Re: [PATCH] SUNRPC: Use TCP_CORK to optimise send performance on the server

[Chuck Lever <chuck.lever@oracle.com>]

Hey Trond-

> On Feb 13, 2021, at 3:25 PM, trondmy@kernel.org wrote:
> 
> From: Trond Myklebust <trond.myklebust@hammerspace.com>
> 
> Use a counter to keep track of how many requests are queued behind the
> xprt->xpt_mutex, and keep TCP_CORK set until the queue is empty.
> 
> Signed-off-by: Trond Myklebust <trond.myklebust@hammerspace.com>

Let's move this forward a little bit.

I'd like to see the previously discussed MSG_MORE simplification
integrated into this patch.

In addition to Daire's testing, I've done some testing:
- No behavior regressions noted
- No changes in large I/O throughput
- Slightly shorter RTTs on software build

And the current version of the patch is now in the for-rc branch
of https://git.kernel.org/pub/scm/linux/kernel/git/cel/linux.git/
to get broader testing exposure.

This work is a candidate for a second NFSD PR during the 5.12
merge window, along with the other patches currently in the
for-rc branch.


> ---
> include/linux/sunrpc/svcsock.h | 2 ++
> net/sunrpc/svcsock.c           | 8 +++++++-
> 2 files changed, 9 insertions(+), 1 deletion(-)
> 
> diff --git a/include/linux/sunrpc/svcsock.h b/include/linux/sunrpc/svcsock.h
> index b7ac7fe68306..bcc555c7ae9c 100644
> --- a/include/linux/sunrpc/svcsock.h
> +++ b/include/linux/sunrpc/svcsock.h
> @@ -35,6 +35,8 @@ struct svc_sock {
> 	/* Total length of the data (not including fragment headers)
> 	 * received so far in the fragments making up this rpc: */
> 	u32			sk_datalen;
> +	/* Number of queued send requests */
> +	atomic_t		sk_sendqlen;
> 
> 	struct page *		sk_pages[RPCSVC_MAXPAGES];	/* received data */
> };
> diff --git a/net/sunrpc/svcsock.c b/net/sunrpc/svcsock.c
> index 5a809c64dc7b..231f510a4830 100644
> --- a/net/sunrpc/svcsock.c
> +++ b/net/sunrpc/svcsock.c
> @@ -1171,18 +1171,23 @@ static int svc_tcp_sendto(struct svc_rqst *rqstp)
> 
> 	svc_tcp_release_rqst(rqstp);
> 
> +	atomic_inc(&svsk->sk_sendqlen);
> 	mutex_lock(&xprt->xpt_mutex);
> 	if (svc_xprt_is_dead(xprt))
> 		goto out_notconn;
> +	tcp_sock_set_cork(svsk->sk_sk, true);
> 	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)))
> 		goto out_close;
> +	if (atomic_dec_and_test(&svsk->sk_sendqlen))
> +		tcp_sock_set_cork(svsk->sk_sk, false);
> 	mutex_unlock(&xprt->xpt_mutex);
> 	return sent;
> 
> out_notconn:
> +	atomic_dec(&svsk->sk_sendqlen);
> 	mutex_unlock(&xprt->xpt_mutex);
> 	return -ENOTCONN;
> out_close:
> @@ -1192,6 +1197,7 @@ static int svc_tcp_sendto(struct svc_rqst *rqstp)
> 		  (err < 0) ? err : sent, xdr->len);
> 	set_bit(XPT_CLOSE, &xprt->xpt_flags);
> 	svc_xprt_enqueue(xprt);
> +	atomic_dec(&svsk->sk_sendqlen);
> 	mutex_unlock(&xprt->xpt_mutex);
> 	return -EAGAIN;
> }
> @@ -1261,7 +1267,7 @@ 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));
> 
> -		tcp_sk(sk)->nonagle |= TCP_NAGLE_OFF;
> +		tcp_sock_set_nodelay(sk);
> 
> 		set_bit(XPT_DATA, &svsk->sk_xprt.xpt_flags);
> 		switch (sk->sk_state) {
> -- 
> 2.29.2
> 

--
Chuck Lever