[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]
Date: Mon, 8 Aug 2011 09:16:00 -0700
From: Paul Turner <pjt@...gle.com>
To: Lin Ming <minggr@...il.com>
Cc: Peter Zijlstra <a.p.zijlstra@...llo.nl>,
linux-kernel@...r.kernel.org,
Bharata B Rao <bharata@...ux.vnet.ibm.com>,
Dhaval Giani <dhaval.giani@...il.com>,
Balbir Singh <bsingharora@...il.com>,
Vaidyanathan Srinivasan <svaidy@...ux.vnet.ibm.com>,
Srivatsa Vaddagiri <vatsa@...ibm.com>,
Kamalesh Babulal <kamalesh@...ux.vnet.ibm.com>,
Hidetoshi Seto <seto.hidetoshi@...fujitsu.com>,
Ingo Molnar <mingo@...e.hu>,
Pavel Emelyanov <xemul@...nvz.org>,
Jason Baron <jbaron@...hat.com>
Subject: Re: [patch 08/18] sched: add support for throttling group entities
On Mon, Aug 8, 2011 at 9:00 AM, Peter Zijlstra <a.p.zijlstra@...llo.nl> wrote:
> On Mon, 2011-08-08 at 23:46 +0800, Lin Ming wrote:
>> On Fri, Jul 22, 2011 at 12:43 AM, Paul Turner <pjt@...gle.com> wrote:
>>
>> > +static __used void throttle_cfs_rq(struct cfs_rq *cfs_rq)
>> > +{
>> > + struct rq *rq = rq_of(cfs_rq);
>> > + struct cfs_bandwidth *cfs_b = tg_cfs_bandwidth(cfs_rq->tg);
>> > + struct sched_entity *se;
>> > + long task_delta, dequeue = 1;
>> > +
>> > + se = cfs_rq->tg->se[cpu_of(rq_of(cfs_rq))];
>> > +
>> > + /* account load preceding throttle */
>> > + update_cfs_load(cfs_rq, 0);
>> > +
>> > + task_delta = cfs_rq->h_nr_running;
>> > + for_each_sched_entity(se) {
>> > + struct cfs_rq *qcfs_rq = cfs_rq_of(se);
>> > + /* throttled entity or throttle-on-deactivate */
>> > + if (!se->on_rq)
>> > + break;
>>
>> Does it mean it's possible that child se is unthrottled but parent se
>> is throttled?
>
> Yep..
>
>> I thought if parent group was throttled then its children should be
>> throttled too.
>> I may misunderstood the code, please correct me then.
>
> That would be costly, as throttling a parent would require throttling
> all its children (of which there can be arbitrary many).
>
In case it is not clear, the children of a throttled entity can not be
scheduled, they are implicitly throttled by virtue of their
parent/ancestor having reached its bandwidth limit (and being
throttled).
Consider the hierarchy below:
A
/ \
D B
\
C
If A and B both have bandwidth limits then B being on_rq depends on:
1. A being within its bandwidth limit, otherwise the entire hierarchy
would be dequeued
2. B being within its bandwidth limit, otherwise the hierarchy B-C
would be dequeued
B's throttle state is independent of whether A has reached its limit;
however it will not be runnable while A is throttled.
The per-cfs_rq throttle_count may be more directly in-line with what
your interpretation of "throttled"; it maintains explicit tracking of
whether or not an entity is throttled (including via its parent).
- Paul
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/
Powered by blists - more mailing lists