linux-kernel - Re: [PATCH V2 3/3] sched: Move idle

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Date:	Thu, 13 Feb 2014 15:44:18 +0530
From:	Preeti U Murthy <preeti@...ux.vnet.ibm.com>
To:	Daniel Lezcano <daniel.lezcano@...aro.org>
CC:	Preeti Murthy <preeti.lkml@...il.com>,
	Peter Zijlstra <peterz@...radead.org>, mingo@...nel.org,
	alex.shi@...aro.org, LKML <linux-kernel@...r.kernel.org>,
	Lists linaro-kernel <linaro-kernel@...ts.linaro.org>
Subject: Re: [PATCH V2 3/3] sched: Move idle_stamp up to the core

Hi Daniel,

On 02/11/2014 05:37 PM, Daniel Lezcano wrote:
> On 02/10/2014 11:04 AM, Preeti Murthy wrote:
>> Hi Daniel,
>>
>> On Fri, Feb 7, 2014 at 4:40 AM, Daniel Lezcano
>> <daniel.lezcano@...aro.org> wrote:
>>> The idle_balance modifies the idle_stamp field of the rq, making this
>>> information to be shared across core.c and fair.c. As we can know if the
>>> cpu is going to idle or not with the previous patch, let's
>>> encapsulate the
>>> idle_stamp information in core.c by moving it up to the caller. The
>>> idle_balance function returns true in case a balancing occured and
>>> the cpu
>>> won't be idle, false if no balance happened and the cpu is going idle.
>>>
>>> Cc: mingo@...nel.org
>>> Cc: alex.shi@...aro.org
>>> Cc: peterz@...radead.org
>>> Signed-off-by: Daniel Lezcano <daniel.lezcano@...aro.org>
>>> Signed-off-by: Peter Zijlstra <peterz@...radead.org>
>>> ---
>>>   kernel/sched/core.c  |   13 +++++++++++--
>>>   kernel/sched/fair.c  |   14 ++++++--------
>>>   kernel/sched/sched.h |    8 +-------
>>>   3 files changed, 18 insertions(+), 17 deletions(-)
>>>
>>> diff --git a/kernel/sched/core.c b/kernel/sched/core.c
>>> index 16b97dd..428ee4c 100644
>>> --- a/kernel/sched/core.c
>>> +++ b/kernel/sched/core.c
>>> @@ -2704,8 +2704,17 @@ need_resched:
>>>
>>>          pre_schedule(rq, prev);
>>>
>>> -       if (unlikely(!rq->nr_running))
>>> -               idle_balance(rq);
>>> +#ifdef CONFIG_SMP
>>> +       if (unlikely(!rq->nr_running)) {
>>> +               /*
>>> +                * We must set idle_stamp _before_ calling
>>> idle_balance(), such
>>> +                * that we measure the duration of idle_balance() as
>>> idle time.
>>
>> Should not this be "such that we *do not* measure the duration of
>> idle_balance()
>> as idle time?"
> 
> Actually, the initial code was including the idle balance time
> processing in the idle stamp. When I moved the idle stamp in core.c,
> idle balance was no longer measured (an unwanted change). That has been
> fixed and to prevent that to occur again, we added a comment.

Oh sorry! Yes you are right.

Thanks

Regards
Preeti U Murthy
> 

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