Re: [PATCH v5] cpuidle: Fix last_residency division
On Mon, Jul 4, 2016 at 8:10 AM, Balbir Singh wrote:
>
>
> On 02/07/16 00:24, Shreyas B. Prabhu wrote:
>> Snooze is a poll idle state in powernv and pseries platforms. Snooze
>> has a timeout so that if a cpu stays in snooze for more than target
>> residency of the next available idle state, then it would exit thereby
>> giving chance to the cpuidle governor to re-evaluate and
>> promote the cpu to a deeper idle state. Therefore whenever snooze exits
>> due to this timeout, its last_residency will be target_residency of next
>> deeper state.
>>
>> commit e93e59ce5b85 ("cpuidle: Replace ktime_get() with local_clock()")
>> changed the math around last_residency calculation. Specifically, while
>> converting last_residency value from nanoseconds to microseconds it does
>> right shift by 10. Due to this, in snooze timeout exit scenarios
>> last_residency calculated is roughly 2.3% less than target_residency of
>> next available state. This pattern is picked up get_typical_interval()
>> in the menu governor and therefore expected_interval in menu_select() is
>> frequently less than the target_residency of any state but snooze.
>>
>> Due to this we are entering snooze at a higher rate, thereby affecting
>> the single thread performance.
>>
>> Fix this by using precise division via ktime_us_delta.
>>
>> Reported-by: Anton Blanchard
>> Bisected-by: Shilpasri G Bhat
>> Signed-off-by: Shreyas B. Prabhu
>> ---
>
> This looks so much cleaner :)
>
> Acked-by: Balbir Singh
Patch applied, thanks!
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Re: [PATCH v5] cpuidle: Fix last_residency division
On 02/07/16 00:24, Shreyas B. Prabhu wrote:
> Snooze is a poll idle state in powernv and pseries platforms. Snooze
> has a timeout so that if a cpu stays in snooze for more than target
> residency of the next available idle state, then it would exit thereby
> giving chance to the cpuidle governor to re-evaluate and
> promote the cpu to a deeper idle state. Therefore whenever snooze exits
> due to this timeout, its last_residency will be target_residency of next
> deeper state.
>
> commit e93e59ce5b85 ("cpuidle: Replace ktime_get() with local_clock()")
> changed the math around last_residency calculation. Specifically, while
> converting last_residency value from nanoseconds to microseconds it does
> right shift by 10. Due to this, in snooze timeout exit scenarios
> last_residency calculated is roughly 2.3% less than target_residency of
> next available state. This pattern is picked up get_typical_interval()
> in the menu governor and therefore expected_interval in menu_select() is
> frequently less than the target_residency of any state but snooze.
>
> Due to this we are entering snooze at a higher rate, thereby affecting
> the single thread performance.
>
> Fix this by using precise division via ktime_us_delta.
>
> Reported-by: Anton Blanchard
> Bisected-by: Shilpasri G Bhat
> Signed-off-by: Shreyas B. Prabhu
> ---
This looks so much cleaner :)
Acked-by: Balbir Singh
Balbir
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Re: [PATCH v5] cpuidle: Fix last_residency division
On 07/01/2016 04:24 PM, Shreyas B. Prabhu wrote:
Snooze is a poll idle state in powernv and pseries platforms. Snooze
has a timeout so that if a cpu stays in snooze for more than target
residency of the next available idle state, then it would exit thereby
giving chance to the cpuidle governor to re-evaluate and
promote the cpu to a deeper idle state. Therefore whenever snooze exits
due to this timeout, its last_residency will be target_residency of next
deeper state.
commit e93e59ce5b85 ("cpuidle: Replace ktime_get() with local_clock()")
changed the math around last_residency calculation. Specifically, while
converting last_residency value from nanoseconds to microseconds it does
right shift by 10. Due to this, in snooze timeout exit scenarios
last_residency calculated is roughly 2.3% less than target_residency of
next available state. This pattern is picked up get_typical_interval()
in the menu governor and therefore expected_interval in menu_select() is
frequently less than the target_residency of any state but snooze.
Due to this we are entering snooze at a higher rate, thereby affecting
the single thread performance.
Fix this by using precise division via ktime_us_delta.
Reported-by: Anton Blanchard
Bisected-by: Shilpasri G Bhat
Signed-off-by: Shreyas B. Prabhu
---
Acked-by: Daniel Lezcano
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