linux-kernel - Re: [RFC v3 1/2] powerpc/cpuidle: cpuidle wakeup latency based on IPI and timer events

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Date:   Fri, 22 Sep 2023 09:41:14 +1000
From:   Michael Ellerman <mpe@...erman.id.au>
To:     Aboorva Devarajan <aboorvad@...ux.vnet.ibm.com>
Cc:     sshegde@...ux.vnet.ibm.com, srikar@...ux.vnet.ibm.com,
        npiggin@...il.com, rmclure@...ux.ibm.com, arnd@...db.de,
        joel@....id.au, shuah@...nel.org, linux-kselftest@...r.kernel.org,
        linuxppc-dev@...ts.ozlabs.org, linux-kernel@...r.kernel.org,
        pratik.r.sampat@...il.com
Subject: Re: [RFC v3 1/2] powerpc/cpuidle: cpuidle wakeup latency based on
 IPI and timer events

Aboorva Devarajan <aboorvad@...ux.vnet.ibm.com> writes:
> On Wed, 2023-09-13 at 08:54 +1000, Michael Ellerman wrote:
>> Aboorva Devarajan <aboorvad@...ux.vnet.ibm.com> writes:
>> > From: Pratik R. Sampat <psampat@...ux.ibm.com>
>> > 
>> > Introduce a mechanism to fire directed IPIs from a source CPU to a
>> > specified target CPU and measure the time incurred on waking up the
>> > target CPU in response.
>> > 
>> > Also, introduce a mechanism to queue a hrtimer on a specified CPU
>> > and
>> > subsequently measure the time taken to wakeup the CPU.
>> > 
>> > Define a simple debugfs interface that allows for adjusting the
>> > settings to trigger IPI and timer events on a designated CPU, and
>> > to
>> > observe the resulting cpuidle wakeup latencies.
>> > 
>> > Reviewed-by: Srikar Dronamraju <srikar@...ux.vnet.ibm.com>
>> > Signed-off-by: Pratik R. Sampat <psampat@...ux.ibm.com>
>> > Signed-off-by: Aboorva Devarajan <aboorvad@...ux.vnet.ibm.com>
>> > ---
>> >  arch/powerpc/Kconfig.debug                 |  10 ++
>> >  arch/powerpc/kernel/Makefile               |   1 +
>> >  arch/powerpc/kernel/test_cpuidle_latency.c | 154
>> > +++++++++++++++++++++
>>   
>> I don't see anything here that's powerpc specific?
>> 
>> Which makes me wonder 1) could this be done with some existing
>> generic
>> mechanism?, and 2) if not can this test code be made generic.
>> 
>> At the very least this should be Cc'ed to the cpuidle lists &
>> maintainers given it's a test for cpuidle latency :)
>> 
>> cheers
>
> Hi Michael,
>
> Thanks a lot for taking a look at this.
>
> Yes, this test-case can be used as a generic benchmark for evaluating
> CPU idle latencies across different architectures, as it has thus far
> been exclusively tested and used on PowerPC, so we thought it would be
> more beneficial to incorporate it into a PowerPC specific self-test
> suite. But I will work on making it a generic self-test and send across
> a v4.

I'd suggest just posting v3 again but Cc'ing the cpuidle lists &
maintainers, to see if there is any interest in making it generic.

cheers