* [PATCH] cpufreq: intel_pstate: Improve IO performance
@ 2017-08-02 3:45 Srinivas Pandruvada
2017-08-04 0:34 ` Rafael J. Wysocki
0 siblings, 1 reply; 3+ messages in thread
From: Srinivas Pandruvada @ 2017-08-02 3:45 UTC (permalink / raw)
To: rjw, lenb; +Cc: linux-pm, Srinivas Pandruvada
In the current implementation the latency from SCHED_CPUFREQ_IOWAIT is
set to actual P-state adjustment can be upto 10ms. This can be improved
by reacting to SCHED_CPUFREQ_IOWAIT by jumping to max P-state immediately
. With this change the IO performance improves significantly.
With a simple "grep -r . linux" (Here linux is kernel source folder) with
dropped caches every time on a platform with per core P-states on a
Broadwell Xeon workstation, the user and system time improves as much as
30% to 40%.
The same performance difference was not observed on clients, which don't
have per core P-state support.
Signed-off-by: Srinivas Pandruvada <srinivas.pandruvada@linux.intel.com>
---
drivers/cpufreq/intel_pstate.c | 10 ++++++++++
1 file changed, 10 insertions(+)
diff --git a/drivers/cpufreq/intel_pstate.c b/drivers/cpufreq/intel_pstate.c
index 8c67b77..7762255 100644
--- a/drivers/cpufreq/intel_pstate.c
+++ b/drivers/cpufreq/intel_pstate.c
@@ -1527,6 +1527,15 @@ static void intel_pstate_update_util(struct update_util_data *data, u64 time,
if (flags & SCHED_CPUFREQ_IOWAIT) {
cpu->iowait_boost = int_tofp(1);
+ /*
+ * 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) {
+ cpu->last_update = time;
+ 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;
@@ -1538,6 +1547,7 @@ 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;
--
2.7.4
^ permalink raw reply related [flat|nested] 3+ messages in thread
* Re: [PATCH] cpufreq: intel_pstate: Improve IO performance
2017-08-02 3:45 [PATCH] cpufreq: intel_pstate: Improve IO performance Srinivas Pandruvada
@ 2017-08-04 0:34 ` Rafael J. Wysocki
2017-08-04 1:47 ` Srinivas Pandruvada
0 siblings, 1 reply; 3+ messages in thread
From: Rafael J. Wysocki @ 2017-08-04 0:34 UTC (permalink / raw)
To: Srinivas Pandruvada; +Cc: Rafael J. Wysocki, Len Brown, Linux PM
On Wed, Aug 2, 2017 at 5:45 AM, Srinivas Pandruvada
<srinivas.pandruvada@linux.intel.com> wrote:
> In the current implementation the latency from SCHED_CPUFREQ_IOWAIT is
> set to actual P-state adjustment can be upto 10ms. This can be improved
> by reacting to SCHED_CPUFREQ_IOWAIT by jumping to max P-state immediately
> . With this change the IO performance improves significantly.
>
> With a simple "grep -r . linux" (Here linux is kernel source folder) with
> dropped caches every time on a platform with per core P-states on a
> Broadwell Xeon workstation, the user and system time improves as much as
> 30% to 40%.
>
> The same performance difference was not observed on clients, which don't
> have per core P-state support.
>
> Signed-off-by: Srinivas Pandruvada <srinivas.pandruvada@linux.intel.com>
> ---
> drivers/cpufreq/intel_pstate.c | 10 ++++++++++
> 1 file changed, 10 insertions(+)
>
> diff --git a/drivers/cpufreq/intel_pstate.c b/drivers/cpufreq/intel_pstate.c
> index 8c67b77..7762255 100644
> --- a/drivers/cpufreq/intel_pstate.c
> +++ b/drivers/cpufreq/intel_pstate.c
> @@ -1527,6 +1527,15 @@ static void intel_pstate_update_util(struct update_util_data *data, u64 time,
>
> if (flags & SCHED_CPUFREQ_IOWAIT) {
> cpu->iowait_boost = int_tofp(1);
> + /*
> + * 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) {
> + cpu->last_update = time;
> + return;
> + }
> + goto set_pstate;
cpu->last_update should also be updated when you jump to set_pstate,
shouldn't it?
> } else if (cpu->iowait_boost) {
> /* Clear iowait_boost if the CPU may have been idle. */
> delta_ns = time - cpu->last_update;
> @@ -1538,6 +1547,7 @@ 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;
>
> --
> 2.7.4
>
^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: [PATCH] cpufreq: intel_pstate: Improve IO performance
2017-08-04 0:34 ` Rafael J. Wysocki
@ 2017-08-04 1:47 ` Srinivas Pandruvada
0 siblings, 0 replies; 3+ messages in thread
From: Srinivas Pandruvada @ 2017-08-04 1:47 UTC (permalink / raw)
To: Rafael J. Wysocki; +Cc: Rafael J. Wysocki, Len Brown, Linux PM
On Fri, 2017-08-04 at 02:34 +0200, Rafael J. Wysocki wrote:
> On Wed, Aug 2, 2017 at 5:45 AM, Srinivas Pandruvada
> <srinivas.pandruvada@linux.intel.com> wrote:
> >
> > In the current implementation the latency from SCHED_CPUFREQ_IOWAIT
> > is
> > set to actual P-state adjustment can be upto 10ms. This can be
> > improved
> > by reacting to SCHED_CPUFREQ_IOWAIT by jumping to max P-state
> > immediately
> > . With this change the IO performance improves significantly.
> >
> > With a simple "grep -r . linux" (Here linux is kernel source
> > folder) with
> > dropped caches every time on a platform with per core P-states on a
> > Broadwell Xeon workstation, the user and system time improves as
> > much as
> > 30% to 40%.
> >
> > The same performance difference was not observed on clients, which
> > don't
> > have per core P-state support.
> >
> > Signed-off-by: Srinivas Pandruvada <srinivas.pandruvada@linux.intel
> > .com>
> > ---
> > drivers/cpufreq/intel_pstate.c | 10 ++++++++++
> > 1 file changed, 10 insertions(+)
> >
> > diff --git a/drivers/cpufreq/intel_pstate.c
> > b/drivers/cpufreq/intel_pstate.c
> > index 8c67b77..7762255 100644
> > --- a/drivers/cpufreq/intel_pstate.c
> > +++ b/drivers/cpufreq/intel_pstate.c
> > @@ -1527,6 +1527,15 @@ static void intel_pstate_update_util(struct
> > update_util_data *data, u64 time,
> >
> > if (flags & SCHED_CPUFREQ_IOWAIT) {
> > cpu->iowait_boost = int_tofp(1);
> > + /*
> > + * 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) {
> > + cpu->last_update = time;
> > + return;
> > + }
> > + goto set_pstate;
> cpu->last_update should also be updated when you jump to set_pstate,
> shouldn't it?
Yes. It should be updated.
Thanks,
Srinivas
>
> >
> > } else if (cpu->iowait_boost) {
> > /* Clear iowait_boost if the CPU may have been
> > idle. */
> > delta_ns = time - cpu->last_update;
> > @@ -1538,6 +1547,7 @@ 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;
> >
> > --
> > 2.7.4
> >
^ permalink raw reply [flat|nested] 3+ messages in thread
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2017-08-02 3:45 [PATCH] cpufreq: intel_pstate: Improve IO performance Srinivas Pandruvada
2017-08-04 0:34 ` Rafael J. Wysocki
2017-08-04 1:47 ` Srinivas Pandruvada
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