Re: [patch] x86, mm: pass in 'total' to __copy_from_user_*nocache()

[Arjan van de Ven]

On Sat, 28 Feb 2009 09:42:18 -0800 (PST)
Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx> wrote:

> 
> That's almost unacceptable in the long run. With a 8MB L3 cache - and
> a compile sequence, do we really want to go out to memory to write
> the .S file, and then have the assembler go out to memory to read it
> back? For a compile, that _probably_ is all fine (the compiler in
> particular will have enough data structures around that it's not
> going to fit in the cache anyway), but I'm seeing leaner compilers
> and other cases where forcing things out all the way on the bus is
> simply the wrong thing.

non-temporal is almost always wrong

one of the valid cases is where you KNOW you'll be doing dma for all of
the memory very shortly (say, an O_SYNC/O_DIRECT write of 4Kb) since
that would tend to evict it from cache anyway.

but beyond that... not so much.

-- 
Arjan van de Ven 	Intel Open Source Technology Centre
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