Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752467AbaKJTkX (ORCPT ); Mon, 10 Nov 2014 14:40:23 -0500 Received: from mail-lb0-f180.google.com ([209.85.217.180]:51591 "EHLO mail-lb0-f180.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751385AbaKJTkU convert rfc822-to-8bit (ORCPT ); Mon, 10 Nov 2014 14:40:20 -0500 MIME-Version: 1.0 In-Reply-To: <20141107064027.GA24745@yliu-dev.sh.intel.com> References: <20141107060040.GD30507@yliu-dev.sh.intel.com> <20141107064027.GA24745@yliu-dev.sh.intel.com> From: Andy Lutomirski Date: Mon, 10 Nov 2014 11:39:56 -0800 Message-ID: Subject: Re: [LKP] [x86_64,entry] f04e05b81e4: -62.7% time.user_time To: Yuanhan Liu Cc: LKP , LKML Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8BIT Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Nov 6, 2014 at 10:40 PM, Yuanhan Liu wrote: > On Thu, Nov 06, 2014 at 10:26:23PM -0800, Andy Lutomirski wrote: >> On Thu, Nov 6, 2014 at 10:00 PM, LKP wrote: >> > FYI, we noticed the below changes on >> > >> > git://git.kernel.org/pub/scm/linux/kernel/git/luto/linux.git x86/entry >> > commit f04e05b81e4d9ae88bee379f12176f551a24394a ("x86_64,entry: Use sysret to return to userspace when possible") >> > >> > >> > f2ee9bebb99dd4a4 f04e05b81e4d9ae88bee379f12 testbox/testcase/testparams >> > ---------------- -------------------------- >> > %stddev %change %stddev >> > \ | \ >> > 24.09 ą 4% -62.7% 8.99 ą 3% lkp-wsx02/aim9/performance-300s-creat-clo >> > 24.09 -62.7% 8.99 GEO-MEAN time.user_time >> > >> >> I don't really know how to interpret this. Is this a good thing or a bad thing? > > TBH, I don't, either. Here we just list the changes we captured, which > is then for your information to decide it's good or bad. > >> >> I actually expect this change to be a dramatic speedup for some >> workloads. > > Would you like to share your workload? If so, I can add them to our > testing system, and give feedback to you when datat is available. My workload is just syscall performance under different conditions. There's no obvious interesting benchmark, although I may write one at some point. > >> Any chance you can send me the .config, kernel command >> line, and whether you have any tracing features enabled? > > .config and dmesg are attached. Hmm. I'm not entirely sure what's going on. I think that you have NO_HZ_FULL active, but I can't see what's actually activating it. My initial attempt to replicate this failed, but I see a big performance gain if CONFIG_CONTEXT_TRACKING_FORCE=y, so I suspect that you've just managed to activate context tracking without forcing it. --Andy -- 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/