On Fri, Jan 19, 2018 at 12:24:17PM -0800, Andi Kleen wrote: > > Oh, think a bit more. > > I think we cannot do the same thing as we did for CPU PMU's fixed counters. > > > > The counters here are free running counters. They cannot be start/stop. > > Yes free running counter have completely different semantics. They > need a separate event code.
The only thing that matters is if they count the same thing or not. The not start/stop thing is not important. See arch/x86/events/msr.c on how to deal with that. The short story is that you simply ignore stop and update the prev_count on start. Then any next update will increment with the correct delta. (if the counter is short you also need to run a timer to deal with wraps).
