i386/148429: net.inet.ip.dummynet.io_fast broken or documentation incomplete.

[Paul-Andrew Joseph Miseiko]

>Number:         148429
>Category:       i386
>Synopsis:       net.inet.ip.dummynet.io_fast broken or documentation incomplete.
>Confidential:   no
>Severity:       non-critical
>Priority:       low
>Responsible:    freebsd-i386
>State:          open
>Quarter:        
>Keywords:       
>Date-Required:
>Class:          sw-bug
>Submitter-Id:   current-users
>Arrival-Date:   Wed Jul 07 15:30:03 UTC 2010
>Closed-Date:
>Last-Modified:
>Originator:     Paul-Andrew Joseph Miseiko
>Release:        8.0-STABLE
>Organization:
>Environment:
FreeBSD teardrop.ca 8.0-STABLE FreeBSD 8.0-STABLE #0: Tue Apr 27 10:28:56 EDT 2010     esoteric at teardrop.ca:/usr/obj/usr/src/sys/TEARDROP  i386
>Description:
The IPFW manual page TRAFFIC SHAPER (DUMMYNET) CONFIGURATION section stated “The ``fast'' mode allows certain packets to bypass the dummynet scheduler (if packet flow does not exceed pipe's bandwidth).”

The statement is false when a queue is used and multiple flows are present.  The combined bandwidth of each flow can exceed the pipe bandwidth.

The statement is true when a queue is used and a single flow is present.
>How-To-Repeat:
sysctl net.inet.ip.dummynet.io_fast=1

ipfw pipe 1 config bw 4096kbit/s
ipfw queue 1 config pipe 1 mask dst-ip 0xffffffff

ipfw add queue 1 pass all from any to any

--- transmit data with multiple flows (connections) ---

The destination IP address used to reproduce this issue was the same.  Different destination IP addresses have not been used to reproduce this issue at this time but might exhibit the same behavior.
>Fix:
sysctl net.inet.ip.dummynet.io_fast=0

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