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    SubjectRe: "Colo[u]rs"
    Robert Love <rml@tech9.net> wrote:
    > On Mon, 2001-12-10 at 03:00, Stevie O wrote:
    >
    > > For the n-way associative deal:
    >
    > If the cache is n-way associative, it can store n lines at each
    > mapping. So even though two virtual addresses map to the same cache
    > line, they can both be stored. Of course, if you have k addresses such
    > that k>n, then you reach the same problem as direct map (the case where
    > n=1) caches.

    That is a good explanation. Related would be the TLB and its
    thrashing...

    > To reiterate, the point of coloring would be to prevent the case of
    > multiple addresses mapping to the same line.

    Can you get colo[u]red memory from user-space? This would be really
    useful for certain memory intensive applications (I'm thinking of
    large FFT users like mprime/ARMprime here)

    --
    Nick Craig-Wood
    ncw@axis.demon.co.uk

    > Let me give you a
    > real-life example. We recently have been trying to color the kernel
    > stack. If every process's stack lies at the same address (let alone the
    > same page multiple and offset), then they all map to the same place in
    > the cache and we can effectively only cache one of them (and
    > subsequently cache miss on every other access). If we "color" the
    > location of the stack, we make sure they don't all map to the same
    > place. This obviously involves some knowledge of the cache system, but
    > it tends to be general enough that we can get it right for all cases.
    >
    > If you are _really_ interested in this, an excellent and very thorough
    > book is UNIX Systems for Modern Architectures: Symmetric Multiprocessing
    > and Caching for Kernel Programmers, by Curt Schimmel.
    >
    > Robert Love
    >
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