Hi Sasha,
+CC Greg
On 7/5/21 12:05 AM, Sasha Levin wrote:
From: Lukasz Luba lukasz.luba@arm.com
[ Upstream commit 489f16459e0008c7a5c4c5af34bd80898aa82c2d ]
Energy Aware Scheduling (EAS) needs to be able to predict the frequency requests made by the SchedUtil governor to properly estimate energy used in the future. It has to take into account CPUs utilization and forecast Performance Domain (PD) frequency. There is a corner case when the max allowed frequency might be reduced due to thermal. SchedUtil is aware of that reduced frequency, so it should be taken into account also in EAS estimations.
SchedUtil, as a CPUFreq governor, knows the maximum allowed frequency of a CPU, thanks to cpufreq_driver_resolve_freq() and internal clamping to 'policy::max'. SchedUtil is responsible to respect that upper limit while setting the frequency through CPUFreq drivers. This effective frequency is stored internally in 'sugov_policy::next_freq' and EAS has to predict that value.
In the existing code the raw value of arch_scale_cpu_capacity() is used for clamping the returned CPU utilization from effective_cpu_util(). This patch fixes issue with too big single CPU utilization, by introducing clamping to the allowed CPU capacity. The allowed CPU capacity is a CPU capacity reduced by thermal pressure raw value.
Thanks to knowledge about allowed CPU capacity, we don't get too big value for a single CPU utilization, which is then added to the util sum. The util sum is used as a source of information for estimating whole PD energy. To avoid wrong energy estimation in EAS (due to capped frequency), make sure that the calculation of util sum is aware of allowed CPU capacity.
This thermal pressure might be visible in scenarios where the CPUs are not heavily loaded, but some other component (like GPU) drastically reduced available power budget and increased the SoC temperature. Thus, we still use EAS for task placement and CPUs are not over-utilized.
Signed-off-by: Lukasz Luba lukasz.luba@arm.com Signed-off-by: Peter Zijlstra (Intel) peterz@infradead.org Reviewed-by: Vincent Guittot vincent.guittot@linaro.org Reviewed-by: Dietmar Eggemann dietmar.eggemann@arm.com Link: https://lore.kernel.org/r/20210614191128.22735-1-lukasz.luba@arm.com Signed-off-by: Sasha Levin sashal@kernel.org
kernel/sched/fair.c | 11 ++++++++--- 1 file changed, 8 insertions(+), 3 deletions(-)
It has been picked up automatically right? To make it fully working you need also this patch: https://lore.kernel.org/linux-pm/20210614191030.22241-1-lukasz.luba@arm.com/
It makes sure that the thermal pressure signal gets proper information also for CPUs which were offline and then wake-up. It has a proper fix tagging with commit hash id. That patch can be ported to stable: v5.6+ I can send it to stable list. Please let me know if you need any help.
The same applies to patch which I found for v5.13-stable: [PATCH AUTOSEL 5.13 65/85] sched/fair: Take thermal pressure into account while estimating energy https://lore.kernel.org/stable/20210704230420.1488358-65-sashal@kernel.org/T...
Regards, Lukasz