Re: What is the truth about Linux 2.4's RAM limitations?

Jonathan Lundell
2001-07-10T22:07:46Z

At 4:49 PM -0500 2001-07-10, Jesse Pollard wrote:
> > A full cache flush would be needed at every entry into the kernel,
>> including hardware interrupts. Very poor for performance.
>>
>> Why would a cache flush be necessary at all? I assume ia32 caches
>> where physically not virtually mapped?
>
>Because the entire virtual mapping is replaced by that of the kernel.
>This would invalidate the entire cache table. It was also pointed out
>that this would have to be done for every interrupt too.

If the cache were physically indexed and tagged, this would not be
the case; changes in mapping would be irrelevant. If someone has a
reference that describes IA-32 cache tags in detail, I'd like to know
about it.

TLBs are another story, though on some other architectures they're
not a problem either. UltraSPARC, for example, maps the entire kernel
with a couple or three reserved TLB entries (at least Solaris does).
Of course, SPARC has hardware contexts, which are helpful in this
regard.
--
/Jonathan Lundell.