Date: Sun, 26 Oct 2008 19:15:57 GMT From: Mihail Balikov <mgb.fbsd@gmail.com> To: freebsd-gnats-submit@FreeBSD.org Subject: kern/128401: dummynet does not shape traffic with fast io enabled Message-ID: <200810261915.m9QJFvBm089264@www.freebsd.org> Resent-Message-ID: <200810261920.m9QJK2VQ047331@freefall.freebsd.org>
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>Number: 128401
>Category: kern
>Synopsis: dummynet does not shape traffic with fast io enabled
>Confidential: no
>Severity: serious
>Priority: medium
>Responsible: freebsd-bugs
>State: open
>Quarter:
>Keywords:
>Date-Required:
>Class: sw-bug
>Submitter-Id: current-users
>Arrival-Date: Sun Oct 26 19:20:01 UTC 2008
>Closed-Date:
>Last-Modified:
>Originator: Mihail Balikov
>Release: FreeBSD6, FreeBSD7
>Organization:
Megalan Network
>Environment:
FreeBSD freebsd7.megalan.bg 7.1-PRERELEASE FreeBSD 7.1-PRERELEASE #0: Thu Oct 23 10:51:58 EEST 2008 root@freebsd7.megalan.bg:/usr/src/sys/i386/compile/mBSD7 i386
>Description:
On freebsd7 with hz=2000 dummynet stops shaping traffic after 25 days uptime.
I have tracked down the problem in dummynet io fast code at ip_dummynet.c:1353
if (q->q_time < curr_time)
q->numbytes = io_fast ? fs->pipe->bandwidth : 0;
This comparision is incorrect. q->q_time is u_int32_t and curr_time is u_int64_t.
After (1<<32) / hz seconds (~24days when hz=2000) q->q_time is always smaller than curr_time.
This is long standing bug, which also affects on RED.
>How-To-Repeat:
>Fix:
1) workaround: disable io fast
sysctl net.inet.ip.dummynet.io_fast=0
2) change q_time type to dn_key in ip_dummynet.h. ipfw userland program needs to be recompiled.
3) compare q_time with (curr_time & 0xffffffff). RED code (red_drops()) also should be revised.
>Release-Note:
>Audit-Trail:
>Unformatted:
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