Andi, On Fri, Aug 30, 2019 at 5:31 PM Andi Kleen <a...@linux.intel.com> wrote: > > > the same manner. It would greatly simplify the kernel implementation. > > I tried that originally. It was actually more complicated. > > You can't really do deltas on raw metrics, and a lot of the perf > infrastructure is built around deltas. > How is RAPL handled? No deltas there either. It uses the snapshot model. At each interval, perf stat just reads the current count, and does not compute a delta since previous read. With PERF_METRICS, the delta is always since previous read. If you read frequently enough you do not lose precision.
> > To do the regular reset and not lose precision over time internally > you have to keep expanded counters anyways. And if you do that > you can just expose them to user space too, and have everything > in user space just work without any changes (except for the final > output) > > -Andi >
