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


    On Sat, 28 Feb 2009, Arjan van de Ven wrote:
    >
    > it invalidates all caches in the hierarchy

    Yeah, now that I look at the intel pdf's, I see that.

    > afaik this is what Intel cpus do; but I also thought this behavior was
    > quite architectural as well...

    Ok, I really think we should definitely not use non-temporal stores for
    anything smaller than one full page in that case. In fact, I wonder if
    even any of the old streaming benchmarks are even true. I thought it would
    still stay in the L3, but yes, it literally seems to make the access
    totally noncached and WC.

    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.

    Linus


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