my comment was about your comment that MSR have wrapped however many times
> On Apr 1, 2016, at 10:03 AM, Peter Zijlstra <[email protected]> wrote: > > That is; if userspace doesn't request a freq reading we can go without > reading this for a very long time. > >> + >> + rdmsrl(MSR_IA32_APERF, aperf); >> + rdmsrl(MSR_IA32_MPERF, mperf); >> + >> + aperf_delta = aperf - s->aperf; >> + mperf_delta = mperf - s->mperf; > > That means these delta's can be arbitrarily large, in fact the MSRs can > have wrapped however many times. The MSRs will not wrap that often. — Steph > On Apr 1, 2016, at 10:29 AM, Peter Zijlstra <[email protected]> wrote: > > On Fri, Apr 01, 2016 at 10:23:23AM +0200, Peter Zijlstra wrote: >> >> Trim your emails >> >> On Fri, Apr 01, 2016 at 10:16:42AM +0200, Stephane Gasparini wrote: >> >>>> That means these delta's can be arbitrarily large, in fact the MSRs can >>>> have wrapped however many times. >>> >>> 64 bits is 18 446 744 073 709 551 615 >>> >>> so even assuming a 10 GHz frequency if my math are good this is more than >>> 58 years before the MSR wrap around, assuming the device ran always at max >>> freq. >> >> fair enough.. but going with 10Ghz, cpu_khz would be 10e6 ~ 33 bits, > > I can't do maths this morning; 23 bits > >> which effectively reduces the wrap/overflow time to just 31 bits, which >> per that frequency is just ~1/4th of a second. > > 41 giving lots more, but a reasonable time to wrap/overflow. > -- > To unsubscribe from this list: send the line "unsubscribe linux-pm" in > the body of a message to [email protected] > More majordomo info at http://vger.kernel.org/majordomo-info.html
