Kernel code interrupted by Timer

[Peter Teoh]

On Sat, Feb 9, 2013 at 8:08 AM, Peter Teoh <htmldeveloper at gmail.com> wrote:

>
>
> On Sat, Feb 9, 2013 at 1:08 AM, Gaurav Jain <gjainroorkee at gmail.com>wrote:
>
>> What happens if the kernel executing in some process context (let's say
>> executing a time-consuming syscall) gets interrupted by the Timer - which
>> is apparently allowed in 2.6 onwards kernels.
>>
>> My understanding is that once the interrupt handler is done executing, we
>> should switch back to where the kernel code was executing. Specifically,
>> the interrupt handler for the Timer interrupt should not schedule some
>> other task since that might leave kernel data in an inconsistent state -
>> kernel didn't finish doing whatever it was doing when interrupted.
>>
>
> at the microscopic level, every stream of assembly instructions can always
> be broken up and intercepted by interrupt, and possibly switched into
> another stream of assembly instruction or logic, the maintenance of state
> "consistency" is done via context switching.
>

context switching is done at software level, and i am not if there is
difference between process context switch or thread/task level context
switching, but hardware only guarantee register context switch - and not
sure if it covers all the floating point (SSE) registers too (unlikely,
performance overheads)....so.."consistency" is really how you write your
software.   and u also have multiple switching (by different CPU) all
taking place independently all the time, writing into the same piece of RAM.

I also know that nvidia GPU does not clean up its memory/state when
switching from one process to another process, but that is beyond the
control of hardware switching logic of the CPU anyway.


>
>> So, does the Timer interrupt handler include such a policy for the above
>> case?
>>
>> --
>> Gaurav Jain
>>
>>
>>
>>
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>>
>>
>
>
> --
> Regards,
> Peter Teoh




-- 
Regards,
Peter Teoh
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