RE: [RFC PATCH v4 0/2] cpuidle: teo: Introduce util-awareness

["Doug Smythies" <dsmythies@telus.net>]

On 2022.11.26 08:26 Rui wrote:
> On Wed, 2022-11-23 at 20:08 -0800, Doug Smythies wrote:
>> On 2022.11.21 04:23 Kajetan Puchalski wrote:
>>> On Wed, Nov 02, 2022 at 03:28:06PM +0000, Kajetan Puchalski wrote:
>>> 
>>> [...]
>>> 
>>>> v3 -> v4:
>>>> - remove the chunk of code skipping metrics updates when the CPU
>>>> was utilized
>>>> - include new test results and more benchmarks in the cover
>>>> letter
>>> 
>>> [...]
>>> 
>>> It's been some time so I just wanted to bump this, what do you
>>> think
>>> about this v4? Doug has already tested it, resuls for his machine
>>> are
>>> attached to the v3 thread.
>> 
>> Hi All,
>> 
>> I continued to test this and included the proposed ladder idle
>> governor in my continued testing.
>> (Which is why I added Rui as an addressee)
>
> Hi, Doug,

Hi Rui,

> Really appreciated your testing data on this.
> I have some dumb questions and I need your help so that I can better
> understand some of the graphs. :)
>
>> However, I ran out of time. Here is what I have:
>> 
>> Kernel: 6.1-rc3 and with patch sets
>> Processor: Intel(R) Core(TM) i5-10600K CPU @ 4.10GHz
>> CPU scaling driver: intel_cpufreq
>> HWP disabled.
>> Unless otherwsie stated, performance CPU scaling govenor.
>> 
>> Legend:
>> teo: the current teo idle governor
>> util-v4: the RFC utilization teo patch set version 4.
>> menu: the menu idle governor
>> ladder-old: the current ladder idle governor
>> ladder: the RFC ladder patchset.
>> 
>> Workflow: shell-intensive serialized workloads.
>> Variable: PIDs per second.
>> Note: Single threaded.
>> Master reference: forced CPU affinity to 1 CPU.

This is the 1cpu on the graph.

>> Performance Results:
>> http://smythies.com/~doug/linux/idle/teo-util/graphs/pids-perf.png
>> Schedutil Results:
>> http://smythies.com/~doug/linux/idle/teo-util/graphs/pids-su.png
>
> what does 1cpu mean?

For shell-intensive serialized workflow or:

Dountil the list of tasks is finished:
    Start the next task in the list of stuff to do (with a new PID).
    Wait for it to finish
Enduntil

We know it represents a challenge for CPU frequency scaling drivers,
schedulers, and therefore idle drivers.

We also know that the best performance is achieved by overriding
the scheduler and forcing CPU affinity. I use this "best" case as the
master reference, using the label 1cpu on the graph.
 
>> Workflow: sleeping ebizzy 128 threads.
>> Variable: interval (uSecs).
>> Performance Results:
>> http://smythies.com/~doug/linux/idle/teo-util/graphs/ebizzy-128-perf.png
>> Performance power and idle data:
>> http://smythies.com/~doug/linux/idle/teo-util/ebizzy/perf/
>
> for the "Idle state 0/1/2/3 was too deep" graphs, may I know how you
> assert that an idle state is too deep/shallow?

I get those stats directly from the kernel driver statistics. For example:

$ grep . /sys/devices/system/cpu/cpu4/cpuidle/state*/above
/sys/devices/system/cpu/cpu4/cpuidle/state0/above:0
/sys/devices/system/cpu/cpu4/cpuidle/state1/above:38085
/sys/devices/system/cpu/cpu4/cpuidle/state2/above:7668
/sys/devices/system/cpu/cpu4/cpuidle/state3/above:6823

$ grep . /sys/devices/system/cpu/cpu4/cpuidle/state*/below
/sys/devices/system/cpu/cpu4/cpuidle/state0/below:72059
/sys/devices/system/cpu/cpu4/cpuidle/state1/below:246573
/sys/devices/system/cpu/cpu4/cpuidle/state2/below:7817
/sys/devices/system/cpu/cpu4/cpuidle/state3/below:0

I keep track of the changes per sample interval and graph
the sum for all CPUs as a percentage of the usage of
that idle state.

Because I can never remember what "above" and "below"
actually mean, I use the terms "was too shallow"
and "was too deep".

... Doug