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SubjectRe: [PATCH V5] cpufreq: intel_pstate: allow trace in passive mode
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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@telus.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;
> }
>
>


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