linux-kernel - Re: [PATCH bisected regression] sched: rebuild sched domains at suspend/resume

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Message-ID: <4F578176.9060808@openvz.org>
Date:	Wed, 07 Mar 2012 19:40:38 +0400
From:	Konstantin Khlebnikov <khlebnikov@...nvz.org>
To:	"Srivatsa S. Bhat" <srivatsa.bhat@...ux.vnet.ibm.com>
CC:	Ingo Molnar <mingo@...e.hu>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	"prashanth@...ux.vnet.ibm.com" <prashanth@...ux.vnet.ibm.com>,
	"Rafael J. Wysocki" <rjw@...k.pl>,
	Linux PM mailing list <linux-pm@...r.kernel.org>,
	Srivatsa Vaddagiri <vatsa@...ux.vnet.ibm.com>,
	"paulmck@...ux.vnet.ibm.com >> \"Paul E. McKenney\"" 
	<paulmck@...ux.vnet.ibm.com>
Subject: Re: [PATCH bisected regression] sched: rebuild sched domains at suspend/resume

Srivatsa S. Bhat wrote:
> On 03/07/2012 02:15 AM, Konstantin Khlebnikov wrote:
>
>> This is fix for suspend/resume regression introduced in commit 8f2f748b0656
>> ("CPU hotplug, cpusets, suspend: Don't touch cpusets during suspend/resume")
>> Without this patch suspend always hangs on my thinkpad x220 (2 x CPU * HT).
>>
>
>
> Hey, with commit 8f2f748b0656, suspend/resume works perfectly for me! I ran it
> multiple times just to make sure, and everything worked just great.
>
> Apart from that, I even tried suspend/resume after building the kernel with
> and without CONFIG_CPUSETS. Both cases worked perfectly.
>
> So, I am really surprised at what you stated above. Are you *really* sure you
> are facing suspend hangs *because* of the above commit?
>
> And AFAICS hardware doesn't matter for the code in question, but in any case,
> the laptop on which I tested it is:
> Thinkpad T420 (Intel core i5-2540M), 2 cores * HT (total 4 logical cpus).
>
> Also, the patch you posted here doesn't make much sense.. nor does it give a
> clue as to what might be wrong at your end (if anything is really wrong, that
> is). Do you have CONFIG_CPUSETS set or unset? Could you share your .config?

my kernel config in attachment. CONFIG_CPUSETS=n

>
> Coming to your patch, assuming you have CONFIG_CPUSETS enabled, then,
> calling rebuild_sched_domains() at that point is useless because the cpusets
> weren't changed at all. So generate_sched_domains() would generate the same
> sched domain partitions that is already there.. And hence
> partition_sched_domains() would essentially do nothing.. no sched domain is
> destroyed, and no new domains are created.
>
> However, if CONFIG_CPUSETS is unset, then, before commit 8f2f748b0656,
> partition_sched_domains(1, NULL, NULL) would have been invoked, thus rebuilding
> a single sched domain. And that is why I specifically also tested commit
> 8f2f748b0656 with CONFIG_CPUSETS unset - and that also worked fine (as I
> mentioned above).
>
> So could you please check again?
>
> By the way, you can use the pm-test framework (see Documentation/power/basic-
> pm-debugging.txt) to pin-point which stage is causing the hang.
> Specifically, the stage where CPU hotplug is done is 'processors'.
>
> So you should probably try out this level:
> # echo processors>  /sys/power/pm_test
> # echo mem>  /sys/power/state
>
> Replacing processors with core enables even deeper level suspend testing.

Your patch has obvious side-effect.
Bug reproducing is very stable, it disappears if revert your patch or apply mine.
Problem may be not in your patch, it may only trigger some longstanding bug.
I can test debug patches, but I'm not going to just dig around -- it's not my business.

>
>> cpuset_update_active_cpus() not only juggles with bits in cpusets,
>> it also calls sched-domains rebuilding after all.
>>
>> This patch restores sched-domain rebuilds, as it was before that commit.
>>
>> Signed-off-by: Konstantin Khlebnikov<khlebnikov@...nvz.org>
>> ---
>>   kernel/sched/core.c |    7 +++++++
>>   1 files changed, 7 insertions(+), 0 deletions(-)
>>
>> diff --git a/kernel/sched/core.c b/kernel/sched/core.c
>> index 9995eb0..0fb7406 100644
>> --- a/kernel/sched/core.c
>> +++ b/kernel/sched/core.c
>> @@ -6732,6 +6732,10 @@ static int cpuset_cpu_active(struct notifier_block *nfb, unsigned long action,
>>   	case CPU_DOWN_FAILED:
>>   		cpuset_update_active_cpus();
>>   		return NOTIFY_OK;
>> +	case CPU_ONLINE_FROZEN:
>> +	case CPU_DOWN_FAILED_FROZEN:
>> +		rebuild_sched_domains();
>> +		return NOTIFY_OK;
>>   	default:
>>   		return NOTIFY_DONE;
>>   	}
>> @@ -6744,6 +6748,9 @@ static int cpuset_cpu_inactive(struct notifier_block *nfb, unsigned long action,
>>   	case CPU_DOWN_PREPARE:
>>   		cpuset_update_active_cpus();
>>   		return NOTIFY_OK;
>> +	case CPU_DOWN_PREPARE_FROZEN:
>> +		rebuild_sched_domains();
>> +		return NOTIFY_OK;
>>   	default:
>>   		return NOTIFY_DONE;
>>   	}
>>
>
>
> Regards,
> Srivatsa S. Bhat
> IBM Linux Technology Center
>
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