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Date: Mon, 20 Nov 2006 16:14:47 -0600
From: Clark Williams <williams@redhat.com>
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To: Ingo Molnar <mingo@elte.hu>, Thomas Gleixner <tglx@linutronix.de>,
       john stultz <johnstul@us.ibm.com>
CC: LKML <linux-kernel@vger.kernel.org>
Subject: Time warp on 2.6.19-rc6-rt4
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Ingo/Thomas/John/et al,

I've seen sporadic time warp messages while running my pi_stress program
(http://people.redhat.com/williams/tests/pi_tests-1.7.tar.gz). The
frequency of time warp occurrences has been gong down over time, but I
just got one on a dual Opteron running 2.6.19-rc6-rt4:

- --------------
$ sudo ./pi_stress --signal
Starting PI Stress test
    Test threads using scheduler policy: SCHED_FIFO
      Admin priority:    99
      Reporter priority: 98
    10 groups of 3 threads will be created
      High priority:     97
      Med priority:      96
      Low priority:      95
    Admin threads running on processor: 0
    Test threads running on processor:  1
Press Ctrl-C to stop test
Current Inversions: 1032940
Stoppping test
Total inversion performed: 6836686
- --------------

The Current Inversions line is dynamically updated, but after I noticed
it had stopped updating, I looked a the console and found:

- --------------
BUG: time warp detected!
prev > now, 10277e5c84132156 > 10277e5b6c9e0baf:
= 4688516519 delta, on CPU#0

Call Trace:
 [<ffffffff8026e647>] dump_trace+0xaa/0x3f2
 [<ffffffff8026e9c9>] show_trace+0x3a/0x58
 [<ffffffff8026ec03>] dump_stack+0x15/0x17
 [<ffffffff8025cd91>] getnstimeofday+0x142/0x150
 [<ffffffff802a2aff>] sys_clock_gettime+0x4d/0x98
 [<ffffffff802601cf>] system_call+0xef/0x15c
DWARF2 unwinder stuck at system_call+0xef/0x15c

Leftover inexact backtrace:


skipping trace printing on CPU#0 != -1
hdb: lost interrupt
hdb: lost interrupt
- --------------

The system was still running, but in my test the timer wasn't updating.
This was actually one of Ingo's prepackaged kernel-rt rpms, so I don't
have much debug on.

Anything you want me to try?

Clark
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