On 8/17/2016 3:37 PM, Christoph Lameter wrote:

On Tue, 16 Aug 2016, Chris Metcalf wrote:

quoted

- 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.

quoted

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