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SubjectRe: [RFC/RFT] [PATCH v2 2/6] cpufreq: intel_pstate: Add HWP boost utility functions
On Thu, May 24, 2018 at 3:47 AM, Srinivas Pandruvada
<srinivas.pandruvada@linux.intel.com> wrote:
> Added two utility functions to HWP boost up gradually and boost down to
> the default cached HWP request values.
>
> Boost up:
> Boost up updates HWP request minimum value in steps. This minimum value
> can reach upto at HWP request maximum values depends on how frequently,
> the IOWAIT flag is set. At max, boost up will take three steps to reach
> the maximum, depending on the current HWP request levels and HWP
> capabilities. For example, if the current settings are:
> If P0 (Turbo max) = P1 (Guaranteed max) = min
> No boost at all.
> If P0 (Turbo max) > P1 (Guaranteed max) = min
> Should result in one level boost only for P0.
> If P0 (Turbo max) = P1 (Guaranteed max) > min
> Should result in two level boost:
> (min + p1)/2 and P1.
> If P0 (Turbo max) > P1 (Guaranteed max) > min
> Should result in three level boost:
> (min + p1)/2, P1 and P0.
> We don't set any level between P0 and P1 as there is no guarantee that
> they will be honored.
>
> Boost down:
> After the system is idle for hold time of 3ms, the HWP request is reset
> to the default cached value from HWP init or user modified one via sysfs.
>
> Signed-off-by: Srinivas Pandruvada <srinivas.pandruvada@linux.intel.com>
> ---
> drivers/cpufreq/intel_pstate.c | 74 ++++++++++++++++++++++++++++++++++++++++++
> 1 file changed, 74 insertions(+)
>
> diff --git a/drivers/cpufreq/intel_pstate.c b/drivers/cpufreq/intel_pstate.c
> index baed29c768e7..6ad46e07cad6 100644
> --- a/drivers/cpufreq/intel_pstate.c
> +++ b/drivers/cpufreq/intel_pstate.c
> @@ -223,6 +223,7 @@ 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
> + * @hwp_boost_min: Last HWP boosted min performance
> *
> * This structure stores per CPU instance data for all CPUs.
> */
> @@ -257,6 +258,7 @@ struct cpudata {
> s16 epp_saved;
> u64 hwp_req_cached;
> u64 hwp_cap_cached;
> + int hwp_boost_min;
> };
>
> static struct cpudata **all_cpu_data;
> @@ -1387,6 +1389,78 @@ static void intel_pstate_get_cpu_pstates(struct cpudata *cpu)
> intel_pstate_set_min_pstate(cpu);
> }
>
> +/*
> + * Long hold time will keep high perf limits for long time,
> + * which negatively impacts perf/watt for some workloads,
> + * like specpower. 3ms is based on experiements on some
> + * workoads.
> + */
> +static int hwp_boost_hold_time_ms = 3;
> +
> +static inline void intel_pstate_hwp_boost_up(struct cpudata *cpu)
> +{
> + u64 hwp_req = READ_ONCE(cpu->hwp_req_cached);

If user space updates the limits after this read, our decision below
may be based on a stale value, may it not?

> + int max_limit = (hwp_req & 0xff00) >> 8;
> + int min_limit = (hwp_req & 0xff);
> + int boost_level1;
> +
> + /*
> + * Cases to consider (User changes via sysfs or boot time):
> + * If, P0 (Turbo max) = P1 (Guaranteed max) = min:
> + * No boost, return.
> + * If, P0 (Turbo max) > P1 (Guaranteed max) = min:
> + * Should result in one level boost only for P0.
> + * If, P0 (Turbo max) = P1 (Guaranteed max) > min:
> + * Should result in two level boost:
> + * (min + p1)/2 and P1.
> + * If, P0 (Turbo max) > P1 (Guaranteed max) > min:
> + * Should result in three level boost:
> + * (min + p1)/2, P1 and P0.
> + */
> +
> + /* If max and min are equal or already at max, nothing to boost */
> + if (max_limit == min_limit || cpu->hwp_boost_min >= max_limit)
> + return;
> +
> + if (!cpu->hwp_boost_min)
> + cpu->hwp_boost_min = min_limit;
> +
> + /* level at half way mark between min and guranteed */
> + boost_level1 = (HWP_GUARANTEED_PERF(cpu->hwp_cap_cached) + min_limit) >> 1;
> +
> + if (cpu->hwp_boost_min < boost_level1)
> + cpu->hwp_boost_min = boost_level1;
> + else if (cpu->hwp_boost_min < HWP_GUARANTEED_PERF(cpu->hwp_cap_cached))
> + cpu->hwp_boost_min = HWP_GUARANTEED_PERF(cpu->hwp_cap_cached);
> + else if (cpu->hwp_boost_min == HWP_GUARANTEED_PERF(cpu->hwp_cap_cached) &&
> + max_limit != HWP_GUARANTEED_PERF(cpu->hwp_cap_cached))
> + cpu->hwp_boost_min = max_limit;
> + else
> + return;
> +
> + hwp_req = (hwp_req & ~GENMASK_ULL(7, 0)) | cpu->hwp_boost_min;
> + wrmsrl(MSR_HWP_REQUEST, hwp_req);
> + cpu->last_update = cpu->sample.time;
> +}
> +
> +static inline bool intel_pstate_hwp_boost_down(struct cpudata *cpu)
> +{
> + if (cpu->hwp_boost_min) {
> + bool expired;
> +
> + /* Check if we are idle for hold time to boost down */
> + expired = time_after64(cpu->sample.time, cpu->last_update +
> + (hwp_boost_hold_time_ms * NSEC_PER_MSEC));
> + if (expired) {
> + wrmsrl(MSR_HWP_REQUEST, cpu->hwp_req_cached);
> + cpu->hwp_boost_min = 0;
> + return true;
> + }
> + }
> +
> + return false;
> +}
> +
> static inline void intel_pstate_calc_avg_perf(struct cpudata *cpu)
> {
> struct sample *sample = &cpu->sample;
> --
> 2.13.6
>

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