Daire Byrne reports a ~50% aggregrate throughput regression on his
Linux NFS server after commit da1661b93bf4 ("SUNRPC: Teach server to
use xprt_sock_sendmsg for socket sends"), which replaced
kernel_send_page() calls in NFSD's socket send path with calls to
sock_sendmsg() using iov_iter.Investigation showed that tcp_sendmsg() was not using zero-copy to send the xdr_buf's bvec pages, but instead was relying on memcpy. Set up the socket and each msghdr that bears bvec pages to use the zero-copy mechanism in tcp_sendmsg. Reported-by: Daire Byrne <da...@dneg.com> BugLink: https://bugzilla.kernel.org/show_bug.cgi?id=209439 Fixes: da1661b93bf4 ("SUNRPC: Teach server to use xprt_sock_sendmsg for socket sends") Signed-off-by: Chuck Lever <chuck.le...@oracle.com> --- net/sunrpc/socklib.c | 5 ++++- net/sunrpc/svcsock.c | 1 + net/sunrpc/xprtsock.c | 1 + 3 files changed, 6 insertions(+), 1 deletion(-) This patch does not fully resolve the issue. Daire reports high softIRQ activity after the patch is applied, and this activity seems to prevent full restoration of previous performance. diff --git a/net/sunrpc/socklib.c b/net/sunrpc/socklib.c index d52313af82bc..af47596a7bdd 100644 --- a/net/sunrpc/socklib.c +++ b/net/sunrpc/socklib.c @@ -226,9 +226,12 @@ static int xprt_send_pagedata(struct socket *sock, struct msghdr *msg, if (err < 0) return err; + msg->msg_flags |= MSG_ZEROCOPY; iov_iter_bvec(&msg->msg_iter, WRITE, xdr->bvec, xdr_buf_pagecount(xdr), xdr->page_len + xdr->page_base); - return xprt_sendmsg(sock, msg, base + xdr->page_base); + err = xprt_sendmsg(sock, msg, base + xdr->page_base); + msg->msg_flags &= ~MSG_ZEROCOPY; + return err; } /* Common case: diff --git a/net/sunrpc/svcsock.c b/net/sunrpc/svcsock.c index c2752e2b9ce3..c814b4953b15 100644 --- a/net/sunrpc/svcsock.c +++ b/net/sunrpc/svcsock.c @@ -1176,6 +1176,7 @@ static void svc_tcp_init(struct svc_sock *svsk, struct svc_serv *serv) svsk->sk_datalen = 0; memset(&svsk->sk_pages[0], 0, sizeof(svsk->sk_pages)); + sock_set_flag(sk, SOCK_ZEROCOPY); tcp_sk(sk)->nonagle |= TCP_NAGLE_OFF; set_bit(XPT_DATA, &svsk->sk_xprt.xpt_flags); diff --git a/net/sunrpc/xprtsock.c b/net/sunrpc/xprtsock.c index 7090bbee0ec5..343c6396b297 100644 --- a/net/sunrpc/xprtsock.c +++ b/net/sunrpc/xprtsock.c @@ -2175,6 +2175,7 @@ static int xs_tcp_finish_connecting(struct rpc_xprt *xprt, struct socket *sock) /* socket options */ sock_reset_flag(sk, SOCK_LINGER); + sock_set_flag(sk, SOCK_ZEROCOPY); tcp_sk(sk)->nonagle |= TCP_NAGLE_OFF; xprt_clear_connected(xprt);
