Commit 433b0a12 authored by Ilya Dryomov's avatar Ilya Dryomov
Browse files

libceph: use MSG_SENDPAGE_NOTLAST with ceph_tcp_sendpage() 



Prevent do_tcp_sendpages() from calling tcp_push() (at least) once per
page.  Instead, arrange for tcp_push() to be called (at least) once per
data payload.  This results in more MSS-sized packets and fewer packets
overall (5-10% reduction in my tests with typical OSD request sizes).
See commits 2f533844 ("tcp: allow splice() to build full TSO
packets"), 35f9c09f ("tcp: tcp_sendpages() should call tcp_push()
once") and ae62ca7b ("tcp: fix MSG_SENDPAGE_NOTLAST logic") for
details.

Here is an example of a packet size histogram for 128K OSD requests
(MSS = 1448, top 5):

Before:

     SIZE    COUNT
     1448   777700
      952   127915
     1200    39238
     1219     9806
       21     5675

After:

     SIZE    COUNT
     1448   897280
       21     6201
     1019     2797
      643     2739
      376     2479

We could do slightly better by explicitly corking the socket but it's
not clear it's worth it.

Signed-off-by: default avatarIlya Dryomov <idryomov@gmail.com>
parent 3239eb52

net/ceph/messenger.c

+13 −4
Original line number Diff line number Diff line
@@ -560,12 +560,15 @@ static int ceph_tcp_sendmsg(struct socket *sock, struct kvec *iov, 
	return r;

}



/*

 * @more: either or both of MSG_MORE and MSG_SENDPAGE_NOTLAST

 */

static int ceph_tcp_sendpage(struct socket *sock, struct page *page,

		     int offset, size_t size, bool more)

			     int offset, size_t size, int more)

{

	ssize_t (*sendpage)(struct socket *sock, struct page *page,

			    int offset, size_t size, int flags);

	int flags = MSG_DONTWAIT | MSG_NOSIGNAL | (more ? MSG_MORE : 0);

	int flags = MSG_DONTWAIT | MSG_NOSIGNAL | more;

	int ret;



	/*
@@ -1552,6 +1555,7 @@ static int write_partial_message_data(struct ceph_connection *con) 
	struct ceph_msg *msg = con->out_msg;

	struct ceph_msg_data_cursor *cursor = &msg->cursor;

	bool do_datacrc = !ceph_test_opt(from_msgr(con->msgr), NOCRC);

	int more = MSG_MORE | MSG_SENDPAGE_NOTLAST;

	u32 crc;



	dout("%s %p msg %p\n", __func__, con, msg);
@@ -1580,8 +1584,10 @@ static int write_partial_message_data(struct ceph_connection *con) 
		}



		page = ceph_msg_data_next(cursor, &page_offset, &length, NULL);

		if (length == cursor->total_resid)

			more = MSG_MORE;

		ret = ceph_tcp_sendpage(con->sock, page, page_offset, length,

					true);

					more);

		if (ret <= 0) {

			if (do_datacrc)

				msg->footer.data_crc = cpu_to_le32(crc);
@@ -1611,13 +1617,16 @@ static int write_partial_message_data(struct ceph_connection *con) 
 */

static int write_partial_skip(struct ceph_connection *con)

{

	int more = MSG_MORE | MSG_SENDPAGE_NOTLAST;

	int ret;



	dout("%s %p %d left\n", __func__, con, con->out_skip);

	while (con->out_skip > 0) {

		size_t size = min(con->out_skip, (int) PAGE_SIZE);



		ret = ceph_tcp_sendpage(con->sock, zero_page, 0, size, true);

		if (size == con->out_skip)

			more = MSG_MORE;

		ret = ceph_tcp_sendpage(con->sock, zero_page, 0, size, more);

		if (ret <= 0)

			goto out;

		con->out_skip -= ret;

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