On 15.03.2022 10:12, Roger Pau Monné wrote: > On Mon, Mar 14, 2022 at 05:19:37PM +0100, Jan Beulich wrote: >> One thing seems quite clear though: Doing any of this with interrupts >> enabled increases the chances for the read pairs to not properly >> correlate, due to an interrupt happening in the middle. This alone is >> a reason for me to want to keep IRQs off here. > > Right, TSC calibration is also done with interrupts disabled, so it > does seem correct to do the same here for APIC. > > Maybe it would be cleaner to hide the specific PIT logic in > calibrate_apic_timer() so that we could remove get_8254_timer_count() > and wait_8254_wraparound() from apic.c and apic.c doesn't have any PIT > specific code anymore?
Yes, that's certainly a further cleanup step to take (saying this without actually having tried, so there may be obstacles). Jan > I think using channel 2 like it's used for the TSC calibration won't > be possible at this point, since it will skew read_pit_count() users? > In any case if we disable interrupts those will already be skewed > because the timer won't be rearmed until interrupts are enabled. > > Thanks, Roger. >
