Re: [PATCH] tty: Only wakeup the line discipline idle queue when queue is active

Ivo Sieben
2013-01-16T12:02:53Z

2013/1/16 Preeti U Murthy <preeti@linux.vnet.ibm.com>:
>
> Yes.Thank you very much for the explanation :) But I dont see how the
> context switching goes away with your patch.With your patch, when the
> higher priority thread comes in when the lower priority thread is
> running in the critical section,it will see the wait queue empty and
> "continue its execution" without now wanting to enter the critical
> section.So this means it will preempt the lower priority thread because
> it is not waiting on a lock anyway.There is a context switch here right?
> I dont see any problem in scheduling due to this,but I do think your
> patch is essential.
>

I don't have a problem that there is a context switch to the high
priority process: it has a higher priority, so it probably is more
important.
My problem is that even when the waitqueue is empty, the high priority
thread has a risk to block on the spinlock needlessly (causing context
switches to low priority task and back to the high priority task)

Regards,
Ivo Sieben