Messages in this thread | | | Date | Wed, 10 Oct 2018 06:44:49 +0100 | From | Javi Merino <> | Subject | Re: [RFC PATCH 0/7] Introduce thermal pressure |
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On Tue, Oct 09, 2018 at 12:24:55PM -0400, 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.
Interesting, I would have sworn that I tested this years ago by lowering the maximum frequency of a cpufreq domain, and the scheduler reacted accordingly to the new maximum capacities of the cpus.
> 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 ++++++++++++-
thermal? There are other ways in which the maximum frequency of a cpu can be limited, for example from userspace via scaling_max_freq.
When something (anything) changes the maximum frequency of a cpufreq policy, the scheduler should be notified. I think this change should be done in cpufreq instead to make it generic and not particular to a given maximum frequency "capper".
Cheers, Javi
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