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SubjectRe: PATCH: Raw device IO for 2.1.131
Jes Sorensen writes:
> >>>>> "Richard" == Richard Gooch <rgooch@atnf.csiro.au> writes:
>
> Richard> Jes Sorensen writes:
> >> SGI managed to get zero copy right for write() on a socket and it
> >> works great, I'd love having Linux do the same.
>
> Richard> To get you what you want without resorting to sendfile(),
> Richard> we'd have to be able to be able to pin down user pages and
> Richard> then initiate DMA. Linus has said he doesn't like that idea
> Richard> and has also pointed out he feels that the copy operation
> Richard> would not be a significant overhead. Other have mentioned
> Richard> other applications (video capture and processing) where they
> Richard> feel an extra copy *is* significant. But is this the case
> Richard> with your application? It seems to me that if you have a
> Richard> bunch of user pages you want to DMA out, you have already
> Richard> spent a considerable amount of time generating the data, so
> Richard> an extra copy is not significant. Is that so?
>
> No most of our applications do read(filefd), write(sockfd) and as
> such it could probably be done with sendfile, the main issue is that
> it requires rewriting the code as a special case for Linux.

How about mmap(filefd); write (sockfd, mmap_addr); ?

Regards,

Richard....
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