linux-kernel - Re: [PATCH -V2] acpi: don't cond

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Message-ID: <4B227275.5010201@gmail.com>
Date:	Fri, 11 Dec 2009 19:25:25 +0300
From:	Alexey Starikovskiy <aystarik@...il.com>
To:	Pavel Machek <pavel@....cz>
CC:	Alexey Starikovskiy <astarikovskiy@...e.de>,
	Lin Ming <ming.m.lin@...el.com>,
	Xiaotian Feng <dfeng@...hat.com>,
	"linux-acpi@...r.kernel.org" <linux-acpi@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Len Brown <lenb@...nel.org>,
	"Moore, Robert" <robert.moore@...el.com>
Subject: Re: [PATCH -V2] acpi: don't cond_resched if irq is disabled

Pavel Machek пишет:
> On Fri 2009-12-11 14:48:21, Alexey Starikovskiy wrote:
>   
>> Lin Ming ??????????:
>>     
>>> On Thu, 2009-12-10 at 20:21 +0800, Alexey Starikovskiy wrote:
>>>       
>>>> Hi Xiaotian,
>>>>
>>>> I think, this is another round of "armor vs. bullet" race... It will hold until
>>>> might_sleep() logic changes again.
>>>>
>>>> Please consider using preemptible() -- IMHO this is the check we should perform 
>>>> in our case of voluntary preemption.
>>>>         
>>> preemptible() may not work here because it always returns 0 for
>>> non-preemptible kernel.
>>>       
>> Right, and it means that this machine does not care about low latency that much.
>> The reason we introduced the preemption point in the first place, was unacceptable latency
>> due to very long AML methods on some machines. We don't need this preemption point for normal
>> operation, this is exactly what voluntary preemption does -- allows those in hurry to pass by.
>> If there are none, fine.
>>     
>>> #ifdef CONFIG_PREEMPT
>>> # define preemptible()  (preempt_count() == 0 && !irqs_disabled())
>>> # define IRQ_EXIT_OFFSET (HARDIRQ_OFFSET-1)
>>> #else
>>> # define preemptible()  0
>>> # define IRQ_EXIT_OFFSET HARDIRQ_OFFSET
>>> #endif
>>>       
>
> Well, normally we want low latency even for !CONFIG_PREEMPT kernels.
>
> Actually, explicit preemption points are NOPs for CONFIG_PREEMPT
> kernels, right?
> 									Pavel
>   
Right. Do you have code?

Thanks,
Alex.
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