Re: [PATCH 2/2] sunrpc: socket buffer size module parameter

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

On 02/22/2010 01:54 PM, Ben Myers wrote:
> At 1020 threads the send buffer size wraps and becomes negative causing the nfs
> server to grind to a halt.  Rather than setting bufsize based upon the number
> of nfsd threads I have made the buffer sizes tuneable via module parameters.
> In other versions of this patch they were sysctls.
>
> Set the buffer sizes in terms of the number of rpcs you want to fit into the
> buffer.
>
> Signed-off-by: Ben Myers<bpm@sgi.com>
> ---
>   fs/nfsd/nfsctl.c         |    1 +
>   net/sunrpc/sunrpc_syms.c |   39 ++++++++++++++++++++++
>   net/sunrpc/svcsock.c     |   81 +++++++++++++++++++++++-----------------------
>   3 files changed, 80 insertions(+), 41 deletions(-)
>
> diff --git a/fs/nfsd/nfsctl.c b/fs/nfsd/nfsctl.c
> index 981366d..bce8df3 100644
> --- a/fs/nfsd/nfsctl.c
> +++ b/fs/nfsd/nfsctl.c
> @@ -19,6 +19,7 @@
>   /* Default to use existing settings in svc_check_conn_limits */
>   unsigned int nfsd_max_connections = 0;
>
> +
>   /*
>    *	We have a single directory with 9 nodes in it.
>    */
> diff --git a/net/sunrpc/sunrpc_syms.c b/net/sunrpc/sunrpc_syms.c
> index f438347..a7a80b4 100644
> --- a/net/sunrpc/sunrpc_syms.c
> +++ b/net/sunrpc/sunrpc_syms.c
> @@ -26,6 +26,45 @@ extern struct cache_detail ip_map_cache, unix_gid_cache;
>
>   extern void cleanup_rpcb_clnt(void);
>
> +/*
> + * Size each socket's send and receive buffers based upon the number of rpcs
> + * we'd like to be able to fit into them.  The TCP rcvbuf is enough for just a
> + * few requests.  TCP sndbuf is the same as the tcp_slot_table_entries default,
> + * the maximum number of in-flight rpcs for a client.  UDP sndbuf and rcvbuf
> + * defaults are the same as the udp_slot_table_entries default.
> + *
> + * Setting these too small can cause nfsd threads to block when sending.
> + */
> +int            tcp_rcvbuf_nrpc = 6;

Just curious, is this '6' a typo?  Perhaps it would be nice to have a 
single macro defined as the default value for all of these.

Do we have a high degree of confidence that these new default settings 
will not adversely affect workloads that already perform well?

> +int            tcp_sndbuf_nrpc = 16;
> +
> +int            udp_rcvbuf_nrpc = 16;
> +int            udp_sndbuf_nrpc = 16;
> +
> +/*
> + * Minimum for bufsize settings is enough space for 6 rpcs, maximum is enough
> + * space for 128 rpcs.
> + */
> +static int param_set_bufsize_nrpc(const char *val, struct kernel_param *kp)
> +{
> +	char	*endp;
> +	int 	num = simple_strtol(val,&endp, 0);
> +
> +	if (endp == val || (*endp&&  *endp != '\n') || num<  6 || num>  128)
> +		return -EINVAL;
> +	*((int *)kp->arg) = num;
> +	return 0;
> +}
> +
> +module_param_call(tcp_rcvbuf_nrpc, param_set_bufsize_nrpc, param_get_int,
> +	&tcp_rcvbuf_nrpc, 0644);
> +module_param_call(tcp_sndbuf_nrpc, param_set_bufsize_nrpc, param_get_int,
> +		&tcp_sndbuf_nrpc, 0644);
> +module_param_call(udp_rcvbuf_nrpc, param_set_bufsize_nrpc, param_get_int,
> +	&udp_rcvbuf_nrpc, 0644);
> +module_param_call(udp_sndbuf_nrpc, param_set_bufsize_nrpc, param_get_int,
> +	&udp_sndbuf_nrpc, 0644);
> +
>   static int __init
>   init_sunrpc(void)
>   {
> diff --git a/net/sunrpc/svcsock.c b/net/sunrpc/svcsock.c
> index 9e09391..f172b27 100644
> --- a/net/sunrpc/svcsock.c
> +++ b/net/sunrpc/svcsock.c
> @@ -381,8 +381,7 @@ static int svc_recvfrom(struct svc_rqst *rqstp, struct kvec *iov, int nr,
>   /*
>    * Set socket snd and rcv buffer lengths
>    */
> -static void svc_sock_setbufsize(struct socket *sock, unsigned int snd,
> -				unsigned int rcv)
> +static void svc_sock_setbufsize(struct socket *sock, int snd, int rcv)
>   {
>   #if 0
>   	mm_segment_t	oldfs;
> @@ -398,13 +397,14 @@ static void svc_sock_setbufsize(struct socket *sock, unsigned int snd,
>   	 * DaveM said I could!
>   	 */
>   	lock_sock(sock->sk);
> -	sock->sk->sk_sndbuf = snd * 2;
> -	sock->sk->sk_rcvbuf = rcv * 2;
> +	sock->sk->sk_sndbuf = snd;
> +	sock->sk->sk_rcvbuf = rcv;
>   	sock->sk->sk_userlocks |= SOCK_SNDBUF_LOCK|SOCK_RCVBUF_LOCK;
>   	sock->sk->sk_write_space(sock->sk);
>   	release_sock(sock->sk);
>   #endif
>   }
> +
>   /*
>    * INET callback when data has been received on the socket.
>    */
> @@ -498,6 +498,7 @@ static int svc_udp_get_dest_address(struct svc_rqst *rqstp,
>   	return 0;
>   }
>
> +extern int udp_sndbuf_nrpc, udp_rcvbuf_nrpc;
>   /*
>    * Receive a datagram from a UDP socket.
>    */
> @@ -521,18 +522,16 @@ static int svc_udp_recvfrom(struct svc_rqst *rqstp)
>   	size_t len;
>   	int err;
>
> -	if (test_and_clear_bit(XPT_CHNGBUF,&svsk->sk_xprt.xpt_flags))
> -	    /* udp sockets need large rcvbuf as all pending
> -	     * requests are still in that buffer.  sndbuf must
> -	     * also be large enough that there is enough space
> -	     * for one reply per thread.  We count all threads
> -	     * rather than threads in a particular pool, which
> -	     * provides an upper bound on the number of threads
> -	     * which will access the socket.
> -	     */
> -	    svc_sock_setbufsize(svsk->sk_sock,
> -				(serv->sv_nrthreads+3) * serv->sv_max_mesg,
> -				(serv->sv_nrthreads+3) * serv->sv_max_mesg);
> +	if (test_and_clear_bit(XPT_CHNGBUF,&svsk->sk_xprt.xpt_flags)) {
> +		/*
> +		 * UDP sockets need a large rcvbuf as all pending requests are
> +		 * still in that buffer.  sndbuf must also be large enough to
> +		 * fit a reply for each request the server could be processing.
> +		 */
> +		svc_sock_setbufsize(svsk->sk_sock,
> +				    udp_sndbuf_nrpc * serv->sv_max_mesg,
> +				    udp_rcvbuf_nrpc * serv->sv_max_mesg);
> +	}
>
>   	clear_bit(XPT_DATA,&svsk->sk_xprt.xpt_flags);
>   	skb = NULL;
> @@ -697,14 +696,14 @@ static void svc_udp_init(struct svc_sock *svsk, struct svc_serv *serv)
>   	clear_bit(XPT_CACHE_AUTH,&svsk->sk_xprt.xpt_flags);
>   	svsk->sk_sk->sk_data_ready = svc_udp_data_ready;
>   	svsk->sk_sk->sk_write_space = svc_write_space;
> -
> -	/* initialise setting must have enough space to
> -	 * receive and respond to one request.
> -	 * svc_udp_recvfrom will re-adjust if necessary
> +	
> +	/*
> +	 * Initial setting must have enough space to receive and respond to one
> +	 * request.  svc_udp_recvfrom will readjust if necessary.
>   	 */
>   	svc_sock_setbufsize(svsk->sk_sock,
> -			    3 * svsk->sk_xprt.xpt_server->sv_max_mesg,
> -			    3 * svsk->sk_xprt.xpt_server->sv_max_mesg);
> +			    6 * svsk->sk_xprt.xpt_server->sv_max_mesg,
> +			    6 * svsk->sk_xprt.xpt_server->sv_max_mesg);
>
>   	/* data might have come in before data_ready set up */
>   	set_bit(XPT_DATA,&svsk->sk_xprt.xpt_flags);
> @@ -874,6 +873,7 @@ failed:
>   	return NULL;
>   }
>
> +extern int tcp_sndbuf_nrpc, tcp_rcvbuf_nrpc;
>   /*
>    * Receive data.
>    * If we haven't gotten the record length yet, get the next four bytes.
> @@ -885,22 +885,20 @@ static int svc_tcp_recv_record(struct svc_sock *svsk, struct svc_rqst *rqstp)
>   	struct svc_serv	*serv = svsk->sk_xprt.xpt_server;
>   	int len;
>
> -	if (test_and_clear_bit(XPT_CHNGBUF,&svsk->sk_xprt.xpt_flags))
> -		/* sndbuf needs to have room for one request
> -		 * per thread, otherwise we can stall even when the
> -		 * network isn't a bottleneck.
> -		 *
> -		 * We count all threads rather than threads in a
> -		 * particular pool, which provides an upper bound
> -		 * on the number of threads which will access the socket.
> -		 *
> -		 * rcvbuf just needs to be able to hold a few requests.
> -		 * Normally they will be removed from the queue
> -		 * as soon a a complete request arrives.
> +	if (test_and_clear_bit(XPT_CHNGBUF,&svsk->sk_xprt.xpt_flags)) {
> +		/*
> +		 * sndbuf needs to have enough room for every request the
> +		 * server could be processing, otherwise we can block even when
> +		 * the network isn't a bottleneck.
> +		 *	
> +		 * Normally they will be removed from the queue as soon as a
> +		 * complete request arrives.
>   		 */
>   		svc_sock_setbufsize(svsk->sk_sock,
> -				    (serv->sv_nrthreads+3) * serv->sv_max_mesg,
> -				    3 * serv->sv_max_mesg);
> +				    tcp_sndbuf_nrpc * serv->sv_max_mesg,
> +				    tcp_rcvbuf_nrpc * serv->sv_max_mesg);
> +	}
> +
>
>   	clear_bit(XPT_DATA,&svsk->sk_xprt.xpt_flags);
>
> @@ -1250,13 +1248,14 @@ static void svc_tcp_init(struct svc_sock *svsk, struct svc_serv *serv)
>
>   		tcp_sk(sk)->nonagle |= TCP_NAGLE_OFF;
>
> -		/* initialise setting must have enough space to
> -		 * receive and respond to one request.
> -		 * svc_tcp_recvfrom will re-adjust if necessary
> +		/*
> +		 * Initial setting must have enough space to receive and
> +		 * respond to one request.  svc_tcp_recvfrom will readjust if
> +		 * necessary.
>   		 */
>   		svc_sock_setbufsize(svsk->sk_sock,
> -				    3 * svsk->sk_xprt.xpt_server->sv_max_mesg,
> -				    3 * svsk->sk_xprt.xpt_server->sv_max_mesg);
> +				    6 * svsk->sk_xprt.xpt_server->sv_max_mesg,
> +				    6 * svsk->sk_xprt.xpt_server->sv_max_mesg);
>
>   		set_bit(XPT_CHNGBUF,&svsk->sk_xprt.xpt_flags);
>   		set_bit(XPT_DATA,&svsk->sk_xprt.xpt_flags);
>
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-- 
Chuck Lever