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Commit 7bde2d50 authored by Srinivas Pandruvada's avatar Srinivas Pandruvada Committed by Rafael J. Wysocki
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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: default avatarSrinivas Pandruvada <srinivas.pandruvada@linux.intel.com>
[ rjw: Changelog ]
Signed-off-by: default avatarRafael J. Wysocki <rafael.j.wysocki@intel.com>
parent f5c13f44

drivers/cpufreq/intel_pstate.c

+10 −0
Original line number Original line Diff line number Diff line
@@ -1526,6 +1526,15 @@ static void intel_pstate_update_util(struct update_util_data *data, u64 time, 




	if (flags & SCHED_CPUFREQ_IOWAIT) {

	if (flags & SCHED_CPUFREQ_IOWAIT) {

		cpu->iowait_boost = int_tofp(1);

		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) {

	} else if (cpu->iowait_boost) {

		/* Clear iowait_boost if the CPU may have been idle. */

		/* Clear iowait_boost if the CPU may have been idle. */

		delta_ns = time - cpu->last_update;

		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)

	if ((s64)delta_ns < INTEL_PSTATE_DEFAULT_SAMPLING_INTERVAL)

		return;

		return;





set_pstate:

	if (intel_pstate_sample(cpu, time)) {

	if (intel_pstate_sample(cpu, time)) {

		int target_pstate;

		int target_pstate;