Re: clocksource_watchdog causing scheduling of timers every second (was [v13] support "task_isolation" mode)

On Thu, Aug 11, 2016 at 06:02:34PM -0500, Christoph Lameter wrote:

On Thu, 11 Aug 2016, Paul E. McKenney wrote:

quoted

quoted

With modern Intel we could run it on one CPU per package I think, but at
the same time, too much in NOHZ_FULL assumes the TSC is indeed sane so
it doesn't make sense to me to keep the watchdog running, when it
triggers it would also have to kill all NOHZ_FULL stuff, which would
probably bring the entire machine down..

Well, you -could- force a very low priority CPU-bound task to run on
all nohz_full CPUs.  Not necessarily a good idea, but a relatively
non-intrusive response to that particular error condition.

Given that we want the cpu only to run the user task I would think that is
not a good idea.

Heh!  The only really good idea is for clocks to be reliably in sync.

But if they go out of sync, what do you want to do instead?

							Thanx, Paul