Re: [PATCH V5] cpufreq: intel_pstate: allow trace in passive mode

[Srinivas Pandruvada]

On Sun, 2018-05-13 at 10:43 +0200, Rafael J. Wysocki wrote:
> On Thursday, May 3, 2018 8:22:47 AM CEST Doug Smythies wrote:
> > Allow use of the trace_pstate_sample trace function
> > when the intel_pstate driver is in passive mode.
> > Since the core_busy and scaled_busy fields are not
> > used, and it might be desirable to know which path
> > through the driver was used, either intel_cpufreq_target
> > or intel_cpufreq_fast_switch, re-task the core_busy
> > field as a flag indicator.
> > 
> > The user can then use the intel_pstate_tracer.py utility
> > to summarize and plot the trace.
> > 
> > Note: The core_busy feild still goes by that name
> > in include/trace/events/power.h and within the
> > intel_pstate_tracer.py script and csv file headers,
> > but it is graphed as "performance", and called
> > core_avg_perf now in the intel_pstate driver.
> > 
> > Sometimes, in passive mode, the driver is not called for
> > many tens or even hundreds of seconds. The user
> > needs to understand, and not be confused by, this limitation.
> > 
> > Signed-off-by: Doug Smythies <dsmythies@xxxxxxxxx>
> 
> Srinivas, any comments or concerns?
> 
Looks fine. But as rest of code, prefer a newline after return.
So I am sending V6 version only with that change.

Thanks,
Srinivas
> > 
> > ---
> > 
> > V5: Changes as per Rafael J. Wysocki feedback.
> >     See: https://lkml.org/lkml/2018/1/7/270
> > 
> > V4: Only execute the trace specific overhead code if trace
> >     is enabled. Suggested by Srinivas Pandruvada.
> > 
> > V3: Move largely duplicate code to a subroutine.
> >     Suggested by Rafael J. Wysocki.
> > 
> > V2: prepare for resend. Rebase to current kernel, 4.15-rc3.
> > 
> > ---
> >  drivers/cpufreq/intel_pstate.c | 44
> > ++++++++++++++++++++++++++++++++++++++++--
> >  1 file changed, 42 insertions(+), 2 deletions(-)
> > 
> > diff --git a/drivers/cpufreq/intel_pstate.c
> > b/drivers/cpufreq/intel_pstate.c
> > index 17e566af..4a08686 100644
> > --- a/drivers/cpufreq/intel_pstate.c
> > +++ b/drivers/cpufreq/intel_pstate.c
> > @@ -1939,13 +1939,49 @@ static int
> > intel_cpufreq_verify_policy(struct cpufreq_policy *policy)
> >  	return 0;
> >  }
> >  
> > +/* Use of trace in passive mode:
> > + *
> > + * In passive mode the trace core_busy field (also known as the
> > + * performance field, and lablelled as such on the graphs; also
> > known as
> > + * core_avg_perf) is not needed and so is re-assigned to indicate
> > if the
> > + * driver call was via the normal or fast switch path. Various
> > graphs
> > + * output from the intel_pstate_tracer.py utility that include
> > core_busy
> > + * (or performance or core_avg_perf) have a fixed y-axis from 0 to
> > 100%,
> > + * so we use 10 to indicate the the normal path through the
> > driver, and
> > + * 90 to indicate the fast switch path through the driver.
> > + * The scaled_busy field is not used, and is set to 0.
> > + */
> > +
> > +#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)
> > +{
> > +	struct sample *sample;
> > +
> > +	if (!trace_pstate_sample_enabled())
> > +		return;
one newline

> > +	if (!intel_pstate_sample(cpu, ktime_get()))
> > +		return;
one new line

> > +	sample = &cpu->sample;
> > +	trace_pstate_sample(trace_type,
> > +		0,
> > +		old_pstate,
> > +		cpu->pstate.current_pstate,
> > +		sample->mperf,
> > +		sample->aperf,
> > +		sample->tsc,
> > +		get_avg_frequency(cpu),
> > +		fp_toint(cpu->iowait_boost * 100));
> > +}
> > +
> >  static int intel_cpufreq_target(struct cpufreq_policy *policy,
> >  				unsigned int target_freq,
> >  				unsigned int relation)
> >  {
> >  	struct cpudata *cpu = all_cpu_data[policy->cpu];
> >  	struct cpufreq_freqs freqs;
> > -	int target_pstate;
> > +	int target_pstate, old_pstate;
> >  
> >  	update_turbo_state();
> >  
> > @@ -1965,12 +2001,14 @@ static int intel_cpufreq_target(struct
> > cpufreq_policy *policy,
> >  		break;
> >  	}
> >  	target_pstate = intel_pstate_prepare_request(cpu,
> > target_pstate);
> > +	old_pstate = cpu->pstate.current_pstate;
> >  	if (target_pstate != cpu->pstate.current_pstate) {
> >  		cpu->pstate.current_pstate = target_pstate;
> >  		wrmsrl_on_cpu(policy->cpu, MSR_IA32_PERF_CTL,
> >  			      pstate_funcs.get_val(cpu,
> > target_pstate));
> >  	}
> >  	freqs.new = target_pstate * cpu->pstate.scaling;
> > +	intel_cpufreq_trace(cpu, INTEL_PSTATE_TRACE_TARGET,
> > old_pstate);
> >  	cpufreq_freq_transition_end(policy, &freqs, false);
> >  
> >  	return 0;
> > @@ -1980,13 +2018,15 @@ static unsigned int
> > intel_cpufreq_fast_switch(struct cpufreq_policy *policy,
> >  					      unsigned int
> > target_freq)
> >  {
> >  	struct cpudata *cpu = all_cpu_data[policy->cpu];
> > -	int target_pstate;
> > +	int target_pstate, old_pstate;
> >  
> >  	update_turbo_state();
> >  
> >  	target_pstate = DIV_ROUND_UP(target_freq, cpu-
> > >pstate.scaling);
> >  	target_pstate = intel_pstate_prepare_request(cpu,
> > target_pstate);
> > +	old_pstate = cpu->pstate.current_pstate;
> >  	intel_pstate_update_pstate(cpu, target_pstate);
> > +	intel_cpufreq_trace(cpu, INTEL_PSTATE_TRACE_FAST_SWITCH,
> > old_pstate);
> >  	return target_pstate * cpu->pstate.scaling;
> >  }
> >  
> > 
> 
>