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    SubjectRe: touch_cache() only touches two thirds
    Date

    > The corrected code in <http://bugzilla.kernel.org/show_bug.cgi?id=7476#c4>
    > covers the full cache range. Granted that modern CPUs may be able to track
    > multiple simultaneous cache access streams: how many such streams are they
    > likely to be able to follow at once? It seems like going from 1 to 2 would
    > be a big win, 2 to 3 a small win, beyond that it wouldn't likely make much
    > incremental difference. So what do the actual implementations in the field
    > support?

    I remember reading at some point that a POWER4 could track at least 5+ parallel
    streams. I don't know how many K8 handles, but it is multiple too at least
    (forward and backwards)

    I don't have more data, but at least the newer Intel CPUs seem to be also
    very good at prefetching and when you look at a die photo the L/S unit
    in general is quite big. More than 6 streams handled is certainly a
    possibility.

    I guess it could be figured out with some clever benchmarking.
    >
    > The code (original and corrected) uses 6 simultaneous streams.

    My gut feeling is that this is not enough.

    > I have a modified version that takes a `ways' parameter to use an arbitrary
    > number of streams. I'll post that onto bugzilla.kernel.org.

    Post it to the list please.

    -Andi

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