linux-kernel - Re: [PATCH v3 3/7] sched: throttle cfs_rq entities which exceed their local quota

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Date:	Wed, 13 Oct 2010 15:34:21 +0900
From:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
To:	bharata@...ux.vnet.ibm.com
Cc:	linux-kernel@...r.kernel.org,
	Dhaval Giani <dhaval.giani@...il.com>,
	Balbir Singh <balbir@...ux.vnet.ibm.com>,
	Vaidyanathan Srinivasan <svaidy@...ux.vnet.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>,
	Paul Menage <menage@...gle.com>,
	Mike Waychison <mikew@...gle.com>,
	Paul Turner <pjt@...gle.com>, Nikhil Rao <ncrao@...gle.com>
Subject: Re: [PATCH v3 3/7] sched: throttle cfs_rq entities which exceed
 their local quota

On Tue, 12 Oct 2010 13:22:02 +0530
Bharata B Rao <bharata@...ux.vnet.ibm.com> wrote:

> sched: throttle cfs_rq entities which exceed their local quota
> 
> From: Paul Turner <pjt@...gle.com>
> 
> In account_cfs_rq_quota() (via update_curr()) we track consumption versus a
> cfs_rq's local quota and whether there is global quota available to continue
> enabling it in the event we run out.
> 
> This patch adds the required support for the latter case, throttling entities
> until quota is available to run.  Throttling dequeues the entity in question
> and sends a reschedule to the owning cpu so that it can be evicted.
> 
> The following restrictions apply to a throttled cfs_rq:
> - It is dequeued from sched_entity hierarchy and restricted from being
>   re-enqueued.  This means that new/waking children of this entity will be
>   queued up to it, but not past it.
> - It does not contribute to weight calculations in tg_shares_up
> - In the case that the cfs_rq of the cpu we are trying to pull from is throttled
>   it is  is ignored by the loadbalancer in __load_balance_fair() and
>   move_one_task_fair().
> 
> Signed-off-by: Paul Turner <pjt@...gle.com>
> Signed-off-by: Nikhil Rao <ncrao@...gle.com>
> Signed-off-by: Bharata B Rao <bharata@...ux.vnet.ibm.com>
> ---
>  kernel/sched.c      |   12 ++++++++
>  kernel/sched_fair.c |   70 ++++++++++++++++++++++++++++++++++++++++++++++++----
>  2 files changed, 76 insertions(+), 6 deletions(-)
> 
> --- a/kernel/sched.c
> +++ b/kernel/sched.c
> @@ -387,6 +387,7 @@ struct cfs_rq {
>  #endif
>  #ifdef CONFIG_CFS_BANDWIDTH
>  	u64 quota_assigned, quota_used;
> +	int throttled;
>  #endif
>  #endif
>  };
> @@ -1668,6 +1669,8 @@ static void update_group_shares_cpu(stru
>  	}
>  }
>  
> +static inline int cfs_rq_throttled(struct cfs_rq *cfs_rq);
> +

I just curious that static-inline forward declaration is inlined ?

>  /*
>   * Re-compute the task group their per cpu shares over the given domain.
>   * This needs to be done in a bottom-up fashion because the rq weight of a
> @@ -1688,7 +1691,14 @@ static int tg_shares_up(struct task_grou
>  	usd_rq_weight = per_cpu_ptr(update_shares_data, smp_processor_id());
>  
>  	for_each_cpu(i, sched_domain_span(sd)) {
> -		weight = tg->cfs_rq[i]->load.weight;
> +		/*
> +		 * bandwidth throttled entities cannot contribute to load
> +		 * balance
> +		 */
> +		if (!cfs_rq_throttled(tg->cfs_rq[i]))
> +			weight = tg->cfs_rq[i]->load.weight;
> +		else
> +			weight = 0;

cpu.share and bandwidth control can't be used simultaneously or...
is this fair ? I'm not familiar with scheduler but this allows boost this tg.
Could you add a brief documentaion of a spec/feature. in the next post ?

Thanks,
-Kame

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