CMK_TIMER_USE_PPC64 inaccurate with variable clock speeds
The pami-linux-ppc64le machine layer is defaulting to CMK_TIMER_USE_PPC64
src/arch/pami-linux-ppc64le/conv-mach.h:#define CMK_TIMER_USE_PPC64 1
This timer assumes a constant clock speed, which hasn't been true for a long time so projections traces are pretty useless.
Fix the code to do what's necessary to get accurate wall times from the fast intrinsic techniques.
#4 Updated by Ronak Buch 6 months ago
I tried reproducing this on a POWER8 machine and wasn't able to, the timing looked normal.
However, reading through some POWER9 docs makes it seem that there's no guarantee that the time base register update frequency is constant (https://ibm.ent.box.com/s/1hzcwkwf8rbju5h9iyf44wm94amnlcrv. page 898-899, section 6.1).
#7 Updated by Ronak Buch 5 months ago
- Target version changed from 6.9.0 to 6.9.1
I talked to Bilge to get more information about the timers on POWER and if there was any chance that the timer can be guaranteed to update at a fixed frequency. She didn't know and said that she would get back to me with more information.
For now, I'm pushing this to 6.9.1.