Re: [RFC PATCH 0/7] Introduce thermal pressure
From: Thara Gopinath
Date: Wed Oct 10 2018 - 13:31:03 EST
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
> 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?
I use aobench which is part of phoronix-test-suite.
> 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
>> sched/pelt.c: Add support to track thermal pressure
>> sched: Add infrastructure to store and update instantaneous thermal
>> 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