Messages in this thread |  | | Date | Mon, 18 Sep 2000 08:38:56 -0700 (PDT) | From | Matthew Jacob <> |
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> > 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
Yup. That's true. Like it's also nonintuitive sometimes that PIO can even beat, in some cases, DMA (some graphics fifo devices, e.g.).
> > > 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.
What was the CPU utilization?
-matt
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