[RFC/RFT] [PATCH v3 1/4] cpufreq: intel_pstate: Add HWP boost utility and sched util hooks

[Srinivas Pandruvada]

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,
this boost up function is called. 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 value from HWP init or user modified one via sysfs.

Caching of HWP Request and Capabilities
Store the HWP request value last set using MSR_HWP_REQUEST and read
MSR_HWP_CAPABILITIES. This avoid reading of MSRs in the boost utility
functions.

These boost utility functions calculated limits are based on the latest
HWP request value, which can be modified by setpolicy() callback. So if
user space modifies the minimum perf value, that will be accounted for
every time the boost up is called. There will be case when there can be
contention with the user modified minimum perf, in that case user value
will gain precedence. For example just before HWP_REQUEST MSR is updated
from setpolicy() callback, the boost up function is called via scheduler
tick callback. Here the cached MSR value is already the latest and limits
are updated based on the latest user limits, but on return the MSR write
callback called from setpolicy() callback will update the HWP_REQUEST
value. This will be used till next time the boost up function is called.

In addition add a variable to control HWP dynamic boosting. When HWP
dynamic boost is active then set the HWP specific update util hook. The
contents in the utility hooks will be filled in the subsequent patches.

Signed-off-by: Srinivas Pandruvada <srinivas.pandruvada@xxxxxxxxxxxxxxx>
---
 drivers/cpufreq/intel_pstate.c | 99 ++++++++++++++++++++++++++++++++++++++++--
 1 file changed, 95 insertions(+), 4 deletions(-)

diff --git a/drivers/cpufreq/intel_pstate.c b/drivers/cpufreq/intel_pstate.c
index 17e566afbb41..80bf61ae4b1f 100644
--- a/drivers/cpufreq/intel_pstate.c
+++ b/drivers/cpufreq/intel_pstate.c
@@ -221,6 +221,9 @@ struct global_params {
  *			preference/bias
  * @epp_saved:		Saved EPP/EPB during system suspend or CPU offline
  *			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.
  */
@@ -253,6 +256,9 @@ struct cpudata {
 	s16 epp_policy;
 	s16 epp_default;
 	s16 epp_saved;
+	u64 hwp_req_cached;
+	u64 hwp_cap_cached;
+	int hwp_boost_min;
 };
 
 static struct cpudata **all_cpu_data;
@@ -285,6 +291,7 @@ static struct pstate_funcs pstate_funcs __read_mostly;
 
 static int hwp_active __read_mostly;
 static bool per_cpu_limits __read_mostly;
+static bool hwp_boost __read_mostly;
 
 static struct cpufreq_driver *intel_pstate_driver __read_mostly;
 
@@ -689,6 +696,7 @@ static void intel_pstate_get_hwp_max(unsigned int cpu, int *phy_max,
 	u64 cap;
 
 	rdmsrl_on_cpu(cpu, MSR_HWP_CAPABILITIES, &cap);
+	WRITE_ONCE(all_cpu_data[cpu]->hwp_cap_cached, cap);
 	if (global.no_turbo)
 		*current_max = HWP_GUARANTEED_PERF(cap);
 	else
@@ -763,6 +771,7 @@ static void intel_pstate_hwp_set(unsigned int cpu)
 		intel_pstate_set_epb(cpu, epp);
 	}
 skip_epp:
+	WRITE_ONCE(cpu_data->hwp_req_cached, value);
 	wrmsrl_on_cpu(cpu, MSR_HWP_REQUEST, value);
 }
 
@@ -1381,6 +1390,81 @@ 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 void 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;
+		}
+	}
+	cpu->last_update = cpu->sample.time;
+}
+
+static inline void intel_pstate_update_util_hwp(struct update_util_data *data,
+						u64 time, unsigned int flags)
+{
+}
+
 static inline void intel_pstate_calc_avg_perf(struct cpudata *cpu)
 {
 	struct sample *sample = &cpu->sample;
@@ -1684,7 +1768,7 @@ static void intel_pstate_set_update_util_hook(unsigned int cpu_num)
 {
 	struct cpudata *cpu = all_cpu_data[cpu_num];
 
-	if (hwp_active)
+	if (hwp_active && !hwp_boost)
 		return;
 
 	if (cpu->update_util_set)
@@ -1692,8 +1776,12 @@ static void intel_pstate_set_update_util_hook(unsigned int cpu_num)
 
 	/* Prevent intel_pstate_update_util() from using stale data. */
 	cpu->sample.time = 0;
-	cpufreq_add_update_util_hook(cpu_num, &cpu->update_util,
-				     intel_pstate_update_util);
+	if (hwp_active)
+		cpufreq_add_update_util_hook(cpu_num, &cpu->update_util,
+					     intel_pstate_update_util_hwp);
+	else
+		cpufreq_add_update_util_hook(cpu_num, &cpu->update_util,
+					     intel_pstate_update_util);
 	cpu->update_util_set = true;
 }
 
@@ -1805,8 +1893,11 @@ static int intel_pstate_set_policy(struct cpufreq_policy *policy)
 		intel_pstate_set_update_util_hook(policy->cpu);
 	}
 
-	if (hwp_active)
+	if (hwp_active) {
+		if (!hwp_boost)
+			intel_pstate_clear_update_util_hook(policy->cpu);
 		intel_pstate_hwp_set(policy->cpu);
+	}
 
 	mutex_unlock(&intel_pstate_limits_lock);
 
-- 
2.13.6