linux-kernel - Re: [RFC PATCH v4 0/2] cpuidle: teo: Introduce util-awareness

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Date:   Sun, 27 Nov 2022 14:36:39 +0800
From:   Zhang Rui <rui.zhang@...el.com>
To:     Doug Smythies <dsmythies@...us.net>
Cc:     daniel.lezcano@...aro.org, lukasz.luba@....com,
        Dietmar.Eggemann@....com, yu.chen.surf@...il.com,
        linux-pm@...r.kernel.org, linux-kernel@...r.kernel.org,
        'Kajetan Puchalski' <kajetan.puchalski@....com>,
        rafael@...nel.org
Subject: Re: [RFC PATCH v4 0/2] cpuidle: teo: Introduce util-awareness

On Sat, 2022-11-26 at 13:56 -0800, Doug Smythies wrote:
> 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.
>  
Got it.

> > > 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".

I just checked the code. My understanding is that
"above" means the previous idle state residency is too short, and a
shallower state would have been a better match.
"below" means the previous idle state residency is too long, and a
deeper state would have been a better match.

So probably "above" means "should be shallower" or "was too deep", and
"below" means "should be deeper" or "was to shallow"?

thanks,
rui