> When transferring one or more pages via a page-alligned
> buffer and normal read() or write(), VM tricks will be
> used to avoid copying the data. If you touch the page
You mean mmap(). You can do that already but it isnt the win you might
think. In fact for some operations mmap is slower just due to the mmu bashing
overhead and TLB misses.
Its non intuitive that mmu operations cost more than a bulk copy but its
frequently the case. sendfile() works nicely because it is working on data
that isnt user mapped. O_DIRECT raw I/O has overheads too and its not clear
where the break even points are
> They've gotten 960 megabits/sec out of a gigabit Ethernet card
> with this. Not stable yet.
I think Jes was getting this in Linux TCP/IP without zero copy.
Alan
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