On 09/01/2024 14:29, Vincent Guittot wrote:
> On Tue, 9 Jan 2024 at 12:34, Dietmar Eggemann <dietmar.eggemann@xxxxxxx> wrote:
>>
>> On 08/01/2024 14:48, Vincent Guittot wrote:
>>> Following the consolidation and cleanup of CPU capacity in [1], this serie
>>> reworks how the scheduler gets the pressures on CPUs. We need to take into
>>> account all pressures applied by cpufreq on the compute capacity of a CPU
>>> for dozens of ms or more and not only cpufreq cooling device or HW
>>> mitigiations. we split the pressure applied on CPU's capacity in 2 parts:
>>> - one from cpufreq and freq_qos
>>> - one from HW high freq mitigiation.
>>>
>>> The next step will be to add a dedicated interface for long standing
>>> capping of the CPU capacity (i.e. for seconds or more) like the
>>> scaling_max_freq of cpufreq sysfs. The latter is already taken into
>>> account by this serie but as a temporary pressure which is not always the
>>> best choice when we know that it will happen for seconds or more.
>>
>> I guess this is related to the 'user space system pressure' (*) slide of
>> your OSPM '23 talk.
>
> yes
>
>>
>> Where do you draw the line when it comes to time between (*) and the
>> 'medium pace system pressure' (e.g. thermal and FREQ_QOS).
>
> My goal is to consider the /sys/../scaling_max_freq as the 'user space
> system pressure'
>
>>
>> IIRC, with (*) you want to rebuild the sched domains etc.
>
> The easiest way would be to rebuild the sched_domain but the cost is
> not small so I would prefer to skip the rebuild and add a new signal
> that keep track on this capped capacity
Are you saying that you don't need to rebuild sched domains since
cpu_capacity information of the sched domain hierarchy is
independently updated via:
update_sd_lb_stats() {
update_group_capacity() {
if (!child)
update_cpu_capacity(sd, cpu) {
capacity = scale_rt_capacity(cpu) {
max = get_actual_cpu_capacity(cpu) <- (*)
}
sdg->sgc->capacity = capacity;
sdg->sgc->min_capacity = capacity;
sdg->sgc->max_capacity = capacity;
}
}
}
(*) influence of temporary and permanent (to be added) frequency
pressure on cpu_capacity (per-cpu and in sd data)
example: hackbench on h960 with IPA:
cap min max
...
hackbench-2284 [007] .Ns.. 2170.796726: update_group_capacity: sdg !child cpu=7 1017 1017 1017
hackbench-2456 [007] ..s.. 2170.920729: update_group_capacity: sdg !child cpu=7 1018 1018 1018
<...>-2314 [007] ..s1. 2171.044724: update_group_capacity: sdg !child cpu=7 1011 1011 1011
hackbench-2541 [007] ..s.. 2171.168734: update_group_capacity: sdg !child cpu=7 918 918 918
hackbench-2558 [007] .Ns.. 2171.228716: update_group_capacity: sdg !child cpu=7 912 912 912
<...>-2321 [007] ..s.. 2171.352718: update_group_capacity: sdg !child cpu=7 812 812 812
hackbench-2553 [007] ..s.. 2171.476721: update_group_capacity: sdg !child cpu=7 640 640 640
<...>-2446 [007] ..s2. 2171.600743: update_group_capacity: sdg !child cpu=7 610 610 610
hackbench-2347 [007] ..s.. 2171.724738: update_group_capacity: sdg !child cpu=7 406 406 406
hackbench-2331 [007] .Ns1. 2171.848768: update_group_capacity: sdg !child cpu=7 390 390 390
hackbench-2421 [007] ..s.. 2171.972733: update_group_capacity: sdg !child cpu=7 388 388 388
...
