Subject: Re: [linux-audio-dev] interesting 2.3.4* kernel statistic
From: Roger Larsson (roger.larsson_AT_norran.net)
Date: ti helmi 22 2000 - 13:45:21 EST
Benno Senoner wrote:
>
> On Tue, 22 Feb 2000, David Olofson wrote:
> > On Sun, 20 Feb 2000, Paul Barton-Davis wrote:
> > > Someone on linux-kernel ran SGI's lockmeter, and notes:
> > >
> > > P.S.: some good news: except do_close
> > ^^^^^^^^
> > When does this happen?
> >
> > > [up to 34 milliseconds], noone
> > ^^^^
> > *aaaargh!* Can'n happen that often, right?
> > (OTOH, this might be good news for *us*...! >:-D )
> >
> > > else owns a spinlock for more than 3 milliseconds.
> > ^^^
> > Seems like a very long time
> > for a lock in a kernel that's supposed to do real time...
> >
> > > I don't know if this is "good" news, but there we have it.
> >
> > Well, to me it seem like another "Oh, I thought we had some
> > competition *there*, at least..." Perhaps we do, but these figures
> > aren't as impressive as one would expect from a *preemptive* kernel.
> > After all, making a kernel preemptive (viewed per CPU, that is), is
> > to great extent a performance hack for this kind of things... As we
> > can see on Linux + the lowlatency patches, it's not really needed! :-)
> >
> >
> > //David
>
> I am a little confused by the numbers:
> With the lowlatency patches we achieve <2-3ms latencies ALWAYS,
> even when closing files etc.
> Latencytest ran on my P133 while accessing the disk heavily , stress proc ,
> and copying the entrire content of two CDs from TWO CDROM drives
> simultaneously, and a close() call is issued zillions of time during my tests.
>
> Therefore I don't understand how/if the lockmetering can be applied to do any
> inferency on how small latencies we can get out of our realtime apps.
>
a) Tested on an unpatched 2.2.x
b) Tested on current 2.3.x. Basically unpatched too since I have not
seen
Ingo M. announce his 2.3 patch yet. Some things are fixed during
development.
I.e with the version tested your worst case will be at least 34 ms.
Since several locks might be taken during one kernel operation.
/RogerL
> Benno.
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