From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752674AbcBOJBg (ORCPT ); Mon, 15 Feb 2016 04:01:36 -0500 Received: from mail-wm0-f66.google.com ([74.125.82.66]:35865 "EHLO mail-wm0-f66.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752496AbcBOJBe (ORCPT ); Mon, 15 Feb 2016 04:01:34 -0500 Message-ID: <1455526889.11761.23.camel@gmail.com> Subject: Re: [PATCH 0/4 v6] sched,time: reduce nohz_full syscall overhead 40% From: Mike Galbraith To: riel@redhat.com, linux-kernel@vger.kernel.org Cc: fweisbec@gmail.com, tglx@linutronix.de, mingo@kernel.org, luto@amacapital.net, peterz@infradead.org, clark@redhat.com, eric.dumazet@gmail.com Date: Mon, 15 Feb 2016 10:01:29 +0100 In-Reply-To: <1455152907-18495-1-git-send-email-riel@redhat.com> References: <1455152907-18495-1-git-send-email-riel@redhat.com> Content-Type: text/plain; charset="UTF-8" X-Mailer: Evolution 3.16.5 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 Hi Rik, On Wed, 2016-02-10 at 20:08 -0500, riel@redhat.com wrote: > I tested this series with a microbenchmark calling > an invalid syscall number ten million times in a row, > on a nohz_full cpu. > > Run times for the microbenchmark: > > 4.4 3.8 seconds > 4.5-rc1 3.7 seconds > 4.5-rc1 + first patch 3.3 seconds > 4.5-rc1 + first 3 patches 3.1 seconds > 4.5-rc1 + all patches 2.3 seconds > > Same test on a non-NOHZ_FULL, non-housekeeping CPU: > all kernels 1.86 seconds I tested 10M stat(".", &buf) calls, and saw a win of ~20% on a nohz_full cpu. Below are nopreempt vs nohz_full+patches overhead numbers from my box. avg 4.4.1-nopreempt 0m1.652s 0m1.633s 0m1.635s 1.640 1.000 nohz_full + patches nohz_full inactive 0m1.642s 0m1.631s 0m1.629s 1.634 .996 housekeeper CPU 0m2.013s 0m2.012s 0m2.033s 2.019 1.231 nohz_full CPU 0m2.247s 0m2.233s 0m2.239s 2.239 1.365 It still ain't free ;-) but between this set, and all the other work that has gone in ~recently, it looks one hell of a lot better. That's not too scary a pricetag. -Mike