Re: Wake_up_process() in interrupt handler

[Bobby Sardana <sardana@obsoft.com>]

Greetings everyone:

Just curious, how is the bottom half declared & defined and where? In 
the application process space or in the kernel context? Some concrete 
brief examples would help.

regards,

Bobby Sardana.
sardana@obsoft.com

Raghu R. Arur wrote:

>  An interrupt handler has two parts .. one the top half which includes 
>the important tasks that are to be executed as soon as an interrupt occurs 
>and bottome half which are the instructions that are of less importance. 
>So when an interrupt occurs it executes the top half and returns to the 
>process that was executing. Then when the cpu is free or doing some less 
>important task like executing in the user space it will do the bottom half 
>job !!!!
>
>
>On Thu, 31 Oct 2002, Jan Hudec wrote:
>
>  
>
>>On Thu, Oct 31, 2002 at 01:01:27PM -0800, kernel_learner wrote:
>>    
>>
>>>  I am don' completely understand the concept of
>>>bottom_half...can you give me some pointers abuot
>>>that..
>>>      
>>>
>>I never needed it, so I don't know that much. And I don't recall where
>>I read about them. I think there is something about them in the Linux Kernel
>>Module Programming Guide and/or the Kernel Hacking Guide (both are a bit
>>obsolete, but the basic idea of four contexts did not change.
>>
>>There are four contexts - interrupt, bottom_half, process and userland
>>(the correct names are probably little different). Interrupt handlers
>>are run with interrupts disabled. They should be fast not to mask other
>>interrupts for too long. If more work has to be done, the interrupt
>>requires a bottom-half or tasklet (limited number of bottomhalves exist,
>>one is used to call tasklets, which are function pointers in a list).
>>Bottom-halves are called "as soon as possible and is safe", which in
>>practice is in context-switch AFAIK (ie. return to user-land or timer
>>interrupt (it calls schedule)). You can only sleep (ie. call schedule())
>>in process context which is syscalls and kernel threads and which is
>>associated with a process (has valid current), since scheduler works in
>>terms of processes.
>>
>>-------------------------------------------------------------------------------
>>						 Jan 'Bulb' Hudec <bulb@ucw.cz>
>>--
>>Kernelnewbies: Help each other learn about the Linux kernel.
>>Archive:       http://mail.nl.linux.org/kernelnewbies/
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>>
>>    
>>
>
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>  
>


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