Messages in this thread | | | Date | Sat, 10 Nov 2001 16:20:06 +1100 | From | Anton Blanchard <> | Subject | Re: speed difference between using hard-linked and modular drives? |
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Hi,
> It _IS_ a big deal. Fetching _ONE_ hash chain cache line > is always going to be cheaper than fetching _FIVE_ to _TEN_ > page struct cache lines while walking the list.
Exactly, the reason I found the pagecache hash was too small was because __find_page_nolock was one of the worst offenders when doing zero copy web serving of a large dataset.
> Even if prefetch would kill all of this overhead (sorry, it won't), it > is _DUMB_ and _STUPID_ to bring those _FIVE_ to _TEN_ cache lines into > the processor just to lookup _ONE_ page.
Yes you cant expect prefetch to help you when you use the data 10 instructions after you issue the prefetch. (ie walking the hash chain)
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