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> >It would be possible to cache line optimize the layout of struct dentry >in addition. May be an interesting add-on project for someone... I played with this a few months ago, and sent a preliminary patch to linux-kernel, but in my (fairly brief) testing on a 4-way system I wasn't able to produce a measurable benefit from it. I think part of this may have been due to contention on dcache_lock, so maybe dcache_rcu will help there. The main changes were to bring together all the data needed for checking a non-matching dcache hash entry (modulo hash collisions) into one cacheline, and to separate out the mostly-read-only fields from the change-frequently fields. The original patch is at http://marc.theaimsgroup.com/?l=linux-kernel&m=102650654002932&w=2 >But for lookup walking even one cache line - the one containing d_hash - >should be needed. Unless d_hash is unlucky enough to cross a cache >line for its two members ... but I doubt that. No, but on a 32-byte cache line system, d_parent, d_hash and d_name are all on different cache lines, and they're used when checking each entry. On 64-byte systems, d_parent and d_hash will be on the same line, but d_name is still on a separate line and d_name.hash gets checked before d_parent. So bringing these three fields on to the same cacheline would theoretically be a win. Paul - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/ | ||||||||||||
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