On Tuesday, April 29, 2014 08:46:05 PM Stratos Karafotis wrote: > According to Intel 64 and IA-32 Architectures SDM, Volume 3, > Chapter 14.2, "Software needs to exercise care to avoid delays > between the two RDMSRs (for example interrupts)". > > So, disable interrupts during reading MSRs IA32_APERF and IA32_MPERF. > Since the TSC is also takes place in the calculation include it in > the protected section. This should increase the accuracy of the > calculations. > > Tested on Intel i7-3770 CPU @ 3.40GHz. > Benchmarks (Phoronix Linux compilation) show a slightly increase > in performance by ~0.1% and a decrease in power consumption by > ~0.13%. > > Signed-off-by: Stratos Karafotis <stratosk@xxxxxxxxxxxx> This looks good to me, but I need Dirk Brandewie to review and comment all intel_pstate patches before I apply any of them. Thanks! > --- > > I hope it's not too inappropriate to post test results in > conjunction with my previous patch about the change of calculation > method of next p-state (https://lkml.org/lkml/2014/4/27/100). > I used Phoronix benchmark - Linux Kernel Compilation 3.1. > Below the test results using turbostat (5 iterations): > > Without 2 patches: > > Ph. avg Time Total time PkgWatt Total Energy > 79.63 266.416 57.74 15382.85984 > 79.63 265.609 57.87 15370.79283 > 79.57 266.994 57.54 15362.83476 > 79.53 265.304 57.83 15342.53032 > 79.71 265.977 57.76 15362.83152 > avg 79.61 266.06 57.74 15364.36985 > > With change calculation patch: > > Ph. avg Time Total time PkgWatt Total Energy > 78.23 258.826 59.14 15306.96964 > 78.41 259.110 59.15 15326.35650 > 78.40 258.530 59.26 15320.48780 > 78.46 258.673 59.20 15313.44160 > 78.19 259.075 59.16 15326.87700 > avg 78.34 258.842 59.18 15318.82650 > > With change calculation patch + this one > > Ph. avg Time Total time PkgWatt Total Energy > 78.33 259.320 59.06 15315.43920 > 78.28 258.245 59.20 15288.10400 > 78.08 257.523 59.32 15276.26436 > 78.38 259.084 59.13 15319.63692 > 78.31 258.232 59.22 15292.49904 > avg 78.27 258.480 59.18 15298.38870 > > > drivers/cpufreq/intel_pstate.c | 3 +++ > 1 file changed, 3 insertions(+) > > diff --git a/drivers/cpufreq/intel_pstate.c b/drivers/cpufreq/intel_pstate.c > index 8e309db..95b3958 100644 > --- a/drivers/cpufreq/intel_pstate.c > +++ b/drivers/cpufreq/intel_pstate.c > @@ -576,10 +576,13 @@ static inline void intel_pstate_sample(struct cpudata *cpu) > { > u64 aperf, mperf; > unsigned long long tsc; > + unsigned long flags; > > + local_irq_save(flags); > rdmsrl(MSR_IA32_APERF, aperf); > rdmsrl(MSR_IA32_MPERF, mperf); > tsc = native_read_tsc(); > + local_irq_restore(flags); > > aperf = aperf >> FRAC_BITS; > mperf = mperf >> FRAC_BITS; > -- I speak only for myself. Rafael J. Wysocki, Intel Open Source Technology Center. -- To unsubscribe from this list: send the line "unsubscribe cpufreq" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
