Re: [RFC PATCH 0/7] Introduce thermal pressure

[Thara Gopinath <thara.gopinath@linaro.org>]

Hello Lukasz,

On 10/10/2018 11:35 AM, Lukasz Luba wrote:
> Hi Thara,
> 
> I have run it on Exynos5433 mainline.
> When it is enabled with step_wise thermal governor,
> some of my tests are showing ~30-50% regression (i.e. hackbench),
> dhrystone ~10%.

That is interesting. If I understand correctly, dhrystone spawns 16
threads or so and floods the system. In "theory", such a test should not
see any performance improvement and degradation. What is the thermal
activity like in your system? I will try running one of these tests on
hikey960.
> 
> Could you tell me which thermal governor was used in your case?
> Please also share the name of that benchmark, i will give it a try.
> Is it single threaded compute-intensive?

Step-wise governor.
I use aobench which is part of phoronix-test-suite.

Regards
Thara

> 
> Regards,
> Lukasz
> 
> On 10/09/2018 06:24 PM, Thara Gopinath wrote:
>> Thermal governors can respond to an overheat event for a cpu by
>> capping the cpu's maximum possible frequency. This in turn
>> means that the maximum available compute capacity of the
>> cpu is restricted. But today in linux kernel, in event of maximum
>> frequency capping of a cpu, the maximum available compute
>> capacity of the cpu is not adjusted at all. In other words, scheduler
>> is unware maximum cpu capacity restrictions placed due to thermal
>> activity. This patch series attempts to address this issue.
>> The benefits identified are better task placement among available
>> cpus in event of overheating which in turn leads to better
>> performance numbers.
>>
>> The delta between the maximum possible capacity of a cpu and
>> maximum available capacity of a cpu due to thermal event can
>> be considered as thermal pressure. Instantaneous thermal pressure
>> is hard to record and can sometime be erroneous as there can be mismatch
>> between the actual capping of capacity and scheduler recording it.
>> Thus solution is to have a weighted average per cpu value for thermal
>> pressure over time. The weight reflects the amount of time the cpu has
>> spent at a capped maximum frequency. To accumulate, average and
>> appropriately decay thermal pressure, this patch series uses pelt
>> signals and reuses the available framework that does a similar
>> bookkeeping of rt/dl task utilization.
>>
>> Regarding testing, basic build, boot and sanity testing have been
>> performed on hikey960 mainline kernel with debian file system.
>> Further aobench (An occlusion renderer for benchmarking realworld
>> floating point performance) showed the following results on hikey960
>> with debain.
>>
>>                                          Result          Standard        Standard
>>                                          (Time secs)     Error           Deviation
>> Hikey 960 - no thermal pressure applied 138.67          6.52            11.52%
>> Hikey 960 -  thermal pressure applied   122.37          5.78            11.57%
>>
>> Thara Gopinath (7):
>>    sched/pelt: Add option to make load and util calculations frequency
>>      invariant
>>    sched/pelt.c: Add support to track thermal pressure
>>    sched: Add infrastructure to store and update instantaneous thermal
>>      pressure
>>    sched: Initialize per cpu thermal pressure structure
>>    sched/fair: Enable CFS periodic tick to update thermal pressure
>>    sched/fair: update cpu_capcity to reflect thermal pressure
>>    thermal/cpu-cooling: Update thermal pressure in case of a maximum
>>      frequency capping
>>
>>   drivers/base/arch_topology.c  |  1 +
>>   drivers/thermal/cpu_cooling.c | 20 ++++++++++++-
>>   include/linux/sched.h         | 14 +++++++++
>>   kernel/sched/Makefile         |  2 +-
>>   kernel/sched/core.c           |  2 ++
>>   kernel/sched/fair.c           |  4 +++
>>   kernel/sched/pelt.c           | 40 ++++++++++++++++++--------
>>   kernel/sched/pelt.h           |  7 +++++
>>   kernel/sched/sched.h          |  1 +
>>   kernel/sched/thermal.c        | 66 +++++++++++++++++++++++++++++++++++++++++++
>>   kernel/sched/thermal.h        | 13 +++++++++
>>   11 files changed, 157 insertions(+), 13 deletions(-)
>>   create mode 100644 kernel/sched/thermal.c
>>   create mode 100644 kernel/sched/thermal.h
>>


-- 
Regards
Thara