Messages in this thread |  | | Subject | Re: Preemption patch, some more feedback | From | Robert Love <> | Date | 10 Sep 2001 17:26:08 -0400 |
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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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