[NTLUG:Discuss] Disk I/O timings.

[Dan Carlson]

Are you using static realtime priorities for your high priority
processes?  If not, this might help make the behavior of the standard
kernel be more predictable for your application.  I wasn't aware until
recently that standard linux supports two types of process priorities,
dynamic and static.  The dynamic priority is the one everyone is
familiar with, viewing with ps or top, controlling with nice, etc.
The static realtime priority is used for processes that must take
precedence over all dynamic priority processes.  On SuSE 7.2 there are
getpriority and setpriority commands that let you view and modify the
static realtime priority of a process.  You can also specify the
realtime scheduling policy you want the process to use, round-robin or
fifo.

I found this to be a good reference on kernel scheduling:

http://www.oreilly.com/catalog/linuxkernel/chapter/ch10.html

Dan Carlson

----- Original Message -----
From: "Steve Baker" <sjbaker1 at airmail.net>
To: <discuss at ntlug.org>
Sent: Friday, December 07, 2001 12:39 AM
Subject: Re: [NTLUG:Discuss] Disk I/O timings.


> Dan Carlson wrote:
> >
> > Are you using one of the realtime or near-realtime linux variants?
> > Presumably they will have much more predictable behavior than a
standard
> > linux kernel.
>
> I'm hoping to be able to manage with an off-the-shelf SuSE.  So far,
that
> seems to be working out quite well.  We had to disable a couple of
daemons
> (things like the cron daemon) - and with those out of the way, I get
hardly
> any disruption to my realtime performance.  Using the 'preemptable
kernel'
> helps too - but even without it, we are doing quite well.
>
> However, I'm aware of the realtime varients and if I have to, I'll
use them.
>
> One of the BIG advantages of using standard Linux is that there is a
massive
> user community where I can ask questions (like this one) and get
intelligent
> answers.  The more off-the-beaten-track you go, the fewer people are
able
> to help in times of trouble.
>
> So, as long as regular Linux can do the job, I'll stick with it.
>
> ----------------------------- Steve
Baker -------------------------------
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