linux-kernel - Re: [PATCH] sched_rt: Removes extra checking for nr_cpus_allowed when calling find_lowest

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Message-ID: <AANLkTiku=BcJBQx5Av=Ri+Cd4b+VFY_Y2NL2sd4iQxLM@mail.gmail.com>
Date:	Tue, 19 Oct 2010 17:12:06 +0600
From:	Rakib Mullick <rakib.mullick@...il.com>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	LKML <linux-kernel@...r.kernel.org>, Ingo Molnar <mingo@...e.hu>,
	Steven Rostedt <rostedt@...dmis.org>,
	Gregory Haskins <ghaskins@...ell.com>
Subject: Re: [PATCH] sched_rt: Removes extra checking for nr_cpus_allowed when
 calling find_lowest_rq

On Tue, Oct 19, 2010 at 5:02 PM, Peter Zijlstra <peterz@...radead.org> wrote:
> On Tue, 2010-10-19 at 16:57 +0600, Rakib Mullick wrote:
>> sched_rt: Removes extra checking for nr_cpus_allowed when calling
>> find_lowest_rq
>
> Why repeat this subject?

Just trying to give a good looking format :-). Not sure whether it
really is or not.
>
>
> That's just not explaining anything.. what can go wrong, how does this
> fix it.

Actually it's not a fix. It just removes a check. It checks whether
this process is movable to other processor or not. And this check is
made from inside the find_lowest_cpu function. Thats why, the check
before calling find_lowest_cpu has been removed. Is my explanation
okay?

Thanks,
Rakib


>
>> Signed-off-by: Rakib Mullick <rakib.mullick@...il.com>
>> ---
>>
>> --- linus-rc8/kernel/sched_rt.c       2010-10-15 05:26:43.000000000 +0600
>> +++ rakib-rc8/kernel/sched_rt.c       2010-10-19 16:22:30.000000000 +0600
>> @@ -971,8 +971,7 @@ select_task_rq_rt(struct rq *rq, struct
>>        * that is just being woken and probably will have
>>        * cold cache anyway.
>>        */
>> -     if (unlikely(rt_task(rq->curr)) &&
>> -         (p->rt.nr_cpus_allowed > 1)) {
>> +     if (unlikely(rt_task(rq->curr))) {
>>               int cpu = find_lowest_rq(p);
>>
>>               return (cpu == -1) ? task_cpu(p) : cpu;
>
>
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