Re: [PATCH] 2.4.0-prerelease: preemptive kernel.

Daniel Phillips
2001-01-04T07:38:06Z

ludovic fernandez wrote:
> The following patch makes the kernel preemptable.
> It is against 2.4.0-prerelease on for i386 only.
> It should work for UP and SMP even though I
> didn't validate it on SMP.
> Comments are welcome.

I was expecting to see this sometime in 2.5, not quite so soon...

The key idea here is to disable preemption on spin lock and reenable on
spin unlock. That's a practical idea, highly compatible with the
current way of doing things. Its a fairly heavy hit on spinlock
performance, but maybe the overall performance hit is small. Benchmarks
are needed.

A more ambitious way to proceed is to change spinlocks so they can sleep
(not in interrupts of course). There would not be any extra overhead
for this on spin_lock (because the sleep test is handled off the fast
path) but spin_unlock gets a little slower - it has to test and jump on
a flag if there are sleepers.

--
Daniel