bin/112882: systat -tcp does not show tcp rexmit on sack enabled sockets (patch included)

[Phil Rosenthal]

>Number:         112882
>Category:       bin
>Synopsis:       systat -tcp does not show tcp rexmit on sack enabled sockets (patch included)
>Confidential:   no
>Severity:       non-critical
>Priority:       low
>Responsible:    freebsd-bugs
>State:          open
>Quarter:        
>Keywords:       
>Date-Required:
>Class:          update
>Submitter-Id:   current-users
>Arrival-Date:   Wed May 23 03:20:01 GMT 2007
>Closed-Date:
>Last-Modified:
>Originator:     Phil Rosenthal
>Release:        FreeBSD 6.2-STABLE amd64
>Organization:
ISPrime LLC
>Environment:
FreeBSD bmw2.isprime.com 6.2-STABLE FreeBSD 6.2-STABLE #0: Tue May 22 22:20:23 EDT 2007 root at bmw2.isprime.com:/usr/obj/usr/src/sys/BMW2 amd64
>Description:
FreeBSD's "systat" tool has a mode to display statistics for all tcp
sessions on the system. This mode is called by running "systat -tcp".

When a packet is retransmitted due to duplicate ack packets, or a timeout
waiting for an ack, tcps_sndrexmitpack is incremented.

When a packet is retransmitted due to a selective acknowledgement (sack),
tcps_sack_rexmits is incremented instead.

systat -tcp only shows tcps_sndrexmitpack, and given that most clients today
support sack, the user is falsely informed that there is a much lower amount
of packet loss/retransmits.

Additionally, the 9 digit values are easily overflowed on a server serving
hundreds of megabits of traffic which is becoming more commonplace given
the performance and wide availability of gig-e chipsets.

The patch referenced below fixes both of these issues.

>How-To-Repeat:
1)      Enable sack on both a client and a server, and set up a tcp socket.
2)      Cause packet loss (you can use dummynet for this)
3)      Watch systat -tcp

>Fix:
cd /usr/src/usr.bin/systat
fetch http://bmw2.isprime.com/systat-sack-rexmit.diff
patch < systat-sack-rexmit.diff
make
make install

This patch is built against FreeBSD 6.2-STABLE.  Earlier builds will fail with
this patch.

>Release-Note:
>Audit-Trail:
>Unformatted: