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SubjectRe: [RFC/RFT] [PATCH v2 4/6] cpufreq: intel_pstate: HWP boost performance on IO wakeup
On Thu, May 24, 2018 at 3:47 AM, Srinivas Pandruvada
<srinivas.pandruvada@linux.intel.com> wrote:
> This change uses SCHED_CPUFREQ_IOWAIT flag to boost HWP performance.
> Since SCHED_CPUFREQ_IOWAIT flag is set frequently, we don't start
> boosting steps unless we see two consecutive flags in two ticks. This
> avoids boosting due to IO because of regular system activities.
>
> To avoid synchronization issues, the actual processing of the flag is
> done on the local CPU callback.
>
> Signed-off-by: Srinivas Pandruvada <srinivas.pandruvada@linux.intel.com>
> ---
> drivers/cpufreq/intel_pstate.c | 44 ++++++++++++++++++++++++++++++++++++++++++
> 1 file changed, 44 insertions(+)
>
> diff --git a/drivers/cpufreq/intel_pstate.c b/drivers/cpufreq/intel_pstate.c
> index 382160570b5f..6d0ebe4fe1c7 100644
> --- a/drivers/cpufreq/intel_pstate.c
> +++ b/drivers/cpufreq/intel_pstate.c
> @@ -223,6 +223,8 @@ struct global_params {
> * operation
> * @hwp_req_cached: Cached value of the last HWP Request MSR
> * @hwp_cap_cached: Cached value of the last HWP Capabilities MSR
> + * @last_io_update: Last time when IO wake flag was set
> + * @sched_flags: Store scheduler flags for possible cross CPU update
> * @hwp_boost_min: Last HWP boosted min performance
> *
> * This structure stores per CPU instance data for all CPUs.
> @@ -258,6 +260,8 @@ struct cpudata {
> s16 epp_saved;
> u64 hwp_req_cached;
> u64 hwp_cap_cached;
> + u64 last_io_update;
> + unsigned long sched_flags;
> int hwp_boost_min;
> };
>
> @@ -1462,9 +1466,49 @@ static inline bool intel_pstate_hwp_boost_down(struct cpudata *cpu)
> return false;
> }
>
> +static inline void intel_pstate_update_util_hwp_local(struct cpudata *cpu,
> + u64 time)
> +{
> + bool io_flag;
> +
> + cpu->sample.time = time;
> + io_flag = test_and_clear_bit(SCHED_CPUFREQ_IOWAIT, &cpu->sched_flags);

I don't think you need to use bit ops here.

_update_util() runs under rq->lock for the target CPU, so it will not
run concurrently on two different CPUs for the same target anyway.

> + if (io_flag) {
> + bool do_io = false;
> +
> + /*
> + * Set iowait_boost flag and update time. Since IO WAIT flag
> + * is set all the time, we can't just conclude that there is
> + * some IO bound activity is scheduled on this CPU with just
> + * one occurrence. If we receive at least two in two
> + * consecutive ticks, then we treat as boost candidate.
> + */
> + if (time_before64(time, cpu->last_io_update + 2 * TICK_NSEC))
> + do_io = true;
> +
> + cpu->last_io_update = time;
> +
> + if (do_io)
> + intel_pstate_hwp_boost_up(cpu);

But what happens if user space wants to update the limits while
boosting is in effect? Shouldn't it take hwp_boost_min into account
then?

> +
> + } else {
> + if (intel_pstate_hwp_boost_down(cpu))
> + return;
> + }
> +
> + cpu->last_update = time;
> +}
> +
> static inline void intel_pstate_update_util_hwp(struct update_util_data *data,
> u64 time, unsigned int flags)
> {
> + struct cpudata *cpu = container_of(data, struct cpudata, update_util);
> +
> + if (flags & SCHED_CPUFREQ_IOWAIT)
> + set_bit(SCHED_CPUFREQ_IOWAIT, &cpu->sched_flags);
> +
> + if (smp_processor_id() == cpu->cpu)
> + intel_pstate_update_util_hwp_local(cpu, time);
> }
>
> static inline void intel_pstate_calc_avg_perf(struct cpudata *cpu)
> --
> 2.13.6
>

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