Messages in this thread | | | Date | Wed, 16 May 2018 09:22:02 +0200 | From | Peter Zijlstra <> | Subject | Re: [RFC/RFT] [PATCH 03/10] cpufreq: intel_pstate: Utility functions to boost HWP performance limits |
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On Tue, May 15, 2018 at 09:49:04PM -0700, Srinivas Pandruvada wrote: > Setup necessary infrastructure to be able to boost HWP performance on a > remote CPU. First initialize data structure to be able to use > smp_call_function_single_async(). The boost up function simply set HWP > min to HWP max value and EPP to 0. The boost down function simply restores > to last cached HWP Request value. > > To avoid reading HWP Request MSR during dynamic update, the HWP Request > MSR value is cached in the local memory. This caching is done whenever > HWP request MSR is modified during driver init on in setpolicy() callback > path.
The patch does two independent things; best to split that.
> diff --git a/drivers/cpufreq/intel_pstate.c b/drivers/cpufreq/intel_pstate.c > index f686bbe..dc7dfa9 100644 > --- a/drivers/cpufreq/intel_pstate.c > +++ b/drivers/cpufreq/intel_pstate.c > @@ -221,6 +221,9 @@ struct global_params { > * preference/bias > * @epp_saved: Saved EPP/EPB during system suspend or CPU offline > * operation > + * @hwp_req_cached: Cached value of the last HWP request MSR
That's simply not true given the code below.
> @@ -763,6 +768,7 @@ static void intel_pstate_hwp_set(unsigned int cpu) > intel_pstate_set_epb(cpu, epp); > } > skip_epp: > + cpu_data->hwp_req_cached = value; > wrmsrl_on_cpu(cpu, MSR_HWP_REQUEST, value); > } > > @@ -1381,6 +1387,39 @@ static void intel_pstate_get_cpu_pstates(struct cpudata *cpu) > intel_pstate_set_min_pstate(cpu); > } > > + > +static inline void intel_pstate_hwp_boost_up(struct cpudata *cpu) > +{ > + u64 hwp_req; > + u8 max; > + > + max = (u8) (cpu->hwp_req_cached >> 8); > + > + hwp_req = cpu->hwp_req_cached & ~GENMASK_ULL(31, 24); > + hwp_req = (hwp_req & ~GENMASK_ULL(7, 0)) | max; > + > + wrmsrl(MSR_HWP_REQUEST, hwp_req); > +} > + > +static inline void intel_pstate_hwp_boost_down(struct cpudata *cpu) > +{ > + wrmsrl(MSR_HWP_REQUEST, cpu->hwp_req_cached); > +}
This is not a traditional msr shadow; that would be updated on every wrmsr. There is not a comment in sight explaining why this one is different.
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