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List:       linux-arm-kernel
Subject:    Re: Preempt Real-Time for ARM
From:       "Eugeny S. Mints" <emints () ru ! mvista ! com>
Date:       2005-03-01 9:25:19
Message-ID: 422434FF.3090104 () ru ! mvista ! com
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Andreas Orfanos wrote:
> I think, SA_NODELAY might be confusing. SA_INT_RTLATENCY?

Most probably you are confused - SA_NODELAY runs an interrupt handler 
_not_ in a thread (but in interrupt context) even if threaded hardirqs 
feature is configured (separately or as part of PREEMPT_RT). IMO the 
name is quite straightforward though may be SA_NOTHREAD may be more 
meaningful. But not SA_INT_RTLATENCY.

	Eugeny
> 
> My point is that, ARM Linux kernel shouldn't diverse much from
> Linus kernel baseline. These enhancements might be very useful for 
> certain applications, but might have side effects on Linux stability.
> 
> I am guessing that light GUIs and small apps can run fine, but
> with high end GUI (X11+apps) on and a mini hard disk you 
> might see your file system damaged, or other funy things.
> 
> 
> 
> 
> 
> 
> On 28 Feb 2005 15:25:52 -0800, Daniel Walker <dwalker@mvista.com> wrote:
> 
>>On Mon, 2005-02-28 at 15:15, Russell King - ARM Linux wrote:
>>
>>>On Mon, Feb 28, 2005 at 10:49:08PM +0000, Andreas Orfanos wrote:
>>>
>>>>Is this new mechanism going to change the interrupt response?
>>>
>>>It will increase the interrupt latency, because not only do you have to
>>>receive the interrupt, you have to mark the interrupt thread runnable,
>>>perform a context switch, and run the interrupt.
>>
>>The SA_NODELAY flag is used to by bypass that, so if your interrupt
>>needs to run with no delay it can. Any no delay interrupt runs just like
>>in the normal kernel non-RT kernel.
>>
>>Russell is right otherwise. Most interrupt are converted into RT threads
>>so they can be preempted.
>>
>>
>>Daniel
>>
>>
> 
> 
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