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Date: Mon, 06 Jun 2005 15:20:13 +0900 (JST)
Message-Id: <20050606.152013.55717574.Noritoshi@Demizu.ORG>
From: Noritoshi Demizu <demizu@dd.iij4u.or.jp>
To: Jiawei Ye <leafy7382@gmail.com>
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Cc: freebsd-current@freebsd.org
Subject: Re: Is this the sign of a problem?
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> The following message repeats quite often in /var/log/messages
>  kernel: tcp_sack_output: Computed sack_bytes_retransmitted (2636) not
> the same as cached value (5307)
>
> Is this a sign of problems?

Yes. Thanks for your report.

The patch below would fix the problem.  It will be committed soon.

Regards,
Noritoshi Demizu


Index: tcp_sack.c
===================================================================
RCS file: /home/cvsup/FreeBSD/ncvs/src/sys/netinet/tcp_sack.c,v
retrieving revision 1.21
diff -u -r1.21 tcp_sack.c
--- tcp_sack.c	4 Jun 2005 08:03:28 -0000	1.21
+++ tcp_sack.c	6 Jun 2005 03:21:26 -0000
@@ -508,8 +508,6 @@
 				cur->start = sblkp->end;
 				cur->rxmit = SEQ_MAX(cur->rxmit, cur->start);
 			}
-			/* Go to the previous hole. */
-			cur = TAILQ_PREV(cur, sackhole_head, scblink);
 		} else {
 			/* Data acks at least the end of hole */
 			if (SEQ_GEQ(sblkp->end, cur->end)) {
@@ -535,10 +533,17 @@
 							     cur->end);
 				}
 			}
-			/* Go to the previous sack block. */
-			sblkp--;
 		}
 		tp->sackhint.sack_bytes_rexmit += (cur->rxmit - cur->start);
+		/*
+		 * Testing sblkp->start against cur->start tells us whether
+		 * we're done with the sack block or the sack hole.
+		 * Accordingly, we advance one or the other.
+		 */
+		if (SEQ_LEQ(sblkp->start, cur->start))
+			cur = TAILQ_PREV(cur, sackhole_head, scblink);
+		else
+			sblkp--;
 	}
 	return (0);
 }