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libceph: use MSG_SENDPAGE_NOTLAST with ceph_tcp_sendpage()

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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 2f53384424 ("tcp: allow splice() to build full TSO
packets"), 35f9c09fe9 ("tcp: tcp_sendpages() should call tcp_push()
once") and ae62ca7b03 ("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: Ilya Dryomov <idryomov@gmail.com>
This commit is contained in:
Ilya Dryomov 2018-11-20 15:44:00 +01:00
parent 3239eb5215
commit 433b0a1295
1 changed files with 13 additions and 4 deletions
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17
net/ceph/messenger.c
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@ -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;