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

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

> On Feb 16, 2021, at 12:10 PM, Trond Myklebust <trondmy@hammerspace.com> wrote:
> 
> On Tue, 2021-02-16 at 16:27 +0000, Chuck Lever wrote:
>> 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.
>> 
> 
> Hmm... I think I'd prefer to make it incremental to this one. I wasn't
> too sure about whether or not removing MSG_SENDPAGE_NOTLAST makes a
> difference.
> AFAICS, the answer is no, but just in case, let's make it easy to back
> this change out.

OK. Please send an incremental patch. Thanks!


>> 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
>> 
>> 
>> 
> 
> -- 
> Trond Myklebust
> CTO, Hammerspace Inc
> 4984 El Camino Real, Suite 208
> Los Altos, CA 94022
> ​
> www.hammer.space

--
Chuck Lever