Hi Vince, Thanks for asking.
On Wed, Jun 15, 2016 at 09:13:59PM -0400, Vince Weaver wrote: > > three questions about this functionality: > > 1. In theory this should also work on an amd fam16h model 30h > processor too, correct? The current code limits things to fam15h > even though the fam16mod30h has all the proper cpuid flags. > I was told this feature would be supported on fam15h 60h, 70h and later processors before. Just checked the fam16h model 30h BKDG, yes, it should be also supported. But I didn't test that platform, if you confirm it works in your side. We can enable it. > I've tested the functionality a bit and it seems to work but for > some reason the ptsc seems to occasionally count backwards > on my machine. Any reason that would be? (It doesn't seem to be > an overflow, just reading the ptsc 5ms apart and the values are > slightly lower after than before). > PTSC's frequency is about 100Mhz, it shouldn't be overflow. > 2. Unless I'm misunderstanding things, the code seems to be accumulating > Power. (see chunk below) Power is an instantaneous measurement, it > makes no sense to add values. If you use 5W for 1ms and 10W for > 1ms, the average power across the 2ms interval is not 15W. > > You can add energy, but not power. > > > + delta *= cpu_pwr_sample_ratio * 1000; > > + tdelta = new_ptsc - prev_ptsc; > > + > > + do_div(delta, tdelta); > > + local64_add(delta, &event->count); > You're right. Nice catch! The average power is per compute unit. We cannot add the power simplely for each processor/package. So here, the average power per package should be (delta1 + delta2 + ... + deltaN)/(tdelta_avg). I will work out a fix. Thanks to point out. > 3. The actual results gathered seem rediculously low. 341 seconds of > calculation and only using 183 mWatts of power? > mWatts are for processor power not system power. Below data is calculated on fam15h model 60h which is low power platform. Even though the method has a minor mistake, the processor power should be in mWatts field. > > Performance counter stats for 'system wide': > > > > 183.44 mWatts power/power-pkg/ > > > > 341.837270111 seconds time elapsed > > > > root@hr-zp:/home/ray/tip# ./tools/perf/perf stat -a -e 'power/power-pkg/' > > sleep 10 > Thanks, Rui
