linux-kernel - Re: [GIT PULL rcu/next] rcu commits for 2.6.40

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Date:	Thu, 12 May 2011 18:28:45 -0700
From:	Yinghai Lu <yinghai@...nel.org>
To:	paulmck@...ux.vnet.ibm.com
CC:	Ingo Molnar <mingo@...e.hu>, linux-kernel@...r.kernel.org
Subject: Re: [GIT PULL rcu/next] rcu commits for 2.6.40

On 05/12/2011 02:36 PM, Yinghai Lu wrote:
> On 05/12/2011 02:20 AM, Paul E. McKenney wrote:
>> On Thu, May 12, 2011 at 12:42:50AM -0700, Yinghai Lu wrote:
>>> On 05/12/2011 12:27 AM, Yinghai Lu wrote:
>>>> On 05/11/2011 11:03 PM, Ingo Molnar wrote:
>>>>>
>>>>> * Yinghai Lu <yinghai@...nel.org> wrote:
>>>>>
>>>>>> e59fb3120becfb36b22ddb8bd27d065d3cdca499 is the first bad commit
>>>>>> commit e59fb3120becfb36b22ddb8bd27d065d3cdca499
>>>>>> Author: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>
>>>>>> Date:   Tue Sep 7 10:38:22 2010 -0700
>>>>>>
>>>>>>     rcu: Decrease memory-barrier usage based on semi-formal proof
>>>>>
>>>>> Find below an (untested!) attempt at reverting it for debugging purposes: could 
>>>>> you please try it, does your system now boot up fine?
>>>>>
>>>>> Thanks,
>>>>>
>>>>> 	Ingo
>>>>>
>>>>
>>>> yes, reverted manually that commit fix the problem.
>>>
>>> on system with 8 sockets westmere-ex
>>>
>>> it seems other commits after that commit contribute some delay too.
>>>
>>> [   32.240739] cpu_dev_init done
>>> [   73.587288] memory_dev_init done
>>
>> I am testing a revert of e59fb3120becfb36b22ddb8bd27d065d3cdca499 and
>> will chase down the delay.
>>
> 
> it seems still need to revert following one in addition  e59fb3120becfb36b22ddb8bd27d065d3cdca499.
> 
> [root@...14-2404-239-158 linux-2.6]# git bisect good
> a26ac2455ffcf3be5c6ef92bc6df7182700f2114 is the first bad commit
> commit a26ac2455ffcf3be5c6ef92bc6df7182700f2114
> Author: Paul E. McKenney <paul.mckenney@...aro.org>
> Date:   Wed Jan 12 14:10:23 2011 -0800
> 
>     rcu: move TREE_RCU from softirq to kthread
>     
>     If RCU priority boosting is to be meaningful, callback invocation must
>     be boosted in addition to preempted RCU readers.  Otherwise, in presence
>     of CPU real-time threads, the grace period ends, but the callbacks don't
>     get invoked.  If the callbacks don't get invoked, the associated memory
>     doesn't get freed, so the system is still subject to OOM.
>     
>     But it is not reasonable to priority-boost RCU_SOFTIRQ, so this commit
>     moves the callback invocations to a kthread, which can be boosted easily.
>     
>     Also add comments and properly synchronized all accesses to
>     rcu_cpu_kthread_task, as suggested by Lai Jiangshan.
>     
>     Signed-off-by: Paul E. McKenney <paul.mckenney@...aro.org>
>     Signed-off-by: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>
>     Reviewed-by: Josh Triplett <josh@...htriplett.org>
> 
> :040000 040000 e40306ac6405952c1d387325a98588442209abe8 efe9ea2f408c62daaccf49e6d1339dff3a74f049 M	Documentation
> :040000 040000 8f9e7a8fa3a728d4ae58e2efb8ada7cf08aed00e 9b44deba45ba905c5d9b3cc314812f0ba3f7e639 M	include
> :040000 040000 4b10b719a2d56ed4bc796a9f43775732bb5ff144 4db269277ccf607e1a6a7d7f4c2a7cf8d592d46a M	kernel
> :040000 040000 881f102e6831381beed016ed240d690f6a2ccd5e 57d2fc6f84e47394c116bc617a9a0ef9b8b6dbd4 M	tools

more info:
if only reverting: e59fb3120becfb36b22ddb8bd27d065d3cdca499

when compiled with gcc from opensuse 11.3
[   32.579585] cpu_dev_init done
[   81.203193] memory_dev_init done

but when compile that with gcc from fedora 14, then will less delay.
[   32.404140] cpu_dev_init done
[   37.602986] memory_dev_init done

gcc version on opensuse 11.3
gcc (SUSE Linux) 4.5.0 20100604 [gcc-4_5-branch revision 160292]

gcc version on fedora 14:
gcc (GCC) 4.5.1 20100924 (Red Hat 4.5.1-4)

Thanks

Yinghai
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