Messages in this thread | | | From | "Rafael J. Wysocki" <> | Date | Tue, 26 May 2020 10:19:21 +0200 | Subject | Re: [RFC/RFT][PATCH] cpufreq: intel_pstate: Work in passive mode with HWP enabled |
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to On Mon, May 25, 2020 at 10:57 PM Francisco Jerez <francisco.jerez.plata@intel.com> wrote: > > "Rafael J. Wysocki" <rafael@kernel.org> writes: > > > On Mon, May 25, 2020 at 3:39 AM Francisco Jerez > > <francisco.jerez.plata@intel.com> wrote: > >> > >> "Rafael J. Wysocki" <rjw@rjwysocki.net> writes: > >> > >> > From: Rafael J. Wysocki <rafael.j.wysocki@intel.com> > >> > > >> > Allow intel_pstate to work in the passive mode with HWP enabled and > >> > make it translate the target frequency supplied by the cpufreq > >> > governor in use into an EPP value to be written to the HWP request > >> > MSR (high frequencies are mapped to low EPP values that mean more > >> > performance-oriented HWP operation) as a hint for the HWP algorithm > >> > in the processor, so as to prevent it and the CPU scheduler from > >> > working against each other at least when the schedutil governor is > >> > in use. > >> > > >> > Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com> > >> > --- > >> > > >> > This is a prototype not intended for production use (based on linux-next). > >> > > >> > Please test it if you can (on HWP systems, of course) and let me know the > >> > results. > >> > > >> > The INTEL_CPUFREQ_TRANSITION_DELAY_HWP value has been guessed and it very well > >> > may turn out to be either too high or too low for the general use, which is one > >> > reason why getting as much testing coverage as possible is key here. > >> > > >> > If you can play with different INTEL_CPUFREQ_TRANSITION_DELAY_HWP values, > >> > please do so and let me know the conclusions. > >> > > >> > Cheers, > >> > Rafael > >> > > >> > --- > >> > drivers/cpufreq/intel_pstate.c | 169 +++++++++++++++++++++++++++++++---------- > >> > 1 file changed, 131 insertions(+), 38 deletions(-) > >> > > >> > Index: linux-pm/drivers/cpufreq/intel_pstate.c > >> > =================================================================== > >> > --- linux-pm.orig/drivers/cpufreq/intel_pstate.c > >> > +++ linux-pm/drivers/cpufreq/intel_pstate.c > >> > @@ -36,6 +36,7 @@ > >> > #define INTEL_PSTATE_SAMPLING_INTERVAL (10 * NSEC_PER_MSEC) > >> > > >> > #define INTEL_CPUFREQ_TRANSITION_LATENCY 20000 > >> > +#define INTEL_CPUFREQ_TRANSITION_DELAY_HWP 5000 > >> > #define INTEL_CPUFREQ_TRANSITION_DELAY 500 > >> > > >> > #ifdef CONFIG_ACPI > >> > @@ -95,6 +96,8 @@ static inline int32_t percent_ext_fp(int > >> > return div_ext_fp(percent, 100); > >> > } > >> > > >> > +#define HWP_EPP_TO_BYTE(x) (((u64)x >> 24) & 0xFF) > >> > + > >> > /** > >> > * struct sample - Store performance sample > >> > * @core_avg_perf: Ratio of APERF/MPERF which is the actual average > >> > @@ -2175,7 +2178,10 @@ static int intel_pstate_verify_policy(st > >> > > >> > static void intel_cpufreq_stop_cpu(struct cpufreq_policy *policy) > >> > { > >> > - intel_pstate_set_min_pstate(all_cpu_data[policy->cpu]); > >> > + if (hwp_active) > >> > + intel_pstate_hwp_force_min_perf(policy->cpu); > >> > + else > >> > + intel_pstate_set_min_pstate(all_cpu_data[policy->cpu]); > >> > } > >> > > >> > static void intel_pstate_stop_cpu(struct cpufreq_policy *policy) > >> > @@ -2183,12 +2189,10 @@ static void intel_pstate_stop_cpu(struct > >> > pr_debug("CPU %d exiting\n", policy->cpu); > >> > > >> > intel_pstate_clear_update_util_hook(policy->cpu); > >> > - if (hwp_active) { > >> > + if (hwp_active) > >> > intel_pstate_hwp_save_state(policy); > >> > - intel_pstate_hwp_force_min_perf(policy->cpu); > >> > - } else { > >> > - intel_cpufreq_stop_cpu(policy); > >> > - } > >> > + > >> > + intel_cpufreq_stop_cpu(policy); > >> > } > >> > > >> > static int intel_pstate_cpu_exit(struct cpufreq_policy *policy) > >> > @@ -2296,7 +2300,8 @@ static int intel_cpufreq_verify_policy(s > >> > #define INTEL_PSTATE_TRACE_TARGET 10 > >> > #define INTEL_PSTATE_TRACE_FAST_SWITCH 90 > >> > > >> > -static void intel_cpufreq_trace(struct cpudata *cpu, unsigned int trace_type, int old_pstate) > >> > +static void intel_cpufreq_trace(struct cpudata *cpu, unsigned int trace_type, > >> > + int from, int to) > >> > { > >> > struct sample *sample; > >> > > >> > @@ -2309,8 +2314,8 @@ static void intel_cpufreq_trace(struct c > >> > sample = &cpu->sample; > >> > trace_pstate_sample(trace_type, > >> > 0, > >> > - old_pstate, > >> > - cpu->pstate.current_pstate, > >> > + from, > >> > + to, > >> > sample->mperf, > >> > sample->aperf, > >> > sample->tsc, > >> > @@ -2318,40 +2323,110 @@ static void intel_cpufreq_trace(struct c > >> > fp_toint(cpu->iowait_boost * 100)); > >> > } > >> > > >> > -static int intel_cpufreq_target(struct cpufreq_policy *policy, > >> > - unsigned int target_freq, > >> > - unsigned int relation) > >> > +static void intel_cpufreq_update_hwp_request(struct cpudata *cpu, u8 new_epp) > >> > { > >> > - struct cpudata *cpu = all_cpu_data[policy->cpu]; > >> > - struct cpufreq_freqs freqs; > >> > - int target_pstate, old_pstate; > >> > + u64 value, prev; > >> > > >> > - update_turbo_state(); > >> > + prev = READ_ONCE(cpu->hwp_req_cached); > >> > + value = prev; > >> > > >> > - freqs.old = policy->cur; > >> > - freqs.new = target_freq; > >> > + /* > >> > + * The entire MSR needs to be updated in order to update the EPP field > >> > + * in it, so opportunistically update the min and max too if needed. > >> > + */ > >> > + value &= ~HWP_MIN_PERF(~0L); > >> > + value |= HWP_MIN_PERF(cpu->min_perf_ratio); > >> > + > >> > + value &= ~HWP_MAX_PERF(~0L); > >> > + value |= HWP_MAX_PERF(cpu->max_perf_ratio); > >> > + > >> > + if (boot_cpu_has(X86_FEATURE_HWP_EPP)) { > >> > + intel_cpufreq_trace(cpu, INTEL_PSTATE_TRACE_TARGET, > >> > + HWP_EPP_TO_BYTE(prev), new_epp); > >> > + > >> > + value &= ~GENMASK_ULL(31, 24); > >> > + value |= HWP_ENERGY_PERF_PREFERENCE(new_epp); > >> > + } > >> > + > >> > + if (value != prev) { > >> > + WRITE_ONCE(cpu->hwp_req_cached, value); > >> > + wrmsrl_on_cpu(cpu->cpu, MSR_HWP_REQUEST, value); > >> > + } > >> > +} > >> > + > >> > +/** > >> > + * intel_cpufreq_adjust_hwp_request - Adjust the HWP reuqest register. > >> > + * @cpu: Target CPU. > >> > + * @max_freq: Maximum frequency to consider. > >> > + * @target_freq: Target frequency selected by the governor. > >> > + * > >> > + * Translate the target frequency into a new EPP value to be written into the > >> > + * HWP request MSR of @cpu as a hint for the HW-driven P-state selection. > >> > + * > >> > + * The purpose of this is to avoid situations in which the kernel and the HWP > >> > + * algorithm work against each other by giving a hint about the expectations of > >> > + * the former to the latter. > >> > + * > >> > + * The mapping betweeen the target frequencies and the hint values need not be > >> > + * exact, but it must be monotonic, so that higher target frequencies always > >> > + * indicate more performance-oriented P-state selection. > >> > + */ > >> > +static void intel_cpufreq_adjust_hwp_request(struct cpudata *cpu, s64 max_freq, > >> > + unsigned int target_freq) > >> > +{ > >> > + s64 epp_fp = div_fp(255 * (max_freq - target_freq), max_freq); > >> > + > >> > + intel_cpufreq_update_hwp_request(cpu, fp_toint(epp_fp)); > >> > +} > >> > + > >> > >> Hey Rafael, I'm building a kernel with this in order to give it a try on > >> my system, but I'm skeptical that translating the target frequency to an > >> EPP value will work reliably. AFAIA the EPP value only has an indirect > >> influence on the processor's performance by adjusting the trade-off > >> between its responsiveness (rather than the actual clock frequency which > >> it will sustain in the long run) and its energy usage, in a largely > >> unspecified and non-linear way (non-linear like the effect of switching > >> CPU energy optimization features on and off, or like its effect on the > >> energy balancing behavior of the processor which can have a paradoxical > >> effect on performance). > >> > >> I doubt that the scheduling-based CPU utilization is a good predictor > >> for the optimal trade-off between those two variables. > > > > While I agree that this is not perfect, there barely is anything else > > that can be used for this purpose. > > > > Using the desired field or trying to adjust the limits relatively > > often would basically cause the P-state selection to be driven > > entirely by the kernel which simply doesn't know certain things only > > known to the P-unit, so it is reasonable to leave some level of > > control to the latter, so as to allow it to use the information known > > to it only. > > > > However, if it is allowed to do whatever it likes without any hints > > from the kernel, it may very well go against the scheduler's decisions > > which is not going to be optimal. > > > > I'm simply not sure if there is any other way to give such hints to it > > that through the EPP. > > > > Why not HWP_MIN_PERF? That would leave the HWP quite some room for > maneuvering (the whole HWP_MIN_PERF-HWP_MAX_PERF P-state range, it's not > like P-state selection would be entirely driven by the kernel), while > avoiding every failure scenario I was describing in my previous reply.
Actually, I have been thinking about the HWP min as an alternative that may be worth evaluating.
However, I would rather set the HWP min to something like 80% if the cpufreq request.
Let me cut an alternative patch.
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