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

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Message-ID: <3708753.N4DSO893cq@aspire.rjw.lan>
Date:   Sun, 13 May 2018 10:43:51 +0200
From:   "Rafael J. Wysocki" <rjw@...ysocki.net>
To:     Doug Smythies <doug.smythies@...il.com>,
        srinivas.pandruvada@...ux.intel.com
Cc:     dsmythies@...us.net, linux-kernel@...r.kernel.org,
        linux-pm@...r.kernel.org
Subject: Re: [PATCH V5] cpufreq: intel_pstate: allow trace in passive mode

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@...us.net>

Srinivas, any comments or concerns?

> 
> ---
> 
> 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;
> +	if (!intel_pstate_sample(cpu, ktime_get()))
> +		return;
> +	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;
>  }
>  
>