Re: [PATCH 07/10] cpufreq: intel_pstate: Implement VLP controller for HWP parts.

[Francisco Jerez <currojerez@riseup.net>]

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"Pandruvada, Srinivas" <srinivas.pandruvada@intel.com> writes:

> On Wed, 2020-03-18 at 12:51 -0700, Francisco Jerez wrote:
>> "Pandruvada, Srinivas" <srinivas.pandruvada@intel.com> writes:
>> 
>> > On Tue, 2020-03-10 at 14:42 -0700, Francisco Jerez wrote:
>> > > This implements a simple variably low-pass-filtering governor in
>> > > control of the HWP MIN/MAX PERF range based on the previously
>> > > introduced get_vlp_target_range().  See "cpufreq: intel_pstate:
>> > > Implement VLP controller target P-state range estimation." for
>> > > the
>> > > rationale.
>> > 
>> > I just gave a try on a pretty idle system with just systemd
>> > processes
>> > and usual background tasks with nomodset. 
>> > 
>> > I see that there HWP min is getting changed between 4-8. Why are
>> > changing HWP dynamic range even on an idle system running no where
>> > close to TDP?
>> > 
>> 
>> The HWP request range is clamped to the frequency range specified by
>> the
>> CPUFREQ policy and to the cpu->pstate.min_pstate bound.
>> 
>> If you see the HWP minimum fluctuating above that it's likely a sign
>> of
>> your system not being completely idle -- If that's the case it's
>> likely
>> to go away after you do:
>> 
>>  echo 0 > /sys/kernel/debug/pstate_snb/vlp_realtime_gain_pml
>> 
> The objective which I though was to improve performance of GPU
> workloads limited by TDP because of P-states ramping up and resulting
> in less power to GPU to complete a task.
>  
> HWP takes decision not on just load on a CPU but several other factors
> like total SoC power and scalability. We don't want to disturb HWP
> algorithms when there is no TDP limitations. If writing 0, causes this
> behavior then that should be the default.
>

The heuristic disabled by that debugfs file is there to avoid
regressions in latency-sensitive workloads as you can probably get from
the ecomments.  However ISTR those regressions were specific to non-HWP
systems, so I wouldn't mind disabling it for the moment (or punting it
to the non-HWP series if you like)j.  But first I need to verify that
there are no performance regressions on HWP systems after changing that.
Can you confirm that the debugfs write above prevents the behavior you'd
like to avoid?

> Thanks,
> Srinivas
>
>
>
>
>
>> > Thanks,
>> > Srinivas
>> > 
>> > 
>> > > Signed-off-by: Francisco Jerez <currojerez@riseup.net>
>> > > ---
>> > >  drivers/cpufreq/intel_pstate.c | 79
>> > > +++++++++++++++++++++++++++++++++-
>> > >  1 file changed, 77 insertions(+), 2 deletions(-)
>> > > 
>> > > diff --git a/drivers/cpufreq/intel_pstate.c
>> > > b/drivers/cpufreq/intel_pstate.c
>> > > index cecadfec8bc1..a01eed40d897 100644
>> > > --- a/drivers/cpufreq/intel_pstate.c
>> > > +++ b/drivers/cpufreq/intel_pstate.c
>> > > @@ -1905,6 +1905,20 @@ static void intel_pstate_reset_vlp(struct
>> > > cpudata *cpu)
>> > >  	vlp->gain = max(1, div_fp(1000, vlp_params.setpoint_0_pml));
>> > >  	vlp->target.p_base = 0;
>> > >  	vlp->stats.last_response_frequency_hz = vlp_params.avg_hz;
>> > > +
>> > > +	if (hwp_active) {
>> > > +		const uint32_t p0 = max(cpu->pstate.min_pstate,
>> > > +					cpu->min_perf_ratio);
>> > > +		const uint32_t p1 = max_t(uint32_t, p0, cpu-
>> > > > max_perf_ratio);
>> > > +		const uint64_t hwp_req = (READ_ONCE(cpu-
>> > > > hwp_req_cached) &
>> > > +					  ~(HWP_MAX_PERF(~0L) |
>> > > +					    HWP_MIN_PERF(~0L) |
>> > > +					    HWP_DESIRED_PERF(~0L))) |
>> > > +					 HWP_MIN_PERF(p0) |
>> > > HWP_MAX_PERF(p1);
>> > > +
>> > > +		wrmsrl_on_cpu(cpu->cpu, MSR_HWP_REQUEST, hwp_req);
>> > > +		cpu->hwp_req_cached = hwp_req;
>> > > +	}
>> > >  }
>> > >  
>> > >  /**
>> > > @@ -2222,6 +2236,46 @@ static void
>> > > intel_pstate_adjust_pstate(struct
>> > > cpudata *cpu)
>> > >  		fp_toint(cpu->iowait_boost * 100));
>> > >  }
>> > >  
>> > > +static void intel_pstate_adjust_pstate_range(struct cpudata
>> > > *cpu,
>> > > +					     const unsigned int
>> > > range[])
>> > > +{
>> > > +	const int from = cpu->hwp_req_cached;
>> > > +	unsigned int p0, p1, p_min, p_max;
>> > > +	struct sample *sample;
>> > > +	uint64_t hwp_req;
>> > > +
>> > > +	update_turbo_state();
>> > > +
>> > > +	p0 = max(cpu->pstate.min_pstate, cpu->min_perf_ratio);
>> > > +	p1 = max_t(unsigned int, p0, cpu->max_perf_ratio);
>> > > +	p_min = clamp_t(unsigned int, range[0], p0, p1);
>> > > +	p_max = clamp_t(unsigned int, range[1], p0, p1);
>> > > +
>> > > +	trace_cpu_frequency(p_max * cpu->pstate.scaling, cpu->cpu);
>> > > +
>> > > +	hwp_req = (READ_ONCE(cpu->hwp_req_cached) &
>> > > +		   ~(HWP_MAX_PERF(~0L) | HWP_MIN_PERF(~0L) |
>> > > +		     HWP_DESIRED_PERF(~0L))) |
>> > > +		  HWP_MIN_PERF(vlp_params.debug & 2 ? p0 : p_min) |
>> > > +		  HWP_MAX_PERF(vlp_params.debug & 4 ? p1 : p_max);
>> > > +
>> > > +	if (hwp_req != cpu->hwp_req_cached) {
>> > > +		wrmsrl(MSR_HWP_REQUEST, hwp_req);
>> > > +		cpu->hwp_req_cached = hwp_req;
>> > > +	}
>> > > +
>> > > +	sample = &cpu->sample;
>> > > +	trace_pstate_sample(mul_ext_fp(100, sample->core_avg_perf),
>> > > +			    fp_toint(sample->busy_scaled),
>> > > +			    from,
>> > > +			    hwp_req,
>> > > +			    sample->mperf,
>> > > +			    sample->aperf,
>> > > +			    sample->tsc,
>> > > +			    get_avg_frequency(cpu),
>> > > +			    fp_toint(cpu->iowait_boost * 100));
>> > > +}
>> > > +
>> > >  static void intel_pstate_update_util(struct update_util_data
>> > > *data,
>> > > u64 time,
>> > >  				     unsigned int flags)
>> > >  {
>> > > @@ -2260,6 +2314,22 @@ static void
>> > > intel_pstate_update_util(struct
>> > > update_util_data *data, u64 time,
>> > >  		intel_pstate_adjust_pstate(cpu);
>> > >  }
>> > >  
>> > > +/**
>> > > + * Implementation of the cpufreq update_util hook based on the
>> > > VLP
>> > > + * controller (see get_vlp_target_range()).
>> > > + */
>> > > +static void intel_pstate_update_util_hwp_vlp(struct
>> > > update_util_data
>> > > *data,
>> > > +					     u64 time, unsigned int
>> > > flags)
>> > > +{
>> > > +	struct cpudata *cpu = container_of(data, struct cpudata,
>> > > update_util);
>> > > +
>> > > +	if (update_vlp_sample(cpu, time, flags)) {
>> > > +		const struct vlp_target_range *target =
>> > > +			get_vlp_target_range(cpu);
>> > > +		intel_pstate_adjust_pstate_range(cpu, target->value);
>> > > +	}
>> > > +}
>> > > +
>> > >  static struct pstate_funcs core_funcs = {
>> > >  	.get_max = core_get_max_pstate,
>> > >  	.get_max_physical = core_get_max_pstate_physical,
>> > > @@ -2389,6 +2459,9 @@ static int intel_pstate_init_cpu(unsigned
>> > > int
>> > > cpunum)
>> > >  
>> > >  	intel_pstate_get_cpu_pstates(cpu);
>> > >  
>> > > +	if (pstate_funcs.update_util ==
>> > > intel_pstate_update_util_hwp_vlp)
>> > > +		intel_pstate_reset_vlp(cpu);
>> > > +
>> > >  	pr_debug("controlling: cpu %d\n", cpunum);
>> > >  
>> > >  	return 0;
>> > > @@ -2398,7 +2471,8 @@ static void
>> > > intel_pstate_set_update_util_hook(unsigned int cpu_num)
>> > >  {
>> > >  	struct cpudata *cpu = all_cpu_data[cpu_num];
>> > >  
>> > > -	if (hwp_active && !hwp_boost)
>> > > +	if (hwp_active && !hwp_boost &&
>> > > +	    pstate_funcs.update_util !=
>> > > intel_pstate_update_util_hwp_vlp)
>> > >  		return;
>> > >  
>> > >  	if (cpu->update_util_set)
>> > > @@ -2526,7 +2600,8 @@ static int intel_pstate_set_policy(struct
>> > > cpufreq_policy *policy)
>> > >  		 * was turned off, in that case we need to clear the
>> > >  		 * update util hook.
>> > >  		 */
>> > > -		if (!hwp_boost)
>> > > +		if (!hwp_boost && pstate_funcs.update_util !=
>> > > +				  intel_pstate_update_util_hwp_vlp)
>> > >  			intel_pstate_clear_update_util_hook(policy-
>> > > > cpu);
>> > >  		intel_pstate_hwp_set(policy->cpu);
>> > >  	}

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