Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S936278Ab3DJNrg (ORCPT ); Wed, 10 Apr 2013 09:47:36 -0400 Received: from mail-la0-f54.google.com ([209.85.215.54]:57916 "EHLO mail-la0-f54.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1759692Ab3DJNre (ORCPT ); Wed, 10 Apr 2013 09:47:34 -0400 MIME-Version: 1.0 In-Reply-To: <0000013dd63de989-c6980852-2aac-4597-ba34-3b2efaa24c17-000000@email.amazonses.com> References: <1364993190-13784-1-git-send-email-fweisbec@gmail.com> <0000013dd63de989-c6980852-2aac-4597-ba34-3b2efaa24c17-000000@email.amazonses.com> Date: Wed, 10 Apr 2013 15:47:33 +0200 Message-ID: Subject: Re: [RFC GIT PULL] nohz: Kconfig layout improvements From: Frederic Weisbecker To: Christoph Lameter Cc: Ingo Molnar , LKML , Andrew Morton , Chris Metcalf , Geoff Levand , Gilad Ben Yossef , Hakan Akkan , Kevin Hilman , Li Zhong , Namhyung Kim , "Paul E. McKenney" , Paul Gortmaker , Peter Zijlstra , Steven Rostedt , Thomas Gleixner , Michal Marek Content-Type: text/plain; charset=ISO-8859-1 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2361 Lines: 60 2013/4/4 Christoph Lameter : > It seems that nohz still has no effect. > > 3.9-rc5 + patches. Affinity of init set to 0,1 so no > tasks are running on 9. The "latencytest" used here is part of my > lldiag-0.15 toolkit. > > First test without any special kernel parameters. nohz off right? > > $ nice -5 taskset -c 9 latencytest > > CPUs: Freq=2.90Ghz Processors=32 Cores=8 cacheline_size=64 Intel(R) > Xeon(R) CPU E5-2690 0 @ 2.90GHz > 16775106 samples below 1000 nsec > 13 involuntary context switches > 1019 (0.00607411%) variances in 10.00 seconds: minimum 1.07us maximum 12.32us average 3.30us stddev 0.63us > > HZ=100 so the 1019 variances are likely timer interrupts. > > > > > After nohz setup > > /proc/cmdline: > > BOOT_IMAGE=/vmlinuz-3.9.0-rc5+ root=/dev/mapper/vg01-root ro console=tty0 console=ttyS0,115200 idle=mwait rcu_nocb_poll rcu_nocbs=2-31 nohz_extended=2-31 > > $ nice -5 taskset -c 9 latencytest > CPUs: Freq=2.90Ghz Processors=32 Cores=8 cacheline_size=64 Intel(R) > Xeon(R) CPU E5-2690 0 @ 2.90GHz > 16779362 samples below 1000 nsec > 13 involuntary context switches > 1037 (0.00617983%) variances in 10.00 seconds: minimum 1.00us maximum 10.61us average 3.30us stddev 0.98us > > > > If I move the RCU threads off the cpu then I get a slightly better result: > > $ nice -5 taskset -c 9 latencytest > CPUs: Freq=2.90Ghz Processors=32 Cores=8 cacheline_size=64 Intel(R) > Xeon(R) CPU E5-2690 0 @ 2.90GHz > 16796039 samples below 1000 nsec > 12 involuntary context switches > 1020 (0.00607249%) variances in 10.00 seconds: minimum 1.00us maximum 11.58us average 2.77us stddev 0.55us > > > > Why is the tick not stopping? How do I diagnose this? (I can start > patching the kernel again like last time but isnt there a better way?) I don't know which tree you are using. But if you have that patch in: http://git.kernel.org/cgit/linux/kernel/git/frederic/linux-dynticks.git/commit/?h=3.9-rc1-nohz1&id=451128553e5e827dccc6cbcd24238470ec693d90 looking at the traces on that CPU may give you a few hints. Then you can dig deeper by looking at the sched_switch, timers, irq, ... events -- 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/