From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Doug Smythies" Subject: RE: Performance of low-cpu utilisation benchmark regressed severely since 4.6 Date: Mon, 24 Apr 2017 07:24:31 -0700 Message-ID: <000001d2bd06$7f29b960$7d7d2c20$@net> References: <20170410084117.rjh3mtdx7hd2i5ze@techsingularity.net> <000a01d2b9e6$393afef0$abb0fcd0$@net> <000301d2bb31$c0037790$400a66b0$@net> <000501d2bc46$ad4b1fc0$07e15f40$@net> 2Sh4dt8AXIBJV2Sh6dNtdh Mime-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 7bit Return-path: Received: from cmta18.telus.net ([209.171.16.91]:57709 "EHLO cmta18.telus.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1171939AbdDXOYj (ORCPT ); Mon, 24 Apr 2017 10:24:39 -0400 In-Reply-To: 2Sh4dt8AXIBJV2Sh6dNtdh Content-Language: en-ca Sender: linux-pm-owner@vger.kernel.org List-Id: linux-pm@vger.kernel.org To: 'Srinivas Pandruvada' , "'Rafael J. Wysocki'" Cc: "'Rafael J. Wysocki'" , 'Mel Gorman' , 'Rafael Wysocki' , =?utf-8?Q?'J=C3=B6rg_Otte'?= , 'Linux Kernel Mailing List' , 'Linux PM' , Doug Smythies On 2017.04.23 18:23 Srinivas Pandruvada wrote: > On Mon, 2017-04-24 at 02:59 +0200, Rafael J. Wysocki wrote: >> On Sun, Apr 23, 2017 at 5:31 PM, Doug Smythies wrote: >>> It looks like the cost is mostly related to moving the load from >>> one CPU to >>> another and waiting for the new one to ramp up then. > Last time when we analyzed Mel's result last year this was the > conclusion. The problem was more apparent on systems with per core P- > state. ?? I have never seen this particular use case before. Unless I have looked the wrong thing, Mel's issue last year was a different use case. ...[cut]... >>>> We can do one more trick I forgot about. Namely, if we are about >>>> to increase >>>> the P-state, we can jump to the average between the target and >>>> the max >>>> instead of just the target, like in the appended patch (on top of >>>> linux-next). >>>> >>>> That will make the P-state selection really aggressive, so costly >>>> energetically, >>>> but it shoud small jumps of the average load above 0 to case big >>>> jumps of >>>> the target P-state. >>> I'm already seeing the energy costs of some of this stuff. >>> 3050.2 Seconds. >> Is this with or without reducing the sampling interval? It was without reducing the sample interval. So, it was the branch you referred us to the other day: git://git.kernel.org/pub/scm/linux/kernel/git/rafael/linux-pm.git linux-next with your patch (now deleted from this thread) applied. ...[cut]... >> Anyway, your results are somewhat counter-intuitive. >> Would it be possible to run this workload with the linux-next branch >> and the schedutil governor and see if the patch at >> https://patchwork.kernel.org/patch/9671829/ makes any difference? git://git.kernel.org/pub/scm/linux/kernel/git/rafael/linux-pm.git linux-next Plus that patch is in progress. ... Doug