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Date: Wed, 29 Mar 2017 14:56:37 +0200 From: Frederic Weisbecker <fweisbec@...il.com> To: Wanpeng Li <kernellwp@...il.com> Cc: Luiz Capitulino <lcapitulino@...hat.com>, Rik van Riel <riel@...hat.com>, "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org> Subject: Re: [BUG nohz]: wrong user and system time accounting On Wed, Mar 29, 2017 at 05:56:30PM +0800, Wanpeng Li wrote: > 2017-03-29 5:26 GMT+08:00 Luiz Capitulino <lcapitulino@...hat.com>: > > On Tue, 28 Mar 2017 17:01:52 -0400 > > Rik van Riel <riel@...hat.com> wrote: > > > >> On Tue, 2017-03-28 at 16:14 -0400, Luiz Capitulino wrote: > >> > On Tue, 28 Mar 2017 13:24:06 -0400 > >> > Luiz Capitulino <lcapitulino@...hat.com> wrote: > >> > > I'm starting to suspect that the nohz code may be programming > >> > > the tick period to be shorter than 1ms when it re-activates > >> > > the tick. > >> > > >> > And I think I was right, it looks like the nohz code is programming > >> > the tick period incorrectly when restarting the tick. The patch below > >> > fixes things for me, but I still have some homework todo and more > >> > testing before posting a patch for inclusion. Could you guys test it? > >> > >> Your patch seems to work. I don't claim to understand why > >> your patch makes a difference, but for this particular test > >> case, on this particular setup, it seems to work... > > > > I don't fully understand why either yet. I was looking for places > > where nohz might be programming the tick period incorrectly and > > The bug is still present when I config CONTEXT_TRACKING_FORCE and > nohz=off in the boot parameter. Indeed I saw something similar a few days ago with: !CONFIG_NO_HZ_FULL && CONFIG_VIRT_CPU_ACCOUNTING_GEN && CONTEXT_TRACKING_FORCE And it disappeared with CONFIG_NO_HZ_FULL=y so I didn't care much because that setting isn't used in production and in fact I intend to remove CONTEXT_TRACKING_FORCE. But it could be the sign of something important. It might be different than Luiz's bug because I can't reproduce his bug yet even with his config.
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