From 4a85a6a3320b4a622315d2e0ea91a1d2b013bce4 Mon Sep 17 00:00:00 2001 From: Chuck Lever Date: Fri, 18 Dec 2020 12:28:41 -0500 Subject: SUNRPC: Handle TCP socket sends with kernel_sendpage() again 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. This means copying every byte of a large NFS READ payload. It looks like TLS sockets do indeed support a ->sendpage method, so it's really not necessary to use xprt_sock_sendmsg() to support TLS fully on the server. A mechanical reversion of da1661b93bf4 is not possible at this point, but we can re-implement the server's TCP socket sendmsg path using kernel_sendpage(). Reported-by: Daire Byrne BugLink: https://bugzilla.kernel.org/show_bug.cgi?id=209439 Signed-off-by: Chuck Lever --- net/sunrpc/svcsock.c | 86 +++++++++++++++++++++++++++++++++++++++++++++++++++- 1 file changed, 85 insertions(+), 1 deletion(-) (limited to 'net/sunrpc/svcsock.c') diff --git a/net/sunrpc/svcsock.c b/net/sunrpc/svcsock.c index b248f2349437..c9766d07eb81 100644 --- a/net/sunrpc/svcsock.c +++ b/net/sunrpc/svcsock.c @@ -1062,6 +1062,90 @@ err_noclose: return 0; /* record not complete */ } +static int svc_tcp_send_kvec(struct socket *sock, const struct kvec *vec, + int flags) +{ + return kernel_sendpage(sock, virt_to_page(vec->iov_base), + offset_in_page(vec->iov_base), + vec->iov_len, flags); +} + +/* + * kernel_sendpage() is used exclusively to reduce the number of + * copy operations in this path. Therefore the caller must ensure + * that the pages backing @xdr are unchanging. + * + * In addition, the logic assumes that * .bv_len is never larger + * than PAGE_SIZE. + */ +static int svc_tcp_sendmsg(struct socket *sock, struct msghdr *msg, + struct xdr_buf *xdr, rpc_fraghdr marker, + unsigned int *sentp) +{ + const struct kvec *head = xdr->head; + const struct kvec *tail = xdr->tail; + struct kvec rm = { + .iov_base = &marker, + .iov_len = sizeof(marker), + }; + int flags, ret; + + *sentp = 0; + xdr_alloc_bvec(xdr, GFP_KERNEL); + + msg->msg_flags = MSG_MORE; + ret = kernel_sendmsg(sock, msg, &rm, 1, rm.iov_len); + if (ret < 0) + return ret; + *sentp += ret; + if (ret != rm.iov_len) + return -EAGAIN; + + flags = head->iov_len < xdr->len ? MSG_MORE | MSG_SENDPAGE_NOTLAST : 0; + ret = svc_tcp_send_kvec(sock, head, flags); + if (ret < 0) + return ret; + *sentp += ret; + if (ret != head->iov_len) + goto out; + + if (xdr->page_len) { + unsigned int offset, len, remaining; + struct bio_vec *bvec; + + bvec = xdr->bvec; + offset = xdr->page_base; + remaining = xdr->page_len; + flags = MSG_MORE | MSG_SENDPAGE_NOTLAST; + while (remaining > 0) { + if (remaining <= PAGE_SIZE && tail->iov_len == 0) + flags = 0; + len = min(remaining, bvec->bv_len); + ret = kernel_sendpage(sock, bvec->bv_page, + bvec->bv_offset + offset, + len, flags); + if (ret < 0) + return ret; + *sentp += ret; + if (ret != len) + goto out; + remaining -= len; + offset = 0; + bvec++; + } + } + + if (tail->iov_len) { + ret = svc_tcp_send_kvec(sock, tail, 0); + if (ret < 0) + return ret; + *sentp += ret; + } + +out: + return 0; +} + /** * svc_tcp_sendto - Send out a reply on a TCP socket * @rqstp: completed svc_rqst @@ -1089,7 +1173,7 @@ static int svc_tcp_sendto(struct svc_rqst *rqstp) mutex_lock(&xprt->xpt_mutex); if (svc_xprt_is_dead(xprt)) goto out_notconn; - err = xprt_sock_sendmsg(svsk->sk_sock, &msg, xdr, 0, marker, &sent); + err = svc_tcp_sendmsg(svsk->sk_sock, &msg, xdr, marker, &sent); xdr_free_bvec(xdr); trace_svcsock_tcp_send(xprt, err < 0 ? err : sent); if (err < 0 || sent != (xdr->len + sizeof(marker))) -- cgit v1.2.3