From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751886AbeA2PdW (ORCPT ); Mon, 29 Jan 2018 10:33:22 -0500 Received: from mx1.redhat.com ([209.132.183.28]:43354 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751256AbeA2PdV (ORCPT ); Mon, 29 Jan 2018 10:33:21 -0500 Date: Mon, 29 Jan 2018 10:33:16 -0500 From: Luiz Capitulino To: Frederic Weisbecker Cc: Ingo Molnar , LKML , Peter Zijlstra , Chris Metcalf , Thomas Gleixner , Christoph Lameter , "Paul E . McKenney" , Wanpeng Li , Mike Galbraith , Rik van Riel Subject: Re: [GIT PULL] isolation: 1Hz residual tick offloading v4 Message-ID: <20180129103316.4d2f9153@redhat.com> In-Reply-To: <20180129011024.GA2942@lerouge> References: <1516320140-13189-1-git-send-email-frederic@kernel.org> <20180124104608.038fb212@redhat.com> <20180129011024.GA2942@lerouge> Organization: Red Hat MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, 29 Jan 2018 02:10:26 +0100 Frederic Weisbecker wrote: > On Wed, Jan 24, 2018 at 10:46:08AM -0500, Luiz Capitulino wrote: > > On Fri, 19 Jan 2018 01:02:14 +0100 > > Frederic Weisbecker wrote: > > > > > Ingo, > > > > > > Please pull the sched/0hz-v2 branch that can be found at: > > > > > > git://git.kernel.org/pub/scm/linux/kernel/git/frederic/linux-dynticks.git > > > sched/0hz-v2 > > > > > > HEAD: 9b14d5204490f9acd03998a5e406ecadb87cddba > > > > > > Changes in v4: > > > > > > * Remove the nohz_offload option, just stick with the existing interface, > > > the change is transparent. Suggested by Luiz. > > > > > > * Automatically pin workqueues to housekeepers. > > > > I've been testing this series and the tick doesn't go completely away > > for me: it ticks at around 8 seconds interval. > > > > I've debugged this down to the clocksource_watchdog() timer, which is > > created by clocksource_start_watchdog(). This timer cycles over all online > > CPUs. I couldn't find a way to disable it. It seems to be always enabled > > for x86 by CONFIG_CLOCKSOURCE_WATCHDOG since commit 6471b825c4. > > > > Since the 1Hz tick offload worked for you, I must be missing a way > > to disable this timer or the kernel is thinking my CPU has unstable > > TSC (which it doesn't AFAIK). > > It's beyond the scope of this patchset but indeed that's right, I run my > kernels with tsc=reliable because my CPUs don't have the TSC_RELIABLE flag. > That's the only way I found to shutdown the tick completely on my test > machine, otherwise I keep having that clocksource watchdog. > > You can try "tsc=reliable" but that's at your own risks and it's hard > to tell what exactly are those risks depending on your CPU model (and > perhaps BIOS?). Cool, passing tsc=reliable worked for me. I finally got to the tick to go completely away. While I agree that fixing that is beyond the scope of this series, I think we should improve it anyway since it will probably come up for people trying the new nohz_full=. If this has any value: Tested-by: Luiz Capitulino > You likely already had that watchdog timer before this patchset but didn't > notice because the 1Hz was a more frequent annoyance. That's possible, but I'm not sure the clocksource watchdog timer was there before commit 6471b825c4.