linux-kernel - Re: [PATCH 01/10] sched: select_task_rq

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Message-ID: <CAFTL4hyfxXcrgn2WZimoeH0FmNYJ1ZubnD2KM1S6GWVAbymEyA@mail.gmail.com>
Date:	Fri, 7 Dec 2012 02:02:37 +0100
From:	Frederic Weisbecker <fweisbec@...il.com>
To:	Alex Shi <alex.shi@...el.com>
Cc:	npiggin@...nel.dk, mingo@...hat.com, peterz@...radead.org,
	linux-kernel@...r.kernel.org, akpm@...ux-foundation.org,
	Mike Galbraith <efault@....de>
Subject: Re: [PATCH 01/10] sched: select_task_rq_fair clean up

2012/12/7 Alex Shi <alex.shi@...el.com>:
> On 12/07/2012 01:50 AM, Frederic Weisbecker wrote:
>> 2012/12/3 Alex Shi <alex.shi@...el.com>:
>>> It is impossible to miss a task allowed cpu in a eligible group.
>>>
>>> And since find_idlest_group only return a different group which
>>> excludes old cpu, it's also imporissible to find a new cpu same as old
>>> cpu.
>>
>> Is it possible for weighted_cpuload() to return ULONG_MAX? If so,
>> find_idlest_cpu() can return -1.
>>
>
> No, non of sched entity can has a ULONG_MAX weight.

Ok. find_idlest_cpu() can still return -1 but select_task_rq_fair() is
the only caller. Presumably safe but code evolves. May be add some
comment to explain why what you're doing is safe. May be a
WARN_ON_ONCE() could be good to add?
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