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authorSrinivas Pandruvada <srinivas.pandruvada@linux.intel.com>2017-08-03 19:03:14 -0700
committerRafael J. Wysocki <rafael.j.wysocki@intel.com>2017-08-04 13:58:57 +0200
commit7bde2d50014d3c5110b1db9a8e2659b6fa5f6b4a (patch)
tree326c079e22ca25a1d75572b99cebd229a9d82a43 /drivers/cpufreq
parentf5c13f44c7ad4fc0ce78e5da996762c2aebf510b (diff)
cpufreq: intel_pstate: Improve IO performance with per-core P-states
In the current implementation, the response latency between seeing SCHED_CPUFREQ_IOWAIT set and the actual P-state adjustment can be up to 10ms. It can be reduced by bumping up the P-state to the max at the time SCHED_CPUFREQ_IOWAIT is passed to intel_pstate_update_util(). With this change, the IO performance improves significantly. For a simple "grep -r . linux" (Here linux is the kernel source folder) with caches dropped every time on a Broadwell Xeon workstation with per-core P-states, the user and system time is shorter by as much as 30% - 40%. The same performance difference was not observed on clients that don't support per-core P-state. Signed-off-by: Srinivas Pandruvada <srinivas.pandruvada@linux.intel.com> [ rjw: Changelog ] Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Diffstat (limited to 'drivers/cpufreq')
-rw-r--r--drivers/cpufreq/intel_pstate.c10
1 files changed, 10 insertions, 0 deletions
diff --git a/drivers/cpufreq/intel_pstate.c b/drivers/cpufreq/intel_pstate.c
index 2eac2adff11b..532e261b2cab 100644
--- a/drivers/cpufreq/intel_pstate.c
+++ b/drivers/cpufreq/intel_pstate.c
@@ -1526,6 +1526,15 @@ static void intel_pstate_update_util(struct update_util_data *data, u64 time,
if (flags & SCHED_CPUFREQ_IOWAIT) {
cpu->iowait_boost = int_tofp(1);
+ cpu->last_update = time;
+ /*
+ * The last time the busy was 100% so P-state was max anyway
+ * so avoid overhead of computation.
+ */
+ if (fp_toint(cpu->sample.busy_scaled) == 100)
+ return;
+
+ goto set_pstate;
} else if (cpu->iowait_boost) {
/* Clear iowait_boost if the CPU may have been idle. */
delta_ns = time - cpu->last_update;
@@ -1537,6 +1546,7 @@ static void intel_pstate_update_util(struct update_util_data *data, u64 time,
if ((s64)delta_ns < INTEL_PSTATE_DEFAULT_SAMPLING_INTERVAL)
return;
+set_pstate:
if (intel_pstate_sample(cpu, time)) {
int target_pstate;