linux-kernel - Re: Understanding I/O behaviour

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Date:	Mon, 9 Jul 2007 01:47:48 -0700 (PDT)
From:	Martin Knoblauch <spamtrap@...bisoft.de>
To:	Jesper Juhl <jesper.juhl@...il.com>
Cc:	linux-kernel@...r.kernel.org
Subject: Re: Understanding I/O behaviour


--- Jesper Juhl <jesper.juhl@...il.com> wrote:

> On 05/07/07, Jesper Juhl <jesper.juhl@...il.com> wrote:
> > On 05/07/07, Martin Knoblauch <spamtrap@...bisoft.de> wrote:
> > > Hi,
> > >
> >
> > I'd suspect you can't get both at 100%.
> >
> > I'd guess you are probably using a 100Hz no-preempt kernel.  Have
> you
> > tried a 1000Hz + preempt kernel?   Sure, you'll get a bit lower
> > overall throughput, but interactive responsiveness should be better
> -
> > if it is, then you could experiment with various combinations of
> > CONFIG_PREEMPT, CONFIG_PREEMPT_VOLUNTARY, CONFIG_PREEMPT_NONE and
> > CONFIG_HZ_1000, CONFIG_HZ_300, CONFIG_HZ_250, CONFIG_HZ_100 to see
> > what gives you the best balance between throughput and interactive
> > responsiveness (you could also throw CONFIG_PREEMPT_BKL and/or
> > CONFIG_NO_HZ, but I don't think the impact will be as significant
> as
> > with the other options, so to keep things simple I'd leave those
> out
> > at first) .
> >
> > I'd guess that something like CONFIG_PREEMPT_VOLUNTARY +
> CONFIG_HZ_300
> > would probably be a good compromise for you, but just to see if
> > there's any effect at all, start out with CONFIG_PREEMPT +
> > CONFIG_HZ_1000.
> >
> 
> I'm currious, did you ever try playing around with CONFIG_PREEMPT*
> and
> CONFIG_HZ* to see if that had any noticable impact on interactive
> performance and stuff like logging into the box via ssh etc...?
> 
> -- 
> Jesper Juhl <jesper.juhl@...il.com>
> Don't top-post  http://www.catb.org/~esr/jargon/html/T/top-post.html
> Plain text mails only, please      http://www.expita.com/nomime.html
> 
> 
Hi Jesper,

 my initial kernel was voluntary@...HZ. I have switched to 300HZ, but
have not observed much difference. The config is now:

config-2.6.22-rc7:# CONFIG_PREEMPT_NONE is not set
config-2.6.22-rc7:CONFIG_PREEMPT_VOLUNTARY=y
config-2.6.22-rc7:# CONFIG_PREEMPT is not set
config-2.6.22-rc7:CONFIG_PREEMPT_BKL=y

Cheers


------------------------------------------------------
Martin Knoblauch
email: k n o b i AT knobisoft DOT de
www:   http://www.knobisoft.de
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