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SubjectRe: Lockups - lost interrupt

On Mon, 13 Sep 1999 yodaiken@chelm.cs.nmt.edu wrote:

> > i'm not sure wether this will ever be accepted into the main kernel -
> > __cli()/__sti()/etc. right now is heavily used and inlined (mostly via
>
> The price is paid only if you select RTL in config.
> my idea is that system.h does

oh, ok. I thought you want to do this 'runtime', by patching a pretty
normal kernel dynamically.

> Lmbench can't detect any performance loss -- remember that cli and sti
> are not cheap instructions anyways.

they are ~7 cycles, but the real cost is the slight kernel bloat (== more
cache footprint) caused by the inlined function call. Anyway, this is of
course not a problem for an optional thing, i thought you are trying to do
this runtime as well.

> > spinlocks) and it's a single instruction. Maybe building a table of 'cli,
> > sti, popfl, pushfl' addresses into a special section can do the trick
> > without interfering with the 'normal' kernel? A single-instruction 'int 3'
> > could be patched into those places, or something like that.
>
> The "int" would cost too much in the rtl case. On

the int is basically a function call if you do it on ring 0, but yes it's
more expensive than a normal function call.

> the other hand, I had thought of
> of a section. Not sure what the advantage would be. With the structure,
> the compiler generates
>
> movel N+irq_desc,%eax
> call *%eax

if the int3 solution is implementable (it's a tough problem i think), the
advantage would be a completely unaffected 'main kernel'. RTL could be
switched on/off runtime. OTOH, people recompile kernels routinely anyway.

-- mingo


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