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

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Message-ID: <AANLkTinSDt9U5py_PMVuNSgmqR0_PtCBxaCksuq8QR3F@mail.gmail.com>
Date:	Tue, 12 Oct 2010 23:44:29 -0700
From:	Paul Turner <pjt@...gle.com>
To:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
Cc:	bharata@...ux.vnet.ibm.com, 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>,
	Nikhil Rao <ncrao@...gle.com>
Subject: Re: [PATCH v3 3/7] sched: throttle cfs_rq entities which exceed their
 local quota

On Tue, Oct 12, 2010 at 11:34 PM, KAMEZAWA Hiroyuki
<kamezawa.hiroyu@...fujitsu.com> wrote:
> 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 ?
>

Hm.   This function is tiny, I should just move it up, thanks.

>>  /*
>>   * 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 ?
>

Bandwidth control is orthogonal to shares, shares continue controls
distribution of bandwidth when within quota.  Bandwidth control only
has 'perceivable' effect when you exceed your reservation within a
quota period.

What the above is doing is removing any throttled entities from the
load-balancer's weight calculations (based on contribution from
throttled entities) since these entities are already dequeued and
cannot be balanced.

Or have I misunderstood your question?

> Thanks,
> -Kame
>
>
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