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

[Thomas Gleixner]

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