Re: tasklet latency and system calls on mips

["Sirotkin, Alexander" <demiurg@ti.com>]

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Jun Sun wrote:


On Thu, Aug 14, 2003 at 12:17:52PM +0300, Sirotkin, Alexander wrote:

  

I suspect that what happens is as follows :



system call arrives and while it's being processed and interrupt to one

of the drivers arrives. This interrupt 

schedules a tasklet which however is not executed after the system call

finishes, 

    



The tasklet should be executed at the return of interrupt handling.

If not, there is a bug.

  

I have a feeling that we are going in circles. Tasklets are executed at
the return of interrupt handler.
However, I suspect that this is not enough. On mips (contrary to x86),
system call is NOT an interrupt.
It's a different exception with different handler. Therefore I suspect
that tasklets are NOT called at 
the end of system call exception handler (which is a different handler,
not do_IRQ).






  

only after the next timer

interrupt which causes up to 10 ms latency (not all the time, only when

somebody makes a system call).



    



BTW, make sure tasklet_schedule() is indeed called in an interrupt
handler.

I am not sure why will happen otherwise.



If you suspect it is a bug, you can easily trace them.  You may my

little tracing tool useful,

I can try to trace it, I just wanted to ensure that what I was saying
makes sense. See above.






	
http://linux.junsun.net/patches/generic/experimental/030716.a-jstrace.pa
tch
<http://linux.junsun.net/patches/generic/experimental/030716.a-jstrace.p
atch> 



Jun

  


-- 

Alexander Sirotkin

SW Engineer



Texas Instruments

Broadband Communications Israel (BCIL)

Tel:  +972-9-9706587

________________________________________________________________________

"Those who do not understand Unix are condemned to reinvent it, poorly."

      -- Henry Spencer 

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