Re: [LKP] Re: [clocksource] 6c52b5f3cf: stress-ng.opcode.ops_per_sec -14.4% regression

Thomas Gleixner
2021-04-23T19:14:52Z

On Thu, Apr 22 2021 at 07:24, Paul E. McKenney wrote:
> On Thu, Apr 22, 2021 at 03:41:26PM +0800, Feng Tang wrote:
> So what are our options?
>
> 1. Clear CLOCK_SOURCE_MUST_VERIFY from tsc-early.
>
> 2. #1, but add tsc-early into the watchdog list and set
> CLOCK_SOURCE_MUST_VERIFY once it is better calibrated.
>
> 3. Add a field to struct clocksource that, if non-zero, gives
> the maximum drift in nanoseconds per half second (AKA
> WATCHDOG_INTERVAL). If zero, the WATCHDOG_MAX_SKEW value
> is used. Set this to (say) 150,000ns for tsc-early.
>
> 4. As noted earlier, increase WATCHDOG_MAX_SKEW to 150 microseconds,
> which again is not a good approach given the real-world needs
> of real-world applications.
>
> 5. Your ideas here.

#3 or add a flag to the clocksource which says 'frequency is guesswork' and
increase the threshold based on that.

If that flag is still set max_drift is != 0 after 20 seconds yell.

Thanks,

tglx