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Re: tasklet latency and system calls on mips

To: Jun Sun <>
Subject: Re: tasklet latency and system calls on mips
From: "Sirotkin, Alexander" <>
Date: Mon, 18 Aug 2003 18:29:52 +0300
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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
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.


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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