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Mon, 09 Nov 2020 17:36:17 +0000 Received: from pps.filterd (aserp3030.oracle.com [127.0.0.1]) by aserp3030.oracle.com (8.16.0.42/8.16.0.42) with SMTP id 0A9HV9WX042425; Mon, 9 Nov 2020 17:36:17 GMT Received: from aserv0121.oracle.com (aserv0121.oracle.com [141.146.126.235]) by aserp3030.oracle.com with ESMTP id 34p55m81pg-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Mon, 09 Nov 2020 17:36:16 +0000 Received: from abhmp0013.oracle.com (abhmp0013.oracle.com [141.146.116.19]) by aserv0121.oracle.com (8.14.4/8.13.8) with ESMTP id 0A9HaGgN028117; Mon, 9 Nov 2020 17:36:16 GMT Received: from anon-dhcp-152.1015granger.net (/68.61.232.219) by default (Oracle Beehive Gateway v4.0) with ESMTP ; Mon, 09 Nov 2020 09:36:16 -0800 Content-Type: text/plain; charset=us-ascii Mime-Version: 1.0 (Mac OS X Mail 13.4 \(3608.120.23.2.4\)) Subject: Re: [PATCH RFC] SUNRPC: Use zero-copy to perform socket send operations From: Chuck Lever In-Reply-To: Date: Mon, 9 Nov 2020 12:36:15 -0500 Cc: Linux NFS Mailing List , "netdev@vger.kernel.org" Content-Transfer-Encoding: quoted-printable Message-Id: <5056C7C7-7B26-4667-9691-D2F634C02FB1@oracle.com> References: <160493771006.15633.8524084764848931537.stgit@klimt.1015granger.net> <9ce015245c916b2c90de72440a22f801142f2c6e.camel@hammerspace.com> <0313136F-6801-434F-8304-72B9EADD389E@oracle.com> To: Trond Myklebust X-Mailer: Apple Mail (2.3608.120.23.2.4) X-Proofpoint-Virus-Version: vendor=nai engine=6000 definitions=9800 signatures=668682 X-Proofpoint-Spam-Details: rule=notspam policy=default score=0 adultscore=0 spamscore=0 phishscore=0 mlxlogscore=999 mlxscore=0 malwarescore=0 bulkscore=0 suspectscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2009150000 definitions=main-2011090121 X-Proofpoint-Virus-Version: vendor=nai engine=6000 definitions=9800 signatures=668682 X-Proofpoint-Spam-Details: rule=notspam policy=default score=0 lowpriorityscore=0 priorityscore=1501 clxscore=1015 malwarescore=0 mlxscore=0 spamscore=0 suspectscore=0 mlxlogscore=999 impostorscore=0 phishscore=0 adultscore=0 bulkscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2009150000 definitions=main-2011090121 Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org > On Nov 9, 2020, at 12:32 PM, Trond Myklebust = wrote: >=20 > On Mon, 2020-11-09 at 12:12 -0500, Chuck Lever wrote: >>=20 >>=20 >>> On Nov 9, 2020, at 12:08 PM, Trond Myklebust >>> wrote: >>>=20 >>> On Mon, 2020-11-09 at 11:03 -0500, Chuck Lever wrote: >>>> 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. >>>>=20 >>>> Investigation showed that tcp_sendmsg() was not using zero-copy >>>> to >>>> send the xdr_buf's bvec pages, but instead was relying on memcpy. >>>>=20 >>>> Set up the socket and each msghdr that bears bvec pages to use >>>> the >>>> zero-copy mechanism in tcp_sendmsg. >>>>=20 >>>> Reported-by: Daire Byrne >>>> BugLink: https://bugzilla.kernel.org/show_bug.cgi?id=3D209439 >>>> Fixes: da1661b93bf4 ("SUNRPC: Teach server to use >>>> xprt_sock_sendmsg >>>> for socket sends") >>>> Signed-off-by: Chuck Lever >>>> --- >>>> net/sunrpc/socklib.c | 5 ++++- >>>> net/sunrpc/svcsock.c | 1 + >>>> net/sunrpc/xprtsock.c | 1 + >>>> 3 files changed, 6 insertions(+), 1 deletion(-) >>>>=20 >>>> 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. >>>>=20 >>>>=20 >>>> 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; >>>> =20 >>>> + msg->msg_flags |=3D 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 =3D xprt_sendmsg(sock, msg, base + xdr->page_base); >>>> + msg->msg_flags &=3D ~MSG_ZEROCOPY; >>>> + return err; >>>> } >>>> =20 >>>> /* 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 =3D 0; >>>> memset(&svsk->sk_pages[0], 0, sizeof(svsk- >>>>> sk_pages)); >>>> =20 >>>> + sock_set_flag(sk, SOCK_ZEROCOPY); >>>> tcp_sk(sk)->nonagle |=3D TCP_NAGLE_OFF; >>>> =20 >>>> 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) >>>> =20 >>>> /* socket options */ >>>> sock_reset_flag(sk, SOCK_LINGER); >>>> + sock_set_flag(sk, SOCK_ZEROCOPY); >>>> tcp_sk(sk)->nonagle |=3D TCP_NAGLE_OFF; >>>> =20 >>>> xprt_clear_connected(xprt); >>>>=20 >>>>=20 >>> I'm thinking we are not really allowed to do that here. The pages >>> we >>> pass in to the RPC layer are not guaranteed to contain stable data >>> since they include unlocked page cache pages as well as O_DIRECT >>> pages. >>=20 >> I assume you mean the client side only. Those issues aren't a factor >> on the server. Not setting SOCK_ZEROCOPY here should be enough to >> prevent the use of zero-copy on the client. >>=20 >> However, the client loses the benefits of sending a page at a time. >> Is there a desire to remedy that somehow? >=20 > What about splice reads on the server side? On the server, this path formerly used kernel_sendpages(), which I assumed is similar to the sendmsg zero-copy mechanism. How does kernel_sendpages() mitigate against page instability? -- Chuck Lever