> <20180201091104.GW2269@hirez.programming.kicks-ass.net> <1517491092.18051.52.camel@linux.intel.com> <2447536.u3g27UoP4q@aspire.rjw.lan> <1517583264.18051.60.camel@linux.intel.com> <20180202194801.mhvuwzbz6pauf63f@techsingularity.net> Content-Type: text/plain; charset="UTF-8" X-Mailer: Evolution 3.24.6 (3.24.6-1.fc26) Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, 2018-02-02 at 19:48 +0000, Mel Gorman wrote: > On Fri, Feb 02, 2018 at 06:54:24AM -0800, Srinivas Pandruvada wrote: > > > > > No idea, desired would be the one I would start with, it > > > > > matches > > > > > with > > > > > the intent here. But I've no idea what our current HWP > > > > > implementation > > > > > actually does with it. > > > > > > > > Desired !=0 will disable HWP autonomous mode of frequency > > > > selection. > > > > > > But I don't think it will just run at "desired" then, will it? > > > > HWP all are these hints only not a guarantee. > > Sure, but the lack on detection when tasks are low utilisation but > still > latency/throughput sensitive is problematic. Users shouldn't have to > know they need to disable HWP or set performance goernor out of the > box. > It's only going to get worse as sockets get larger. I am not saying that we shouldn't do anything. Can you give me some workloads which you care the most? > > > There are totally different way HWP is handled in client an > > servers. > > If you set desired all heuristics they collected will be dumped, so > > they suggest don't set desired when you are in autonomous mode. If > > we > > really want a boost set the EPP. We know that EPP makes lots of > > measurable difference. > > > > Sure boosting EPP makes a difference -- it's essentially what the > performance > goveror does and I know that can be done by a user but it's still > basically a > cop-out. Default performance for low utilisation or lightly loaded > machines > is poor. Maybe it should be set based on the ACPI preferred profile > but > that information is not always available. It would be nice if *some* > sort of hint about new migrations or tasks waking from IO would be > desirable. EPP is a range not a single value. So you don't need to make EPP=0 as a performance governor. PeterZ gave me some scheduler change to experiment, which can be used as hint to play with EPP. Thanks, Srinivas