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Subject[RFC/RFT] [PATCH v2 2/6] cpufreq: intel_pstate: Add HWP boost utility functions
Date
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);
+ 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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