Re: 10/7/2014 Weekly Ceph Performance Meeting: kernel boot params

[Andreas Bluemle <andreas.bluemle@itxperts.de>]

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Hi,


On Wed, 8 Oct 2014 16:55:38 -0700
Paul Von-Stamwitz <PVonStamwitz@us.fujitsu.com> wrote:

>  
> > > Hi,
> > >
> > > as mentioned during today's meeting, here are the kernel boot
> > > parameters
> > which I found to provide the basis for good performance results:
> > >
> > >    processor.max_cstate=0
> > >    intel_idle.max_cstate=0
> > >
> > > I understand these to basically turn off any power saving modes
> > > of the
> > CPU; the CPU's we are using are like
> > >   Intel(R) Xeon(R) CPU E5-2640 v2 @ 2.00GHz
> > >   Intel(R) Xeon(R) CPU E5-2630 0 @ 2.30GHz
> > >
> > > At the BIOS level, we
> > >   - turn off Hyperthraeding
> > >   - turn off Turbo mode (in order ot not leave the specifications)
> > >   - turn on frequency floor override
> > >
> > > We also assert that
> > >   /sys/devices/system/cpu/cpu*/cpufreq/scaling_governor
> > >   is set to "performance"
> > >
> > > Using above we see a constant frequency at the maximum level
> > > allowed by
> > the CPU (except Turbo mode).
> > 
> > How much performance do we gain by this? Till now i thought it's
> > just 1-3% so i'm still running ondemand govenor plus power savings.
> 
> As always, it depends. I saw noticeable increases in some throughput
> tests (though I can't recall the % gain.) More important to me was
> that it made my fio results much more consistent. As we measure
> improvements, these settings remove some of the "system noise".
> 
> Best,
> Paul
> 

There were two different aspects which showed improvemnt:
 - code was executed faster
 - thread switching delays were reduced significantly

See the attached grahics. They show processing of a 4 kB write
request: processing at the Pipe::Reader is roughly 200 us in both
pictures, and sth. like 20 us at the OSD::Dispatcher. So there
is not much of a benefit here.

But the delay between the end of the Pipe::Reader and the start
of the OSD::Dispatcher threads reduced really significantly.


(And sorry for the late response)


> > 
> > Greets,
> > Stefan
> > 
> > > Best Regards
> > >
> > > Andreas Bluemle
> > >
> > >
> > >
> > >
> > >
> > >
> > > On Wed, 8 Oct 2014 02:51:21 +0200
> > > Mark Nelson <mark.nelson@inktank.com> wrote:
> > >
> > >> Hi All,
> > >>
> > >> Just a remind that the weekly performance meeting is on
> > >> Wednesdays at 8AM PST.  Same bat time, same bat channel!
> > >>
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> > >>
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> > >
> > >
> > >
> > > --
> > > Andreas Bluemle
> > > mailto:Andreas.Bluemle@itxperts.de ITXperts
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> 



-- 
Andreas Bluemle                     mailto:Andreas.Bluemle@itxperts.de
ITXperts GmbH                       http://www.itxperts.de
Balanstrasse 73, Geb. 08            Phone: (+49) 89 89044917
D-81541 Muenchen (Germany)          Fax:   (+49) 89 89044910

Company details: http://www.itxperts.de/imprint.htm

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