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

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Message-ID: <52FA1270.9020806@linaro.org>
Date:	Tue, 11 Feb 2014 13:07:12 +0100
From:	Daniel Lezcano <daniel.lezcano@...aro.org>
To:	Preeti Murthy <preeti.lkml@...il.com>
CC:	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>,
	Preeti U Murthy <preeti@...ux.vnet.ibm.com>
Subject: Re: [PATCH V2 3/3] sched: Move idle_stamp up to the core

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.

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