Messages in this thread | | | Date | Mon, 29 Jan 2018 10:33:16 -0500 | From | Luiz Capitulino <> | Subject | Re: [GIT PULL] isolation: 1Hz residual tick offloading v4 |
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On Mon, 29 Jan 2018 02:10:26 +0100 Frederic Weisbecker <frederic@kernel.org> 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 <frederic@kernel.org> 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 <lcapitulino@redhat.com>
> 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.
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