Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756713Ab2EVJBT (ORCPT ); Tue, 22 May 2012 05:01:19 -0400 Received: from casper.infradead.org ([85.118.1.10]:51335 "EHLO casper.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754944Ab2EVJBR convert rfc822-to-8bit (ORCPT ); Tue, 22 May 2012 05:01:17 -0400 Message-ID: <1337677268.9698.6.camel@twins> Subject: Re: [PATCH 0/2] RFC: readd fair sleepers for server systems From: Peter Zijlstra To: Martin Schwidefsky Cc: Ingo Molnar , Mike Galbraith , linux-kernel@vger.kernel.org, Heiko Carstens , Christian Ehrhardt Date: Tue, 22 May 2012 11:01:08 +0200 In-Reply-To: <1337615137-55111-1-git-send-email-schwidefsky@de.ibm.com> References: <1337615137-55111-1-git-send-email-schwidefsky@de.ibm.com> Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7BIT X-Mailer: Evolution 3.2.2- Mime-Version: 1.0 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1600 Lines: 38 On Mon, 2012-05-21 at 17:45 +0200, Martin Schwidefsky wrote: > our performance team found a performance degradation with a recent > distribution update in regard to fair sleepers (or the lack of fair > sleepers). On s390 we used to run with fair sleepers disabled. This change was made a very long time ago.. tell your people to mind what upstream does if they want us to mind them. Also, reports like this make me want to make /debug/sched_features a patch in tip/out-of-tree so that its never available outside development. > We see the performance degradation with our network benchmark and fair > sleepers enabled, the largest hit is on virtual connections: > > VM guest Hipersockets > Throughput degrades up to 18% > CPU load/cost increase up to 17% > VM stream > Throughput degrades up to 15% > CPU load/cost increase up to 22% > LPAR Hipersockets > Throughput degrades up to 27% > CPU load/cost increase up to 20% Why is this, is this some weird interaction with your hypervisor? > In short, we want the fair sleepers tunable back. I understand that on > x86 we want to avoid the cost of a branch on the hot path in place_entity, > therefore add a compile time config option for the fair sleeper control. I'm very much not liking this... this makes s390 schedule completely different from all the other architectures. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/