Bug 445713 - tsc going back bug
tsc going back bug
Status: CLOSED DUPLICATE of bug 443435
Product: Red Hat Enterprise Linux 5
Classification: Red Hat
Component: kernel (Show other bugs)
5.1
i386 Linux
low Severity low
: rc
: ---
Assigned To: Red Hat Kernel Manager
Martin Jenner
: Reopened
Depends On:
Blocks:
  Show dependency treegraph
 
Reported: 2008-05-08 14:10 EDT by Alok Kataria
Modified: 2008-05-27 13:55 EDT (History)
3 users (show)

See Also:
Fixed In Version:
Doc Type: Bug Fix
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Clone Of:
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Last Closed: 2008-05-27 13:55:09 EDT
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oVirt Team: ---
RHEL 7.3 requirements from Atomic Host:
Cloudforms Team: ---


Attachments (Terms of Use)
fix for tsc going back problem. (4.24 KB, patch)
2008-05-08 14:10 EDT, Alok Kataria
no flags Details | Diff

  None (edit)
Description Alok Kataria 2008-05-08 14:10:57 EDT
Description of problem:

There were a few recent reports of tsc going back on LKML, as a result of which
there could be cases when time (gettimeofday) jumps in the future.
http://lkml.org/lkml/2007/8/23/96
http://lkml.org/lkml/2008/3/31/23

I did some kernel instrumentation on the recent RHEL5.1 kernel 
2.6.18-53.1.19.el5, and see that read_tsc does jump back once in a while on my
dual core box. As a result the value returned from read_tsc <
clocksource->cycle_last value, which results in large values of offset due to
the unsigned arithmetic involved (have a look at update_wall_time). Eventually
results in some bogus gettimeofday values.

There was a fix for this problem from Thomas Gleixner which was included in the
2.6.26-rc1 tree. 
http://git.kernel.org/?p=linux/kernel/git/torvalds/linux-2.6.git;a=commit;h=d8bb6f4c1670c8324e4135c61ef07486f7f17379

Attached is a backport of this fix. This is required on all RHEL kernels that
use clocksource. 

Version-Release number of selected component (if applicable):


How reproducible:


Steps to Reproduce:
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Additional info:
Comment 1 Alok Kataria 2008-05-08 14:10:57 EDT
Created attachment 304882 [details]
fix for tsc going back problem.
Comment 2 Prarit Bhargava 2008-05-12 08:53:22 EDT

*** This bug has been marked as a duplicate of 443435 ***
Comment 3 Alok Kataria 2008-05-12 19:21:30 EDT
(In reply to comment #2)
> 
> *** This bug has been marked as a duplicate of 443435 ***

I am not authorized to access that BUG, 
It says

"You are not authorized to access bug #443435.

Access to some bugs is restricted due to embargoed security issues or respect
for customer and partner information which must remain confidential."

Is there a way that I can look at that BUG ? Maybe you can add me to the CC list
for bug #443435 ?

Thanks,
Alok
Comment 4 Alok Kataria 2008-05-14 21:14:23 EDT
(In reply to comment #2)
> 
> *** This bug has been marked as a duplicate of 443435 ***

Prarit,

Let me know if there is anyway to access that bug #443435. 
Comment 5 Alok Kataria 2008-05-15 20:49:30 EDT
Still need access to bug #443435
Need to know if you guys already have the fix and if so which kernel release is
going to have that fix.

Thanks,
Alok

(In reply to comment #3)
> (In reply to comment #2)
> > 
> > *** This bug has been marked as a duplicate of 443435 ***
> 
> I am not authorized to access that BUG, 
> It says
> 
> "You are not authorized to access bug #443435.
> 
> Access to some bugs is restricted due to embargoed security issues or respect
> for customer and partner information which must remain confidential."
> 
> Is there a way that I can look at that BUG ? Maybe you can add me to the CC list
> for bug #443435 ?
> 
> Thanks,
> Alok

Comment 6 Prarit Bhargava 2008-05-27 13:55:09 EDT
Alok, the latest RHEL5 kernel has this patch.

P.

*** This bug has been marked as a duplicate of 443435 ***

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