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

[Preeti U Murthy <preeti@linux.vnet.ibm.com>]

On 01/16/2013 05:32 PM, Ivo Sieben wrote:
> 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)
> 
Fair enough Ivo.I think you should go ahead with merging the
waitqueue_active()
  wake_up()
logic into the wake_up() variants.

Regards
Preeti U Murthy