linux-kernel - Re: [RFC v3 0/2] CPU-Idle latency selftest framework

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Message-ID: <CAAYoRsXqUpkVxDuRUoapBJ__EUPbMBSWJ7QigVcKbr6ApRxzbg@mail.gmail.com>
Date:   Fri, 9 Apr 2021 07:26:38 -0700
From:   Doug Smythies <dsmythies@...us.net>
To:     Pratik Sampat <psampat@...ux.ibm.com>
Cc:     rjw@...ysocki.net, Daniel Lezcano <daniel.lezcano@...aro.org>,
        shuah@...nel.org, ego@...ux.vnet.ibm.com, svaidy@...ux.ibm.com,
        Linux PM list <linux-pm@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-kselftest@...r.kernel.org, pratik.r.sampat@...il.com,
        dsmythies <dsmythies@...us.net>
Subject: Re: [RFC v3 0/2] CPU-Idle latency selftest framework

On Fri, Apr 9, 2021 at 12:43 AM Pratik Sampat <psampat@...ux.ibm.com> wrote:
> On 09/04/21 10:53 am, Doug Smythies wrote:
> > I tried V3 on a Intel i5-10600K processor with 6 cores and 12 CPUs.
> > The core to cpu mappings are:
> > core 0 has cpus 0 and 6
> > core 1 has cpus 1 and 7
> > core 2 has cpus 2 and 8
> > core 3 has cpus 3 and 9
> > core 4 has cpus 4 and 10
> > core 5 has cpus 5 and 11
> >
> > By default, it will test CPUs 0,2,4,6,10 on cores 0,2,4,0,2,4.
> > wouldn't it make more sense to test each core once?
>
> Ideally it would be better to run on all the CPUs, however on larger systems
> that I'm testing on with hundreds of cores and a high a thread count, the
> execution time increases while not particularly bringing any additional
> information to the table.
>
> That is why it made sense only run on one of the threads of each core to make
> the experiment faster while preserving accuracy.
>
> To handle various thread topologies it maybe worthwhile if we parse
> /sys/devices/system/cpu/cpuX/topology/thread_siblings_list for each core and
> use this information to run only once per physical core, rather than
> assuming the topology.
>
> What are your thoughts on a mechanism like this?

Yes, seems like a good solution.

... Doug