Linux-kernel mailing list archive 1998-50,: Re: PATCH: Raw device IO for 2.1.131

# Re: PATCH: Raw device IO for 2.1.131

Jes Sorensen (Jes.Sorensen@cern.ch)
14 Dec 1998 11:10:14 +0100

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>>>>> "Richard" == Richard Gooch <rgooch@atnf.csiro.au> writes:

Richard> pmonta@halibut.imedia.com writes:
>> With a fast disk array it's easy to make this wastage dominate the
>> CPU. You remark that this is an evil oddity; I'm not sure I agree.
>> Fast I/O buses are nice. I'd *like* to be I/O bound, but it's not
>> in the cards with vanilla Linux because the CPU is forced to be
>> involved, to no benefit that I can see.

Richard> But isn't this where sendfile(2) is used? The input file is
Richard> your disc file and the output file is your network
Richard> socket. The kernel triggers the DMA from disc to memory (say
Richard> a skbuf) and then triggers the DMA from memory to the network
Richard> interface. No cache pollution at all.

Let me point out why I don't like sendfile() then. Most operating
systems don't support sendfile() and as such it is a pain in the neck
to have to write multiple versions of your software if you run on
multiple operating systems. Ie. the software we use here for most of
out data transfers is used on at least six different UNIX versions in
house and I bet some of the other sites using this software might run
it on other flavors.

SGI managed to get zero copy right for write() on a socket and it
works great, I'd love having Linux do the same.

Jes

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