ISR Timing

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Hi All
I am facing the strange problem.

We are uing the PPC Linux over the MPC860 Board. There is a kernel char
driver which interracts with the HW on request from the User Mode
Application. ISR routines are written in Kernel which sends the signal
to the User Mode using the Select poll mechanism.

When I put the printk inside the ISR routine , User Mode Task receives
the event very fast however on removing the printk it takes a long time
for the event to be recieved by the user task.

Can somebody help what the printk is doing ?

I have Level triggered interrupts and interrupts are disabled in ISR
and enabled on reading the HW source.

Thanks in Advance

Re: ISR Timing
First, it is a bad idea to use printk() inside an isr. You really cannot
trust any timing the results and you risk the system being locked up. An isr
runs with the rest of the kernel shut off. You can get some basic debugging
done that way. A much better way would be to use a trace mechanism.

Having said that, Let's go to your problem. It is hard to analyze anything
without seeing source code. You could email it if you don't feel comfortable
posting it. If it is large, you really can't post it here. There will be a
fairly simple solution. We just have to find it.


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