From: Eric Dumazet Date: Wed, 25 Apr 2012 02:12:06 +0000 (-0400) Subject: tcp: allow splice() to build full TSO packets X-Git-Tag: v2.6.32.61~29 X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=2ed8840ba140a6c4c50f32521a3f551be20d9883;p=people%2Fms%2Flinux.git tcp: allow splice() to build full TSO packets [ 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 Signed-off-by: Willy Tarreau --- diff --git a/fs/splice.c b/fs/splice.c index bb92b7c5cdcb..f5d5a2b98563 100644 --- a/fs/splice.c +++ b/fs/splice.c @@ -30,6 +30,7 @@ #include #include #include +#include /* * Attempt to steal a page from a pipe buffer. This should perhaps go into @@ -637,7 +638,9 @@ static int pipe_to_sendpage(struct pipe_inode_info *pipe, ret = buf->ops->confirm(pipe, buf); if (!ret) { - 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; if (file->f_op && file->f_op->sendpage) ret = file->f_op->sendpage(file, buf->page, buf->offset, sd->len, &pos, more); diff --git a/include/linux/socket.h b/include/linux/socket.h index 3273a0c5043b..3124c518d047 100644 --- a/include/linux/socket.h +++ b/include/linux/socket.h @@ -246,7 +246,7 @@ struct ucred { #define MSG_ERRQUEUE 0x2000 /* Fetch message from error queue */ #define MSG_NOSIGNAL 0x4000 /* Do not generate SIGPIPE */ #define MSG_MORE 0x8000 /* Sender will send more */ - +#define MSG_SENDPAGE_NOTLAST 0x20000 /* sendpage() internal : not the last page */ #define MSG_EOF MSG_FIN #define MSG_CMSG_CLOEXEC 0x40000000 /* Set close_on_exit for file diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c index b9644d826653..6232462ffcb8 100644 --- a/net/ipv4/tcp.c +++ b/net/ipv4/tcp.c @@ -847,7 +847,7 @@ wait_for_memory: } out: - if (copied) + if (copied && !(flags & MSG_SENDPAGE_NOTLAST)) tcp_push(sk, flags, mss_now, tp->nonagle); return copied; diff --git a/net/socket.c b/net/socket.c index d449812d6208..bf9fc68a554c 100644 --- a/net/socket.c +++ b/net/socket.c @@ -732,9 +732,9 @@ static ssize_t sock_sendpage(struct file *file, struct page *page, sock = file->private_data; - flags = !(file->f_flags & O_NONBLOCK) ? 0 : MSG_DONTWAIT; - if (more) - flags |= MSG_MORE; + flags = (file->f_flags & O_NONBLOCK) ? MSG_DONTWAIT : 0; + /* more is a combination of MSG_MORE and MSG_SENDPAGE_NOTLAST */ + flags |= more; return kernel_sendpage(sock, page, offset, size, flags); }