From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752022AbbJOIrL (ORCPT ); Thu, 15 Oct 2015 04:47:11 -0400 Received: from mail-wi0-f170.google.com ([209.85.212.170]:36051 "EHLO mail-wi0-f170.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750880AbbJOIrI (ORCPT ); Thu, 15 Oct 2015 04:47:08 -0400 Date: Thu, 15 Oct 2015 10:47:02 +0200 From: Ingo Molnar To: Jason Low Cc: Peter Zijlstra , Thomas Gleixner , linux-kernel@vger.kernel.org, Oleg Nesterov , "Paul E. McKenney" , Frederic Weisbecker , Davidlohr Bueso , Steven Rostedt , Andrew Morton , George Spelvin , hideaki.kimura@hpe.com, terry.rudd@hpe.com, scott.norton@hpe.com Subject: Re: [PATCH v2 0/4] timer: Improve itimers scalability Message-ID: <20151015084702.GA16953@gmail.com> References: <1444849677-29330-1-git-send-email-jason.low2@hp.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1444849677-29330-1-git-send-email-jason.low2@hp.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 * Jason Low wrote: > While running a database workload on a 16 socket machine, there were > scalability issues related to itimers. The following link contains a > more detailed summary of the issues at the application level. > > https://lkml.org/lkml/2015/8/26/737 > > Commit 1018016c706f addressed the issue with the thread_group_cputimer > spinlock taking up a significant portion of total run time. > This patch series addresses the secondary issue where a lot of time is > spent trying to acquire the sighand lock. It was found in some cases > that 200+ threads were simultaneously contending for the same sighand > lock, reducing throughput by more than 30%. > > With this patch set (along with commit 1018016c706f mentioned above), > the performance hit of itimers almost completely goes away on the > 16 socket system. > > Jason Low (4): > timer: Optimize fastpath_timer_check() > timer: Check thread timers only when there are active thread timers > timer: Convert cputimer->running to bool > timer: Reduce unnecessary sighand lock contention > > include/linux/init_task.h | 3 +- > include/linux/sched.h | 9 ++++-- > kernel/fork.c | 2 +- > kernel/time/posix-cpu-timers.c | 63 ++++++++++++++++++++++++++++----------- > 4 files changed, 54 insertions(+), 23 deletions(-) Is there some itimers benchmark that can be used to measure the effects of these changes? Thanks, Ingo