linux-kernel - [PATCH 03/10] staging/lustre/ptlrpc: false alarm in AT network latency measuring

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Date:	Wed, 25 Mar 2015 21:53:19 -0400
From:	green@...uxhacker.ru
To:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	devel@...verdev.osuosl.org,
	Andreas Dilger <andreas.dilger@...el.com>
Cc:	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Liang Zhen <liang.zhen@...el.com>,
	Oleg Drokin <oleg.drokin@...el.com>
Subject: [PATCH 03/10] staging/lustre/ptlrpc: false alarm in AT network latency measuring

From: Liang Zhen <liang.zhen@...el.com>

If early reply of client RPC is lost and client RPC is expired and
resent, server will drop the resent RPC because it's already in
processing, server may also send reply or early reply to client,
which can still match reply buffer of the original request.
In this case, client is measuring time from resent time, but server
is reporting service time of original RPC, which is longer than
the time measured by client.

Signed-off-by: Liang Zhen <liang.zhen@...el.com>
Reviewed-on: http://review.whamcloud.com/12855
Intel-bug-id: https://jira.hpdd.intel.com/browse/LU-5545
Reviewed-by: Li Wei <wei.g.li@...el.com>
Reviewed-by: Johann Lombardi <johann.lombardi@...el.com>
Signed-off-by: Oleg Drokin <oleg.drokin@...el.com>
---
 drivers/staging/lustre/lustre/ptlrpc/client.c | 25 +++++++++++++++++++------
 1 file changed, 19 insertions(+), 6 deletions(-)

diff --git a/drivers/staging/lustre/lustre/ptlrpc/client.c b/drivers/staging/lustre/lustre/ptlrpc/client.c
index 0fe6a64..0357f1d 100644
--- a/drivers/staging/lustre/lustre/ptlrpc/client.c
+++ b/drivers/staging/lustre/lustre/ptlrpc/client.c
@@ -285,14 +285,27 @@ static void ptlrpc_at_adj_net_latency(struct ptlrpc_request *req,
 	time_t now = get_seconds();
 
 	LASSERT(req->rq_import);
-	at = &req->rq_import->imp_at;
+
+	if (service_time > now - req->rq_sent + 3) {
+		/* bz16408, however, this can also happen if early reply
+		 * is lost and client RPC is expired and resent, early reply
+		 * or reply of original RPC can still be fit in reply buffer
+		 * of resent RPC, now client is measuring time from the
+		 * resent time, but server sent back service time of original
+		 * RPC.
+		 */
+		CDEBUG((lustre_msg_get_flags(req->rq_reqmsg) & MSG_RESENT) ?
+		       D_ADAPTTO : D_WARNING,
+		       "Reported service time %u > total measured time "
+		       CFS_DURATION_T"\n", service_time,
+		       cfs_time_sub(now, req->rq_sent));
+		return;
+	}
 
 	/* Network latency is total time less server processing time */
-	nl = max_t(int, now - req->rq_sent - service_time, 0) + 1/*st rounding*/;
-	if (service_time > now - req->rq_sent + 3 /* bz16408 */)
-		CWARN("Reported service time %u > total measured time "
-		      CFS_DURATION_T"\n", service_time,
-		      cfs_time_sub(now, req->rq_sent));
+	nl = max_t(int, now - req->rq_sent -
+			service_time, 0) + 1; /* st rounding */
+	at = &req->rq_import->imp_at;
 
 	oldnl = at_measured(&at->iat_net_latency, nl);
 	if (oldnl != 0)
-- 
2.1.0

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