Andrew Gallatin writes:
> It has been a while since I've had a zero-copy FS to play with. I can
> tell you that with the 10GbE nic I do drivers for, the CPU overhead
> drops by 50-60% when you skip the copy on socket writes from userspace
> (sendfile vs write) on both opteron and T2000. This translates to
> more than doubling the single stream bandwidth on anemic CPUs (like a
> single core on a T2000).
Doing zero-copy from user space to kernel means flipping page table
entries. When we've looked into this in the recent past, we've[1]
found that the cost of doing this completely dwarfs the cost of
copying the data on fairly modern architectures.
I don't know if that's still true. Perhaps it's something to put on
the VM wish list: "can we flip pages, or are we still stuck there?"
[1] royal "we:" I didn't do that benchmarking, but I hope those who
did will eventually comment. ;-}
--
James Carlson, KISS Network <[EMAIL PROTECTED]>
Sun Microsystems / 1 Network Drive 71.232W Vox +1 781 442 2084
MS UBUR02-212 / Burlington MA 01803-2757 42.496N Fax +1 781 442 1677
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