Re: [PATCH] Fix /proc/stat freezes (was [PATCH v15] "task_isolation" mode)

[Chris Metcalf]

On 8/17/2016 3:37 PM, Christoph Lameter wrote:
> On Tue, 16 Aug 2016, Chris Metcalf wrote:
>
> > - Dropped Christoph Lameter's patch to avoid scheduling the
> >    clocksource watchdog on nohz cores; the recommendation is to just
> >    boot with tsc=reliable for NOHZ in any case, if necessary.
> We also said that there should be a WARN_ON if tsc=reliable is not
> specified and processors are put into NOHZ mode. This is something not
> obvious causing scheduling events on NOHZ processors.

Yes, I agree.  Frederic said he would queue a patch to do that, so I
didn't want to propose another patch that would conflict.

> > Frederic, do you have a sense of what is left to be done there?
> > I can certainly try to contribute to that effort as well.
> Here is a potential fix to the problem that /proc/stat values freeze when
> processors go into NOHZ busy mode. I'd like to hear what people think
> about the approach here. In particular one issue may be that I am
> accessing remote tick-sched structures without serialization. But for
> top/ps this may be ok. I noticed that other values shown by top/os also
> sometime are a bit fuzzy.

This seems pretty plausible to me, but I'm not an expert on what kind
of locking might be required for these data structures.

--
Chris Metcalf, Mellanox Technologies
http://www.mellanox.com