Re: maximum buffer size for splice(2) tcp->pipe?

Volker Lendecke
2009-01-14T09:58:43Z

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On Wed, Jan 14, 2009 at 10:13:34AM +0100, Eric Dumazet wrote:
> for (;;) {
> struct pollfd pfd;
> pfd.fd = socket;
> pfd.events = POLLIN;
> if (poll(&pfd, 1, -1) != 1)
> continue;
> res = splice(socket, NULL, pipefds[1], NULL, 65536, SPLICE_F_MOVE|SPLICE_F_NONBLOCK);
> if (res > 0)
> nwritten = splice(pipefds[0], NULL, file_fd, NULL, res, SPLICE_F_MOVE|SPLICE_F_MORE);
> }

Doesn't this reduce performance again? I thought the whole
point of splice() was to increase performance by avoiding
memory copies. If I have to do a poll syscall for each call
to splice, doesn't the context switch eat that performance
advantage again?

Or was splice designed only for multi-threaded applications
(which at least Samba is not)?

Volker

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