* Re: Preemption patch, some more feedback
[not found] <Pine.LNX.4.30.0109101132410.4681-100000@toy.mandrakesoft.com>
@ 2001-09-10 21:26 ` Robert Love
0 siblings, 0 replies; only message in thread
From: Robert Love @ 2001-09-10 21:26 UTC (permalink / raw)
To: linux-kernel
On Mon, 2001-09-10 at 11:41, Francis Galiegue wrote:
> Machine is Athlon 650, AMD Viper chipset, 256 MB RAM. Kernel is
> 2.4.9-ac10 + preempt patch + irc_conntrack patch from iptables.
>
> The preempt patch largely improves multimedia latency (no surprise on
> that), I can watch a DivX smoothly (with mplayer, gfx being Matrox G400)
> and compile various stuff behind.
>
> However, a very simple command destroys this completely:
>
> cat /dev/zero >/dev/null
>
> DivX playback then becomes sluggish, no visible difference in this case
> between stock kernel and "preempt" kernel.
A long-term lock must be held for the duration of `cat /dev/zero >
/dev/null' -- i dont know if it is in the access to /dev/null or
/dev/zero or in the basic file operation itself.
as long as a lock is held, preemption can not occur.
what do we do? for the short term, and the benefit of everyone (UP, SMP,
and preemption users) we need to eliminate long-held locks with a better
solution.
in the long term, we can look at having the preemption patch use various
different types of locks (priority locks, spin then sleep locks, etc.)
--
Robert M. Love
rml at ufl.edu
rml at tech9.net
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