[RFC,6/7] sched/fair: update cpu_capcity to reflect thermal pressure
diff mbox series

Message ID 1539102302-9057-7-git-send-email-thara.gopinath@linaro.org
State RFC, archived
Headers show
Series
  • Introduce thermal pressure
Related show

Commit Message

Thara Gopinath Oct. 9, 2018, 4:25 p.m. UTC
cpu_capacity relflects the maximum available capacity of a cpu. Thermal
pressure on a cpu means this maximum available capacity is reduced. This
patch reduces the average thermal pressure for a cpu from its maximum
available capacity so that cpu_capacity reflects the actual
available capacity.

Signed-off-by: Thara Gopinath <thara.gopinath@linaro.org>
---
 kernel/sched/fair.c | 1 +
 1 file changed, 1 insertion(+)

Comments

Javi Merino Oct. 10, 2018, 5:57 a.m. UTC | #1
On Tue, Oct 09, 2018 at 12:25:01PM -0400, Thara Gopinath wrote:
> cpu_capacity relflects the maximum available capacity of a cpu. Thermal
> pressure on a cpu means this maximum available capacity is reduced. This
> patch reduces the average thermal pressure for a cpu from its maximum
> available capacity so that cpu_capacity reflects the actual
> available capacity.
> 
> Signed-off-by: Thara Gopinath <thara.gopinath@linaro.org>
> ---
>  kernel/sched/fair.c | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> index 7deb1d0..8651e55 100644
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -7497,6 +7497,7 @@ static unsigned long scale_rt_capacity(int cpu)
>  
>  	used = READ_ONCE(rq->avg_rt.util_avg);
>  	used += READ_ONCE(rq->avg_dl.util_avg);
> +	used += READ_ONCE(rq->avg_thermal.load_avg);

IIUIC, you are treating thermal pressure as an artificial load on the
cpu.  If so, this sounds like a hard to maintain hack.  Thermal
pressure have different characteristics to utilization.  What happens
if thermal sets the cpu cooling state back to 0 because there is
thermal headroom again?  Do we keep adding this artificial load to the
cpu just because there was thermal pressure in the past and let it
decay as if it was cpu load?

Cheers,
Javi
Thara Gopinath Oct. 10, 2018, 2:22 p.m. UTC | #2
On 10/10/2018 01:57 AM, Javi Merino wrote:
> On Tue, Oct 09, 2018 at 12:25:01PM -0400, Thara Gopinath wrote:
>> cpu_capacity relflects the maximum available capacity of a cpu. Thermal
>> pressure on a cpu means this maximum available capacity is reduced. This
>> patch reduces the average thermal pressure for a cpu from its maximum
>> available capacity so that cpu_capacity reflects the actual
>> available capacity.
>>
>> Signed-off-by: Thara Gopinath <thara.gopinath@linaro.org>
>> ---
>>  kernel/sched/fair.c | 1 +
>>  1 file changed, 1 insertion(+)
>>
>> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
>> index 7deb1d0..8651e55 100644
>> --- a/kernel/sched/fair.c
>> +++ b/kernel/sched/fair.c
>> @@ -7497,6 +7497,7 @@ static unsigned long scale_rt_capacity(int cpu)
>>  
>>  	used = READ_ONCE(rq->avg_rt.util_avg);
>>  	used += READ_ONCE(rq->avg_dl.util_avg);
>> +	used += READ_ONCE(rq->avg_thermal.load_avg);
> 
> IIUIC, you are treating thermal pressure as an artificial load on the
> cpu.  If so, this sounds like a hard to maintain hack.  Thermal
> pressure have different characteristics to utilization.  What happens
> if thermal sets the cpu cooling state back to 0 because there is
> thermal headroom again?  Do we keep adding this artificial load to the
> cpu just because there was thermal pressure in the past and let it
> decay as if it was cpu load?

Setting cpu cooling state back to 0 will decay the thermal pressure back
to 0 ? Yes, cpu will not register an instantaneous drop in the cap, it
will be decayed down following the PELT signals.

> 
> Cheers,
> Javi
>

Patch
diff mbox series

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 7deb1d0..8651e55 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -7497,6 +7497,7 @@  static unsigned long scale_rt_capacity(int cpu)
 
 	used = READ_ONCE(rq->avg_rt.util_avg);
 	used += READ_ONCE(rq->avg_dl.util_avg);
+	used += READ_ONCE(rq->avg_thermal.load_avg);
 
 	if (unlikely(used >= max))
 		return 1;