[9fans] kernel - kmapinval?

[9fans] kernel - kmapinval?

[Tim Newsham]

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.

Re: [9fans] kernel - kmapinval?

[Russ Cox]

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.
>

Re: [9fans] kernel - kmapinval?

[jmk]

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

Re: [9fans] kernel - kmapinval?

[William Josephson]

On Sun, Nov 28, 2004 at 11:52:27AM -0500, jmk@plan9.bell-labs.com wrote:
> On a related note, has anyone used the cpu performance counters
> on the x86 with Plan 9?

Only in the kernel.

Re: [9fans] kernel - kmapinval?

[Scott Schwartz]

| On a related note, has anyone used the cpu performance counters
| on the x86 with Plan 9?
 
I have.  I posted patches a long time ago (3rd edition) to give them
#c files and to keep per-process statistics.

Re: [9fans] kernel - kmapinval?

[Ronald G. Minnich]

On Sun, 28 Nov 2004, Scott Schwartz wrote:

> I have.  I posted patches a long time ago (3rd edition) to give them
> #c files and to keep per-process statistics.


I'll take them if you have them, ... 

ron