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Date:   Thu, 29 Apr 2021 18:32:06 -0300
From:   Arnaldo Carvalho de Melo <acme@kernel.org>
To:     Muni Sekhar <munisekharrms@gmail.com>
Cc:     peter enderborg <peter.enderborg@sony.com>,
        Greg KH <greg@kroah.com>,
        kernelnewbies <kernelnewbies@kernelnewbies.org>,
        linux-kernel@vger.kernel.org, linux-perf-users@vger.kernel.org
Subject: Re: Scheduler benchmarks
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Em Wed, Aug 19, 2020 at 03:46:06PM +0530, Muni Sekhar escreveu:
> On Tue, Aug 18, 2020 at 11:45 PM peter enderborg <peter.enderborg@sony.com> wrote:
> > On 8/18/20 7:53 PM, Muni Sekhar wrote:
> > > On Tue, Aug 18, 2020 at 11:06 PM Greg KH <greg@kroah.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@kroah.com> wrote:
> > >> 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.

This made me remember Lisbon:

http://vger.kernel.org/~acme/perf/bpf-is-eating-the-world-dont-you-see-lpc-lisbon-2019/#/8/2

Greg was there when this slide was first shown... ;-)

Look at the icache misses when the kernel is entered (syscall entry).

Then add this to the kernel command line: "nospectre_v1 nospectre_v2"

And see what happens:

http://vger.kernel.org/~acme/perf/bpf-is-eating-the-world-dont-you-see-lpc-lisbon-2019/#/8/3

So using these (and any new ones related to disabling hardware flaw
mitigation) maybe a way to analyse this, if you haven't figured this out
yet, sorry for the huge delay in replying 8-)

- Arnaldo
 
> >
> > 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

-- 

- Arnaldo