linux-kernel - Re: [PATCH v3 0/2] Selftest for cpuidle latency measurement

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <17e884b8-09d8-98a8-3890-bf506d2cdfca@linaro.org>
Date:   Tue, 21 Jul 2020 16:57:56 +0200
From:   Daniel Lezcano <daniel.lezcano@...aro.org>
To:     Pratik Rajesh Sampat <psampat@...ux.ibm.com>, rjw@...ysocki.net,
        mpe@...erman.id.au, benh@...nel.crashing.org, paulus@...ba.org,
        srivatsa@...il.mit.edu, shuah@...nel.org, npiggin@...il.com,
        ego@...ux.vnet.ibm.com, svaidy@...ux.ibm.com,
        pratik.r.sampat@...il.com, linux-pm@...r.kernel.org,
        linuxppc-dev@...ts.ozlabs.org, linux-kernel@...r.kernel.org,
        linux-kselftest@...r.kernel.org
Subject: Re: [PATCH v3 0/2] Selftest for cpuidle latency measurement

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?





-- 
<http://www.linaro.org/> Linaro.org │ Open source software for ARM SoCs

Follow Linaro:  <http://www.facebook.com/pages/Linaro> Facebook |
<http://twitter.com/#!/linaroorg> Twitter |
<http://www.linaro.org/linaro-blog/> Blog