From 8d2228dd95c656e5fc9af2e8776f9c95e269806f Mon Sep 17 00:00:00 2001 From: Eric Dumazet Date: Tue, 24 Apr 2012 22:12:06 -0400 Subject: tcp: allow splice() to build full TSO packets MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit [ This combines upstream commit 2f53384424251c06038ae612e56231b96ab610ee and the follow-on bug fix commit 35f9c09fe9c72eb8ca2b8e89a593e1c151f28fc2 ] vmsplice()/splice(pipe, socket) call do_tcp_sendpages() one page at a time, adding at most 4096 bytes to an skb. (assuming PAGE_SIZE=4096) The call to tcp_push() at the end of do_tcp_sendpages() forces an immediate xmit when pipe is not already filled, and tso_fragment() try to split these skb to MSS multiples. 4096 bytes are usually split in a skb with 2 MSS, and a remaining sub-mss skb (assuming MTU=1500) This makes slow start suboptimal because many small frames are sent to qdisc/driver layers instead of big ones (constrained by cwnd and packets in flight of course) In fact, applications using sendmsg() (adding an additional memory copy) instead of vmsplice()/splice()/sendfile() are a bit faster because of this anomaly, especially if serving small files in environments with large initial [c]wnd. Call tcp_push() only if MSG_MORE is not set in the flags parameter. This bit is automatically provided by splice() internals but for the last page, or on all pages if user specified SPLICE_F_MORE splice() flag. In some workloads, this can reduce number of sent logical packets by an order of magnitude, making zero-copy TCP actually faster than one-copy :) Reported-by: Tom Herbert Cc: Nandita Dukkipati Cc: Neal Cardwell Cc: Tom Herbert Cc: Yuchung Cheng Cc: H.K. Jerry Chu Cc: Maciej Żenczykowski Cc: Mahesh Bandewar Cc: Ilpo Järvinen Signed-off-by: Eric Dumazet Signed-off-by: David S. Miller Signed-off-by: Greg Kroah-Hartman --- fs/splice.c | 5 ++++- 1 file changed, 4 insertions(+), 1 deletion(-) (limited to 'fs/splice.c') diff --git a/fs/splice.c b/fs/splice.c index aa866d3..9d89008 100644 --- a/fs/splice.c +++ b/fs/splice.c @@ -31,6 +31,7 @@ #include #include #include +#include /* * Attempt to steal a page from a pipe buffer. This should perhaps go into @@ -691,7 +692,9 @@ static int pipe_to_sendpage(struct pipe_inode_info *pipe, if (!likely(file->f_op && file->f_op->sendpage)) return -EINVAL; - more = (sd->flags & SPLICE_F_MORE) || sd->len < sd->total_len; + more = (sd->flags & SPLICE_F_MORE) ? MSG_MORE : 0; + if (sd->len < sd->total_len) + more |= MSG_SENDPAGE_NOTLAST; return file->f_op->sendpage(file, buf->page, buf->offset, sd->len, &pos, more); } -- cgit v1.1