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Commit 0b87a46b authored by Chuck Lever's avatar Chuck Lever Committed by Anna Schumaker
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SUNRPC: Make RTT measurement more precise (Receive) 



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: default avatarChuck Lever <chuck.lever@oracle.com>
Signed-off-by: default avatarAnna Schumaker <Anna.Schumaker@Netapp.com>
parent ecd465ee

net/sunrpc/xprt.c

+3 −2
Original line number Diff line number Diff line
@@ -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 @@ EXPORT_SYMBOL_GPL(xprt_update_rtt); 
 * @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;