Bug 235940 - [JAVA_BLOCKER] timekeeping starvation (sched_football hangs on RHEL5 RT)
[JAVA_BLOCKER] timekeeping starvation (sched_football hangs on RHEL5 RT)
Status: CLOSED CURRENTRELEASE
Product: Red Hat Enterprise MRG
Classification: Red Hat
Component: realtime-kernel (Show other bugs)
1.0
x86_64 Linux
medium Severity medium
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Assigned To: Clark Williams
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Depends On:
Blocks:
  Show dependency treegraph
 
Reported: 2007-04-10 17:45 EDT by IBM Bug Proxy
Modified: 2008-02-27 14:58 EST (History)
0 users

See Also:
Fixed In Version: 2.6.21-2.el5rt
Doc Type: Bug Fix
Doc Text:
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Clone Of:
Environment:
Last Closed: 2007-05-14 22:19:47 EDT
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Regression: ---
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CRM:
Verified Versions:
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oVirt Team: ---
RHEL 7.3 requirements from Atomic Host:
Cloudforms Team: ---


Attachments (Terms of Use)
tested cycles-accumulated patch sent to Ingo (7.24 KB, patch)
2007-04-10 17:45 EDT, IBM Bug Proxy
no flags Details | Diff
sysctrl-fix.patch (537 bytes, text/plain)
2007-04-24 21:40 EDT, IBM Bug Proxy
no flags Details


External Trackers
Tracker ID Priority Status Summary Last Updated
IBM Linux Technology Center 33424 None None None Never

  None (edit)
Description IBM Bug Proxy 2007-04-10 17:45:36 EDT
LTC Owner is: johnstul@us.ibm.com
LTC Originator is:  ankita@in.ibm.com


Problem description:
System hangs when running sched_football on RHEL5 RT.


Ok, I reproduced and it does look like the box is hung and its not just the
network. I need to dig and make sure its not the
oldtimekeeping-is-being-preempted issue of way back when.

Yep. update_wall_time() is currently called from a soft-irq, which can be
preempted. I'll need to re-implement the accumulate cycles code I did back for
2.6.16-rt

Ingo has picked up the patch upstream. Now we just need to get it pushed back
into 2.6.20-rt8
Comment 1 IBM Bug Proxy 2007-04-10 17:45:36 EDT
Created attachment 152183 [details]
tested cycles-accumulated patch sent to Ingo
Comment 2 IBM Bug Proxy 2007-04-10 19:35:47 EDT
----- Additional Comments From jstultz@us.ibm.com (prefers email at johnstul@us.ibm.com)  2007-04-10 19:32 EDT -------
Any objections to the patch from RedHat's side? 
Comment 3 Tim Burke 2007-04-13 15:10:43 EDT
Assigning to Clark to consider backporting Ingo's patch from 21 to 20.
Comment 4 john stultz 2007-04-23 16:13:40 EDT
Just a small update, Keith Mannthey has seemingly triggered this issue w/
2.6.21-rt (which includes my fix). So we're digging to figure out if additional
changes may be needed.

Comment 5 IBM Bug Proxy 2007-04-24 18:05:33 EDT
----- Additional Comments From jstultz@us.ibm.com (prefers email at johnstul@us.ibm.com)  2007-04-24 18:01 EDT -------
I'm confirmed an issue still exists with regards to timekeeping starvation in
2.6.21-rc6-rt0. I'm still working to narrow it down. 
Comment 6 IBM Bug Proxy 2007-04-24 21:26:12 EDT
----- Additional Comments From jstultz@us.ibm.com (prefers email at johnstul@us.ibm.com)  2007-04-24 21:22 EDT -------
Ok! I found it! Ingo has added a vsyscall hack (.sysctl_enabled = 2) on x86_64,
where the vsyscall just quickly returns the last calculated value of xtime
instead of reading the clocksource hardware (to improve speed).

This means gettimeofday has tick resolution, and further it loses robustness
under heavy -RT load (allows for starvation, as xtime won't be incremented until
the timer_softirq  runs).

I'm testing a patch to set the .sysctl_enabled back to 1 as the safe default. 
Comment 7 IBM Bug Proxy 2007-04-24 21:40:45 EDT
Created attachment 153395 [details]
sysctrl-fix.patch
Comment 8 IBM Bug Proxy 2007-04-24 21:41:01 EDT
----- Additional Comments From jstultz@us.ibm.com (prefers email at johnstul@us.ibm.com)  2007-04-24 21:36 EDT -------
 
don't enable the vsyscall_gtod returns walltime hack by default

Simply sets the vsyscall .sysctrl_enable to 1 instead of 2 to avoid the
vsyscall returns xtime hack that is prone to starvation. 
Comment 9 IBM Bug Proxy 2007-04-24 21:45:41 EDT
----- Additional Comments From jstultz@us.ibm.com (prefers email at johnstul@us.ibm.com)  2007-04-24 21:42 EDT -------
Patch sent to Ingo. 
Comment 10 IBM Bug Proxy 2007-05-02 20:05:51 EDT
----- Additional Comments From jstultz@us.ibm.com (prefers email at johnstul@us.ibm.com)  2007-05-02 20:02 EDT -------
I've confirmed Ingo included the patch in 2.6.21-rt1.
This can be closed once RH rebases on 2.6.21. 
Comment 11 IBM Bug Proxy 2007-05-10 18:25:46 EDT
----- Additional Comments From jstultz@us.ibm.com (prefers email at johnstul@us.ibm.com)  2007-05-10 18:23 EDT -------
Verified fixed in 2.6.21-2.el5rt kernel from Clark's repo. 

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