[PATCH] cpufreq: intel_pstate: Change the calculation of next pstate

[PATCH] cpufreq: intel_pstate: Change the calculation of next pstate

[Stratos Karafotis]

Currently the driver calculates the next pstate proportional to
core_busy factor and reverse proportional to current pstate.

Change the above method and calculate the next pstate independently
of current pstate.

Tested on Intel i7-3770 CPU @ 3.40GHz.
Phoronix benchmark of Linux Kernel Compilation 3.1 test shows an
increase ~1.5% in performance. Below the test results using turbostat
(5 iterations):

Without patch:

Ph. avg Time	Total time	PkgWatt		Total Energy
	79.63	266.416		57.74		15382.85984
	79.63	265.609		57.87		15370.79283
	79.57	266.994		57.54		15362.83476
	79.53	265.304		57.83		15342.53032
	79.71	265.977		57.76		15362.83152
avg	79.61	266.06		57.74		15364.36985

With patch:

Ph. avg Time	Total time	PkgWatt		Total Energy
	78.23	258.826		59.14		15306.96964
	78.41	259.110		59.15		15326.35650
	78.40	258.530		59.26		15320.48780
	78.46	258.673		59.20		15313.44160
	78.19	259.075		59.16		15326.87700
avg	78.34	258.842		59.18		15318.82650

The total test time reduced by ~2.6%, while the total energy
consumption during a test iteration reduced by ~0.35%

Signed-off-by: Stratos Karafotis <stratosk@semaphore.gr>
---
 drivers/cpufreq/intel_pstate.c | 15 +++++++--------
 1 file changed, 7 insertions(+), 8 deletions(-)

diff --git a/drivers/cpufreq/intel_pstate.c b/drivers/cpufreq/intel_pstate.c
index 0999673..8e309db 100644
--- a/drivers/cpufreq/intel_pstate.c
+++ b/drivers/cpufreq/intel_pstate.c
@@ -608,28 +608,27 @@ static inline void intel_pstate_set_sample_time(struct cpudata *cpu)
 	mod_timer_pinned(&cpu->timer, jiffies + delay);
 }
 
-static inline int32_t intel_pstate_get_scaled_busy(struct cpudata *cpu)
+static inline int32_t intel_pstate_get_busy(struct cpudata *cpu)
 {
-	int32_t core_busy, max_pstate, current_pstate;
+	int32_t core_busy, max_pstate;
 
 	core_busy = cpu->sample.core_pct_busy;
 	max_pstate = int_tofp(cpu->pstate.max_pstate);
-	current_pstate = int_tofp(cpu->pstate.current_pstate);
-	core_busy = mul_fp(core_busy, div_fp(max_pstate, current_pstate));
+	core_busy = mul_fp(core_busy, max_pstate);
 	return FP_ROUNDUP(core_busy);
 }
 
 static inline void intel_pstate_adjust_busy_pstate(struct cpudata *cpu)
 {
-	int32_t busy_scaled;
+	int32_t busy;
 	struct _pid *pid;
 	signed int ctl = 0;
 	int steps;
 
 	pid = &cpu->pid;
-	busy_scaled = intel_pstate_get_scaled_busy(cpu);
+	busy = intel_pstate_get_busy(cpu);
 
-	ctl = pid_calc(pid, busy_scaled);
+	ctl = pid_calc(pid, busy);
 
 	steps = abs(ctl);
 
@@ -651,7 +650,7 @@ static void intel_pstate_timer_func(unsigned long __data)
 	intel_pstate_adjust_busy_pstate(cpu);
 
 	trace_pstate_sample(fp_toint(sample->core_pct_busy),
-			fp_toint(intel_pstate_get_scaled_busy(cpu)),
+			fp_toint(intel_pstate_get_busy(cpu)),
 			cpu->pstate.current_pstate,
 			sample->mperf,
 			sample->aperf,
-- 
1.9.0

Re: [PATCH] cpufreq: intel_pstate: Change the calculation of next pstate

[Viresh Kumar]

Cc'd Dirk,

On 28 April 2014 03:42, Stratos Karafotis <stratosk@semaphore.gr> wrote:
> Currently the driver calculates the next pstate proportional to
> core_busy factor and reverse proportional to current pstate.
>
> Change the above method and calculate the next pstate independently
> of current pstate.

We must mention why the change is required.

Re: [PATCH] cpufreq: intel_pstate: Change the calculation of next pstate

[Stratos Karafotis]

On 29/04/2014 07:58 πμ, Viresh Kumar wrote:
> Cc'd Dirk,
> 
> On 28 April 2014 03:42, Stratos Karafotis <stratosk@semaphore.gr> wrote:
>> Currently the driver calculates the next pstate proportional to
>> core_busy factor and reverse proportional to current pstate.
>>
>> Change the above method and calculate the next pstate independently
>> of current pstate.
> 
> We must mention why the change is required.
> 

Hi Viresh,

Actually, I can't say that it's required. :)
I just believe that calculation of next p-state should be independent
from current one. In my opinion we can't scale the load across different
p-states, because it's not always equivalent.

For example suppose a load of 100% because of a tight for loop in the
current p-state. It will be also a 100% load in any other p-state.
It will be wrong if we scale the load in the calculation formula
according to the current p-state.

I included the test results in the change log to point out an improvement
because of this patch.

I will enrich more the change log as you suggested.

Thanks,
Stratos Karafotis

Re: [PATCH] cpufreq: intel_pstate: Change the calculation of next pstate

[Rafael J. Wysocki]

On Tuesday, April 29, 2014 07:34:46 PM Stratos Karafotis wrote:
> On 29/04/2014 07:58 πμ, Viresh Kumar wrote:
> > Cc'd Dirk,
> > 
> > On 28 April 2014 03:42, Stratos Karafotis <stratosk@semaphore.gr> wrote:
> >> Currently the driver calculates the next pstate proportional to
> >> core_busy factor and reverse proportional to current pstate.
> >>
> >> Change the above method and calculate the next pstate independently
> >> of current pstate.
> > 
> > We must mention why the change is required.
> > 
> 
> Hi Viresh,
> 
> Actually, I can't say that it's required. :)
> I just believe that calculation of next p-state should be independent
> from current one. In my opinion we can't scale the load across different
> p-states, because it's not always equivalent.
> 
> For example suppose a load of 100% because of a tight for loop in the
> current p-state. It will be also a 100% load in any other p-state.
> It will be wrong if we scale the load in the calculation formula
> according to the current p-state.
> 
> I included the test results in the change log to point out an improvement
> because of this patch.
> 
> I will enrich more the change log as you suggested.

Please do so.

Also, we need to take your patch to our power lab and see if we can reproduce
your results in other workloads.

And I'm waiting for the intel_pstate developer Dirk Brandewie to comment.

Thanks!

-- 
I speak only for myself.
Rafael J. Wysocki, Intel Open Source Technology Center.

Re: [PATCH] cpufreq: intel_pstate: Change the calculation of next pstate

[Dirk Brandewie]

On 04/29/2014 02:52 PM, Rafael J. Wysocki wrote:
> On Tuesday, April 29, 2014 07:34:46 PM Stratos Karafotis wrote:
>> On 29/04/2014 07:58 πμ, Viresh Kumar wrote:
>>> Cc'd Dirk,
>>>
>>> On 28 April 2014 03:42, Stratos Karafotis <stratosk@semaphore.gr> wrote:
>>>> Currently the driver calculates the next pstate proportional to
>>>> core_busy factor and reverse proportional to current pstate.
>>>>
>>>> Change the above method and calculate the next pstate independently
>>>> of current pstate.
>>>
>>> We must mention why the change is required.
>>>
>>
>> Hi Viresh,
>>
>> Actually, I can't say that it's required. :)
>> I just believe that calculation of next p-state should be independent
>> from current one. In my opinion we can't scale the load across different
>> p-states, because it's not always equivalent.
>>
>> For example suppose a load of 100% because of a tight for loop in the
>> current p-state. It will be also a 100% load in any other p-state.
>> It will be wrong if we scale the load in the calculation formula
>> according to the current p-state.
>>
>> I included the test results in the change log to point out an improvement
>> because of this patch.
>>
>> I will enrich more the change log as you suggested.
>
> Please do so.
>
> Also, we need to take your patch to our power lab and see if we can reproduce
> your results in other workloads.
>
> And I'm waiting for the intel_pstate developer Dirk Brandewie to comment.

Sorry I just returned from dealing with a family emergency and am digging
out of my inbox.

I will run this patch through some tests.


>
> Thanks!
>