linux-kernel - Re: Scheduler benchmarks

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Message-ID: <CAHhAz+iC_F5w5EoZP8-dBNm+DV0uNMva6Mr2uBdmZtejL1OH-w@mail.gmail.com>
Date:   Wed, 19 Aug 2020 15:46:06 +0530
From:   Muni Sekhar <munisekharrms@...il.com>
To:     peter enderborg <peter.enderborg@...y.com>
Cc:     Greg KH <greg@...ah.com>,
        kernelnewbies <kernelnewbies@...nelnewbies.org>,
        linux-kernel@...r.kernel.org, linux-perf-users@...r.kernel.org
Subject: Re: Scheduler benchmarks

On Tue, Aug 18, 2020 at 11:45 PM peter enderborg
<peter.enderborg@...y.com> wrote:
>
> On 8/18/20 7:53 PM, Muni Sekhar wrote:
> > On Tue, Aug 18, 2020 at 11:06 PM Greg KH <greg@...ah.com> wrote:
> >> On Tue, Aug 18, 2020 at 11:01:35PM +0530, Muni Sekhar wrote:
> >>> On Tue, Aug 18, 2020 at 10:44 PM Greg KH <greg@...ah.com> wrote:
> >>>> On Tue, Aug 18, 2020 at 10:24:13PM +0530, Muni Sekhar wrote:
> >>>>> On Tue, Aug 18, 2020 at 8:06 PM Greg KH <greg@...ah.com> wrote:
> >>>>>> On Tue, Aug 18, 2020 at 08:00:11PM +0530, Muni Sekhar wrote:
> >>>>>>> Hi all,
> >>>>>>>
> >>>>>>> I’ve two identical Linux systems with only kernel differences.
> >>>>>> What are the differences in the kernels?
> >>>> You didn't answer this question, is this the same kernel source being
> >>>> compared here?  Same version?  Same compiler?  Everything identical?
> >>> Both systems are having exactly the same hardware configuration.
> >>> Compiler and kernel versions are different. One system has Ubuntu
> >>> 16.04.4 LTS(4.4.0-66-generic kernel with gcc version 5.4.0) kernel and
> >>> the other one has Ubuntu 18.04.4 LTS(4.15.0-91-generic kernel with gcc
> >>> version 7.5.0).
> >> Those are _very_ different kernel versions, with many years and tens of
> >> thousands of different changes between them.
> >>
> >> Hopefully the newer kernel is faster, so just stick with that :)
> > But unfortunately the newer kernel is very slow, that is the reason
> > for starting this investigation :)
> > Any type of help,  and guidelines to dive deeper will be highly appreciated.
>
> On the 4.4 kernel you dont have
>
> +CONFIG_RETPOLINE=y
> +CONFIG_INTEL_RDT=y
Thanks! That is helpful. Yes, I see 4.4 kernel don't have the above
two config options.
What analysis can be done to narrow down the root cause?
Any example of reference could be helpful to understand.

>
> And your base is very different two.
>
> Try to use mainline on both system and see.
>
> You can also use the same base kernel version from ubuntu and
>
> run your test.
>
>
> >> greg k-h
> >
> >
>


-- 
Thanks,
Sekhar