From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1759523AbbJ3Pfs (ORCPT ); Fri, 30 Oct 2015 11:35:48 -0400 Received: from foss.arm.com ([217.140.101.70]:44428 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751024AbbJ3Pfr (ORCPT ); Fri, 30 Oct 2015 11:35:47 -0400 Date: Fri, 30 Oct 2015 15:35:43 +0000 From: Catalin Marinas To: Dietmar Eggemann Cc: Will Deacon , linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org Subject: Re: [PATCH] ARM64: Enable multi-core scheduler support by default Message-ID: <20151030153543.GY8899@e104818-lin.cambridge.arm.com> References: <1445273749-16778-1-git-send-email-dietmar.eggemann@arm.com> <20151029171944.GS8899@e104818-lin.cambridge.arm.com> <5633628C.1010200@arm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <5633628C.1010200@arm.com> User-Agent: Mutt/1.5.23 (2014-03-12) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Oct 30, 2015 at 12:29:00PM +0000, Dietmar Eggemann wrote: > On 10/29/2015 05:19 PM, Catalin Marinas wrote: > >On Mon, Oct 19, 2015 at 05:55:49PM +0100, Dietmar Eggemann wrote: > >>Make sure that the task scheduler domain hierarchy is set-up correctly > >>on systems with single or multi-cluster topology. > >> > >>Signed-off-by: Dietmar Eggemann > >>--- > >> arch/arm64/configs/defconfig | 1 + > >> 1 file changed, 1 insertion(+) > >> > >>diff --git a/arch/arm64/configs/defconfig b/arch/arm64/configs/defconfig > >>index 34d71dd86781..dc70d715bc38 100644 > >>--- a/arch/arm64/configs/defconfig > >>+++ b/arch/arm64/configs/defconfig > >>@@ -51,6 +51,7 @@ CONFIG_PCI=y > >> CONFIG_PCI_MSI=y > >> CONFIG_PCI_XGENE=y > >> CONFIG_SMP=y > >>+CONFIG_SCHED_MC=y > >> CONFIG_PREEMPT=y > >> CONFIG_KSM=y > >> CONFIG_TRANSPARENT_HUGEPAGE=y > > > >Question: does enabling this option have any (positive) effect on the > >vanilla kernel or it requires additional patches like EAS? > > It improves the task scheduler decisions on multi-cluster systems. You have > to iterate over all cpu's less frequently when gathering the sched group > statistics e.g. during CFS load-balancing. > > You essentially replace a flat (all cpus) with an hierarchical approach > (lowest level: sched group eq. cpu, next level: sched group eq. cluster) and > do CFS load balancing frequently between two cpu's of the same cluster > (lowest level) and less frequently between two cpus from different cluster. > > Not sure that I would see an effect on the performance score on a JUNO board > when running hackbench. Could give it a try ... Probably easier to spot on a > machine with >32 logical cpus. I did some tests on Juno last week with and without this option and I haven't noticed any difference. Anyway, thanks for the explanation. Patch applied. -- Catalin