From: Alex Shi <alex.shi@linaro.org>
To: Michael wang <wangyun@linux.vnet.ibm.com>,
mingo@redhat.com, peterz@infradead.org, tglx@linutronix.de,
daniel.lezcano@linaro.org, vincent.guittot@linaro.org,
morten.rasmussen@arm.com
Cc: linux-kernel@vger.kernel.org, akpm@linux-foundation.org,
fengguang.wu@intel.com, linaro-kernel@lists.linaro.org
Subject: Re: [RFC PATCH] sched: find the latest idle cpu
Date: Wed, 15 Jan 2014 22:28:10 +0800 [thread overview]
Message-ID: <52D69AFA.1060308@linaro.org> (raw)
In-Reply-To: <52D6412D.8050000@linux.vnet.ibm.com>
On 01/15/2014 04:05 PM, Michael wang wrote:
> On 01/15/2014 02:45 PM, Alex Shi wrote:
> [snip]
>>
>> yes, to save your scenario, we need to know the next timer for idle cpu,
>> but that is not enough, interrupt is totally unpredictable. So, I'd
>> rather bear the coarse method now.
>>>
>>> So what about just check 'ts->tick_stopped' and record one ticking idle
>>> cpu? the cost could be lower than time comparison, we could reduce the
>>> risk may be...(well, not so risky since the logical only works when
>>> system is relaxing with several cpu idle)
>>
>> first, nohz full also stop tick. second, tick_stopped can not reflect
>> the interrupt. when the idle cpu was interrupted, it's waken, then be a
>> good candidate for task running.
>
> IMHO, if we have to do gamble here, we better choose the cheaper bet,
> unless we could prove this 'coarse method' have more higher chance for
> BINGO than just check 'tick_stopped'...
Tick stopped on a nohz full CPU, but the cpu still had a task running...
>
> BTW, may be the logical should be in the select_idle_sibling()?
both of functions need to be considered.
>
> Regards,
> Michael Wang
>
>>
>
--
Thanks
Alex
next prev parent reply other threads:[~2014-01-15 14:28 UTC|newest]
Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-01-15 4:07 [RFC PATCH] sched: find the latest idle cpu Alex Shi
2014-01-15 4:31 ` Michael wang
2014-01-15 4:48 ` Alex Shi
2014-01-15 4:53 ` Alex Shi
2014-01-15 5:06 ` Alex Shi
2014-01-15 5:33 ` Michael wang
2014-01-15 6:45 ` Alex Shi
2014-01-15 8:05 ` Michael wang
2014-01-15 14:28 ` Alex Shi [this message]
2014-01-15 7:35 ` Peter Zijlstra
2014-01-15 14:37 ` Alex Shi
2014-01-16 11:03 ` Daniel Lezcano
2014-01-16 11:38 ` Peter Zijlstra
2014-01-16 12:16 ` Daniel Lezcano
2014-01-17 2:40 ` Nicolas Pitre
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