Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755551Ab2EUPqR (ORCPT ); Mon, 21 May 2012 11:46:17 -0400 Received: from e06smtp14.uk.ibm.com ([195.75.94.110]:42919 "EHLO e06smtp14.uk.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755145Ab2EUPqP (ORCPT ); Mon, 21 May 2012 11:46:15 -0400 From: Martin Schwidefsky To: Peter Zijlstra , Ingo Molnar , Mike Galbraith , linux-kernel@vger.kernel.org Cc: Heiko Carstens , Christian Ehrhardt , Martin Schwidefsky Subject: [PATCH 0/2] RFC: readd fair sleepers for server systems Date: Mon, 21 May 2012 17:45:35 +0200 Message-Id: <1337615137-55111-1-git-send-email-schwidefsky@de.ibm.com> X-Mailer: git-send-email 1.7.10.2 x-cbid: 12052115-1948-0000-0000-000001DC50E4 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1669 Lines: 47 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. 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% Real world workloads are also affected, e.g. we see degrations with oltp database workloads. Christian has the numbers if needed. The only workload on s390 with a performance benefit with fair sleepers enabled are some J2EE workloads, but only in the <2% area. 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. blue skies, Martin Martin Schwidefsky (2): sched: readd FAIR_SLEEPERS feature sched: enable FAIR_SLEEPERS for s390 arch/s390/Kconfig | 1 + init/Kconfig | 3 +++ kernel/sched/fair.c | 14 +++++++++++++- kernel/sched/features.h | 9 +++++++++ 4 files changed, 26 insertions(+), 1 deletion(-) -- 1.7.10.2 -- 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/