* [9fans] kernel - kmapinval?
@ 2004-11-27 20:23 Tim Newsham
2004-11-28 1:10 ` Russ Cox
0 siblings, 1 reply; 6+ messages in thread
From: Tim Newsham @ 2004-11-27 20:23 UTC (permalink / raw)
To: 9fans
Hi,
What is kmapinval() used for in the kernel? It appears to be
called only in hzclock() and defined as a no-op in all architectures,
giving little clue as to what its function should be.
Tim N.
^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: [9fans] kernel - kmapinval?
2004-11-27 20:23 [9fans] kernel - kmapinval? Tim Newsham
@ 2004-11-28 1:10 ` Russ Cox
2004-11-28 16:52 ` jmk
0 siblings, 1 reply; 6+ messages in thread
From: Russ Cox @ 2004-11-28 1:10 UTC (permalink / raw)
To: Fans of the OS Plan 9 from Bell Labs
Kmapinval is used on non-x86 multiprocessor architectures,
like the unreleasable port to the SGI machines. The big picture
is that kmap() maps some physical memory so that the kernel
can fiddle with it, kunmap() marks it as unmapped in the
kernel's own data structures, and kmapinval() actually flushes
the entries from the processor or from the software TLB so
that those virtual addresses can be reused for other mappings.
Running kmapinval() lazily at the clock interrupt instead of
on demand avoids the complexities of interprocessor interrupts
and TLB shootdowns.
It is unfortunate that no released architecture source
demonstrates this technique. Should the PC kernels ever get
rewritten to handle larger memories, they'd be a good example.
The carrera sources in 3e have an mmu.c that is about the
same as what was used on the challenge and demonstrates
the technique, even though the carrera was only ever a
uniprocessor.
Russ
On Sat, 27 Nov 2004 10:23:09 -1000 (HST), Tim Newsham <newsham@lava.net> wrote:
> Hi,
>
> What is kmapinval() used for in the kernel? It appears to be
> called only in hzclock() and defined as a no-op in all architectures,
> giving little clue as to what its function should be.
>
> Tim N.
>
^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: [9fans] kernel - kmapinval?
2004-11-28 1:10 ` Russ Cox
@ 2004-11-28 16:52 ` jmk
2004-11-28 17:30 ` William Josephson
2004-11-29 4:58 ` Scott Schwartz
0 siblings, 2 replies; 6+ messages in thread
From: jmk @ 2004-11-28 16:52 UTC (permalink / raw)
To: russcox, 9fans
On Sat Nov 27 20:10:27 EST 2004, russcox@gmail.com wrote:
> ...
> It is unfortunate that no released architecture source
> demonstrates this technique. Should the PC kernels ever get
> rewritten to handle larger memories, they'd be a good example.
> ...
It's likely this will be done in the not too distant future.
On a related note, has anyone used the cpu performance counters
on the x86 with Plan 9?
--jim
^ permalink raw reply [flat|nested] 6+ messages in thread
end of thread, other threads:[~2004-11-29 15:04 UTC | newest]
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2004-11-27 20:23 [9fans] kernel - kmapinval? Tim Newsham
2004-11-28 1:10 ` Russ Cox
2004-11-28 16:52 ` jmk
2004-11-28 17:30 ` William Josephson
2004-11-29 4:58 ` Scott Schwartz
2004-11-29 15:04 ` Ronald G. Minnich
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