On Wed, 24 May 2017, Andi Kleen wrote: > > Right, I did not even consider the rdpmc, but yeah, you will get a count > > that > > is not relevant to the user visible event. Unless you fake it using the time > > scaling fields there but that's ugly. > > Could add another scaling field to the mmap page for this.
The whole point of the rdpmc() implementation is to be low overhead. If you have to parse 10 different mmap() fields it starts to defeat the purpose. I already have people really grumpy that you have to have one mmap() page per event, meaning you sacrifice one TLB entry for each event you are measuring. If the watchdog counter is constantly running, can't you just modify perf_event to just grab start/stop values at context switch time and provide the difference to the user? Sort of like the "always running" patchsets that float around? Though I guess that doesn't help much with sampling. Vince
