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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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