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    SubjectRe: [PATCH] mm/slab.c : prefetchw the start of new allocated objects
    From: Eric Dumazet <>
    Date: Fri, 29 Jul 2005 11:05:09 +0200

    > Some CPU lacks a prefetchw() and currently do nothing, so I ask this
    > question : Should'nt make prefetchw() do at least a prefetch() ? A
    > read hint is better than nothing.

    This is not true, especially on SMP. If the only prefetch variant
    available does a "prefetch for read", the cpu will only grab the
    cacheline in shared state if other cpus have a dirty copy.

    And, as a result, when the write to the cache line occurs yet
    another bus transaction will go out in order to get exclusive
    access to the cache line on the local cpu. This is extremely

    So it's better in this case to make no prefetch, and thus only
    incur one bus transaction when the memory access occurs.
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