linux-kernel - Re: [CFS Bandwidth Control v4 6/7] sched: hierarchical task accounting for SCHED

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Date:	Tue, 22 Feb 2011 18:20:05 -0800
From:	Paul Turner <pjt@...gle.com>
To:	Hidetoshi Seto <seto.hidetoshi@...fujitsu.com>
Cc:	linux-kernel@...r.kernel.org,
	Bharata B Rao <bharata@...ux.vnet.ibm.com>,
	Dhaval Giani <dhaval@...ux.vnet.ibm.com>,
	Balbir Singh <balbir@...ux.vnet.ibm.com>,
	Vaidyanathan Srinivasan <svaidy@...ux.vnet.ibm.com>,
	Gautham R Shenoy <ego@...ibm.com>,
	Srivatsa Vaddagiri <vatsa@...ibm.com>,
	Kamalesh Babulal <kamalesh@...ux.vnet.ibm.com>,
	Ingo Molnar <mingo@...e.hu>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Pavel Emelyanov <xemul@...nvz.org>,
	Herbert Poetzl <herbert@...hfloor.at>,
	Avi Kivity <avi@...hat.com>,
	Chris Friesen <cfriesen@...tel.com>
Subject: Re: [CFS Bandwidth Control v4 6/7] sched: hierarchical task
 accounting for SCHED_OTHER

On Tue, Feb 22, 2011 at 6:02 PM, Hidetoshi Seto
<seto.hidetoshi@...fujitsu.com> wrote:
> (2011/02/16 12:18), Paul Turner wrote:
>> @@ -1428,6 +1464,7 @@ enqueue_task_fair(struct rq *rq, struct
>>               update_cfs_shares(cfs_rq);
>>       }
>>
>> +     account_hier_tasks(&p->se, 1);
>>       hrtick_update(rq);
>>  }
>>
>> @@ -1461,6 +1498,7 @@ static void dequeue_task_fair(struct rq
>>               update_cfs_shares(cfs_rq);
>>       }
>>
>> +     account_hier_tasks(&p->se, -1);
>>       hrtick_update(rq);
>>  }
>>
>
> Why hrtick_update() is need to be delayed after modifying nr_running?
> You should not impact current hrtick logic without once mentioning.

There shouldn't be any impact -- hrtick_update only cares about
cfs_rq->nr_running which is independent of rq->nr_running (maintained
by hierarchal accounting)

>
>> Index: tip/kernel/sched_rt.c
>> ===================================================================
>> --- tip.orig/kernel/sched_rt.c
>> +++ tip/kernel/sched_rt.c
>> @@ -906,6 +906,8 @@ enqueue_task_rt(struct rq *rq, struct ta
>>
>>       if (!task_current(rq, p) && p->rt.nr_cpus_allowed > 1)
>>               enqueue_pushable_task(rq, p);
>> +
>> +     inc_nr_running(rq);
>>  }
>>
>>  static void dequeue_task_rt(struct rq *rq, struct task_struct *p, int flags)
>> @@ -916,6 +918,8 @@ static void dequeue_task_rt(struct rq *r
>>       dequeue_rt_entity(rt_se);
>>
>>       dequeue_pushable_task(rq, p);
>> +
>> +     dec_nr_running(rq);
>>  }
>>
>>  /*
>
> I think similar change for sched_stoptask.c is required.

Aha!

Yes, I missed this addition when re-basing.

It is needed since when something is placed into the stop-class via
set_sched it goes through an activate/deactivate.

Will add, thanks!

>
> In fact I could not boot tip/master with this v4 patchset.
> It reports rcu stall warns without applying following tweak:
>
> --- a/kernel/sched_stoptask.c
> +++ b/kernel/sched_stoptask.c
> @@ -35,11 +35,13 @@ static struct task_struct *pick_next_task_stop(struct rq *rq
>  static void
>  enqueue_task_stop(struct rq *rq, struct task_struct *p, int flags)
>  {
> +       inc_nr_running(rq);
>  }
>
>  static void
>  dequeue_task_stop(struct rq *rq, struct task_struct *p, int flags)
>  {
> +       dec_nr_running(rq);
>  }
>
>
> Thanks,
> H.Seto
>
>
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