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Subject: Re: [PATCH v3 0/2] Selftest for cpuidle latency measurement
To:     Pratik Rajesh Sampat <psampat@linux.ibm.com>, rjw@rjwysocki.net,
        mpe@ellerman.id.au, benh@kernel.crashing.org, paulus@samba.org,
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        pratik.r.sampat@gmail.com, linux-pm@vger.kernel.org,
        linuxppc-dev@lists.ozlabs.org, linux-kernel@vger.kernel.org,
        linux-kselftest@vger.kernel.org
References: <20200721124300.65615-1-psampat@linux.ibm.com>
From:   Daniel Lezcano <daniel.lezcano@linaro.org>
Message-ID: <17e884b8-09d8-98a8-3890-bf506d2cdfca@linaro.org>
Date:   Tue, 21 Jul 2020 16:57:56 +0200
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On 21/07/2020 14:42, Pratik Rajesh Sampat wrote:
> v2: https://lkml.org/lkml/2020/7/17/369
> Changelog v2-->v3
> Based on comments from Gautham R. Shenoy adding the following in the
> selftest,
> 1. Grepping modules to determine if already loaded
> 2. Wrapper to enable/disable states
> 3. Preventing any operation/test on offlined CPUs 
> ---
> 
> The patch series introduces a mechanism to measure wakeup latency for
> IPI and timer based interrupts
> The motivation behind this series is to find significant deviations
> behind advertised latency and resisdency values

Why do you want to measure for the timer and the IPI ? Whatever the
source of the wakeup, the exit latency remains the same, no ?

Is all this kernel-ish code really needed ?

What about using a highres periodic timer and make it expires every eg.
50ms x 2400, so it is 120 secondes and measure the deviation. Repeat the
operation for each idle states.

And in order to make it as much accurate as possible, set the program
affinity on a CPU and isolate this one by preventing other processes to
be scheduled on and migrate the interrupts on the other CPUs.

That will be all userspace code, no?


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