On Wed, 2005-06-01 at 17:22 +1000, [email protected] wrote:
> Andi Kleen <[email protected]> writes:
>
> > fork is only a corner case. The main case is a process allocating
> > memory using brk/mmap and then using it.
>
> Key point: "using it". This normally involves writes to memory. Most
> applications don't commonly read memory that they haven't previously
> written to. (valgrind et al call that behaviour a "bug" :).
Then in that case you have doubled your memory bandwidth
requirement for those cachelines.
>
> Given that, I'd say you really don't want the page zero routines
> touching the cache.
>
The principle of locality-of-data (ie. the reason why caches
even work) says that you do ;)
Clearly some things benefit from not going through the cache.
But I don't think we should fundamentally change behaviour of
this *just* because it is worth a percent on kernel compiles.
Also, I think that trends in CPU design (more cache, further
from memory, multiple CPUs & cores) should favour stores
going to cache rather than straight to memory... But I'm
just speculating.
--
SUSE Labs, Novell Inc.
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