Re: Regarding ISR stack

[Thomas Petazzoni <thomas.petazzoni@xxxxxxxx>]

Hi,

Le Fri, 2 Feb 2007 12:15:46 +0530,
"Pharaoh ." <pharaoh137@xxxxxxxxx> a écrit :

> I have read some where recently that an ISR can have separate stack
> also i.e. an ISR need not share the stack of interrupted process.
> What I was thinking till now is, an ISR shares the stack of the
> process which was executing when the interrupt occured and ISR got
> invoked, thats why things are in fragile state when ISR is executing.
> 
> My question is:
> 
> Is it true that, an ISR can have seperate stack? If yes then please
> provide me pointers/link to the details. if no then why not? Won't
> life be easier if the ISR have their own stacks? I know may be this
> is not feasible on machines with less memory.

It depends on whether you have CONFIG_4KSTACKS or not.

If it's not defined, then you have 8k stacks for each thread, and the
stack of a thread is used during the execution of the ISR that
interrupted its execution.

If it's defined, then you have 4k stacks for each thread, and a
separate stack to handle the ISRs.

On i386, CONFIG_4KSTACKS doesn't seem to be the default (according to
arch/i386/defconfig).

Regarding memory consumption, 4k stacks are certainly better than 8k
stacks, see http://lwn.net/Articles/63516/. And it avoids 1-order
allocations, which can be difficult under memory pressure.

For more informations:
 http://lwn.net/Articles/84583/
 http://lwn.net/Articles/150580/
 http://lwn.net/Articles/160138/

Sincerly,

Thomas
-- 
Thomas Petazzoni - thomas.petazzoni@xxxxxxxx
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http://www.{livret,agenda}dulibre.org

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