Subject: 2.6 preemptive kernel on mips

From: Song Wang <[email-masked]>
Date: Tue, 3 Aug 2004 12:22:44 -0700 (PDT)

Hi,

Has anyone tried to enable kernel preemption on
Linux mips 2.6 kernel (mips32) and test it? If
so, which version does it work?

I tried on 2.6.3 and it didn't work.

Thanks.

-Song

		
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From: Jun Sun <[email-masked]>
Date: Tue, 3 Aug 2004 12:40:48 -0700

> I tried on 2.6.3 and it didn't work.

Try the latest kernel.  I checked preemption around 2.6.5 time
and I believe all the obvious problems are fixed then.

There are still some issues with both SMP and PREEMPT, but most
people won't see them in normal cases.

Jun

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From: Tom Rini <[email-masked]>
Date: Wed, 4 Aug 2004 14:51:40 -0700

> people won't see them in normal cases.

MIPS or generic?  It's claimed, at least, that SMP&&PREEMPT have no
fatal, generic, issues now (I forget if that was the case around 2.6.5).

-- 
Tom Rini
http://gate.crashing.org/~trini/

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From: Jun Sun <[email-masked]>
Date: Wed, 4 Aug 2004 15:25:06 -0700

> fatal, generic, issues now (I forget if that was the case around 2.6.5).

It is MIPS specific problems I was referring to (such as unsafe 
smp_processor_id() reference etc).

If you think about it the real problem is that kernel has non-migratable
regions, a section where process should not migrate from one CPU to
another.  Before preemtible kernel is introduced such non-migratable
regions are not a problem because they can't migrate during those
regions.

So a potentially better solution is to introduce non-migratable
regions during which scheduler promises not to migrate the processes.
Under such promises a process can actually be preempted while
it is in such a region.

Jun