Some RPC transports have more overhead in their reply handlers
than others. For example, for RPC-over-RDMA:
- RPC completion has to wait for memory invalidation, which is
not a part of the server/network round trip
- Recently a context switch was introduced into the reply handler,
which further artificially inflates the measure of RPC RTT
To capture just server and network latencies more precisely: when
receiving a reply, compute the RTT as soon as the XID is recognized
rather than at RPC completion time.
Signed-off-by: Chuck Lever <chuck.lever@xxxxxxxxxx>
---
net/sunrpc/xprt.c | 5 +++--
1 file changed, 3 insertions(+), 2 deletions(-)
diff --git a/net/sunrpc/xprt.c b/net/sunrpc/xprt.c
index 13fbb48..cb7784c 100644
--- a/net/sunrpc/xprt.c
+++ b/net/sunrpc/xprt.c
@@ -826,6 +826,7 @@ static void xprt_connect_status(struct rpc_task *task)
* @xprt: transport on which the original request was transmitted
* @xid: RPC XID of incoming reply
*
+ * Caller holds xprt->recv_lock.
*/
struct rpc_rqst *xprt_lookup_rqst(struct rpc_xprt *xprt, __be32 xid)
{
@@ -834,6 +835,7 @@ struct rpc_rqst *xprt_lookup_rqst(struct rpc_xprt *xprt, __be32 xid)
list_for_each_entry(entry, &xprt->recv, rq_list)
if (entry->rq_xid == xid) {
trace_xprt_lookup_rqst(xprt, xid, 0);
+ entry->rq_rtt = ktime_sub(ktime_get(), entry->rq_xtime);
return entry;
}
@@ -915,7 +917,7 @@ void xprt_update_rtt(struct rpc_task *task)
* @task: RPC request that recently completed
* @copied: actual number of bytes received from the transport
*
- * Caller holds transport lock.
+ * Caller holds xprt->recv_lock.
*/
void xprt_complete_rqst(struct rpc_task *task, int copied)
{
@@ -927,7 +929,6 @@ void xprt_complete_rqst(struct rpc_task *task, int copied)
trace_xprt_complete_rqst(xprt, req->rq_xid, copied);
xprt->stat.recvs++;
- req->rq_rtt = ktime_sub(ktime_get(), req->rq_xtime);
list_del_init(&req->rq_list);
req->rq_private_buf.len = copied;
--
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