Messages in this thread |  | | Date | Mon, 10 Sep 2001 22:23:13 +0100 | From | Alex Bligh - linux-kernel <> | Subject | Re: linux-2.4.10-pre5 |
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--On Monday, 10 September, 2001 11:18 PM +0200 Daniel Phillips <phillips@bonn-fries.net> wrote:
> We lost 78.5 seconds somewhere. From the sound of the disk drives, I'd > say we lost it to seeking, which physical readahead with a large cache > would be able to largely eliminate in this case.
So you only get a large % of your 78.5 seconds back from pure physical readahead if the files and metadata are (a) ordered in monitonically increasing disk locations w.r.t. access order, and (b) physically close (no time wasted reading in irrelevant data), or you apply some form of clairvoyance patch :-) An alternative benchmark would be do dd the /entire/ disk into RAM, then run your diff on that, and I bet you get the opposite result.
More serious point: if we retain readahead at a logical level, you get it for non-physical files too (e.g. NFS) - I presume this is the intention. If so, what advantage does additional physical readahead give you, given physical ordering is surely no better (and probably worse than) logical ordering.
-- Alex Bligh - 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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