From: Eric Dumazet <[EMAIL PROTECTED]> 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 inefficient. So it's better in this case to make no prefetch, and thus only incur one bus transaction when the memory access occurs. - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
