sunrpc: Report per-RPC execution stats

Introduce a mechanism to report the server-side execution latency of
each RPC. The goal is to enable user space to filter the trace
record for latency outliers, build histograms, etc.
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
Signed-off-by: J. Bruce Fields <bfields@redhat.com>

include/linux/sunrpc/svc.h

@@ -283,6 +283,7 @@ struct svc_rqst {
 	int			rq_reserved;	/* space on socket outq
 						 * reserved for this request
 						 */
+	ktime_t			rq_stime;	/* start time */
 
 	struct cache_req	rq_chandle;	/* handle passed to caches for 
 						 * request delaying 

include/trace/events/sunrpc.h

@@ -705,6 +705,27 @@ TRACE_EVENT(svc_handle_xprt,
 		__entry->len, show_svc_xprt_flags(__entry->flags))
 );
 
+TRACE_EVENT(svc_stats_latency,
+	TP_PROTO(const struct svc_rqst *rqst),
+
+	TP_ARGS(rqst),
+
+	TP_STRUCT__entry(
+		__field(u32, xid)
+		__field(unsigned long, execute)
+		__string(addr, rqst->rq_xprt->xpt_remotebuf)
+	),
+
+	TP_fast_assign(
+		__entry->xid = be32_to_cpu(rqst->rq_xid);
+		__entry->execute = ktime_to_us(ktime_sub(ktime_get(),
+							 rqst->rq_stime));
+		__assign_str(addr, rqst->rq_xprt->xpt_remotebuf);
+	),
+
+	TP_printk("addr=%s xid=0x%08x execute-us=%lu",
+		__get_str(addr), __entry->xid, __entry->execute)
+);
 
 DECLARE_EVENT_CLASS(svc_deferred_event,
 	TP_PROTO(struct svc_deferred_req *dr),

net/sunrpc/svc_xprt.c

@@ -782,7 +782,7 @@ static int svc_handle_xprt(struct svc_rqst *rqstp, struct svc_xprt *xprt)
 			len = svc_deferred_recv(rqstp);
 		else
 			len = xprt->xpt_ops->xpo_recvfrom(rqstp);
-		dprintk("svc: got len=%d\n", len);
+		rqstp->rq_stime = ktime_get();
 		rqstp->rq_reserved = serv->sv_max_mesg;
 		atomic_add(rqstp->rq_reserved, &xprt->xpt_reserved);
 	}
@@ -888,6 +888,7 @@ int svc_send(struct svc_rqst *rqstp)
 
 	/* Grab mutex to serialize outgoing data. */
 	mutex_lock(&xprt->xpt_mutex);
+	trace_svc_stats_latency(rqstp);
 	if (test_bit(XPT_DEAD, &xprt->xpt_flags)
 			|| test_bit(XPT_CLOSE, &xprt->xpt_flags))
 		len = -ENOTCONN;