linux-kernel - One Interrupted Threads per Interrupt line?

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Date:	Sat, 4 Jun 2011 13:48:57 +0200
From:	Monica Puig-Pey <puigpeym@...can.es>
To:	<linux-rt-users@...r.kernel.org>, <linux-kernel@...r.kernel.org>
Subject: One Interrupted Threads per Interrupt line?

Hi,

I'm using Ubuntu 10.04 with the 2.6.31-11-rt patch installed. I'm 
developing a PCI device driver using hardware interrupts.
I read in the “Internals of the RT Patch” document 
(http://www.kernel.org/doc/ols/2007/ols2007v2-pages-161-172.pdf ) that 
when a device driver requests an IRQ, a thread is created to service 
this interrupt line (Threaded interrupts). Only ONE thread can be 
created per interrupt line, so shared interrupts are still handled by a 
single thread.

My driver requests IRQ 16, which is shared with others handlers. Typing 
on the shell  $ps -eo pid,pri,rtprio,cmd I can see my driver requesting 
irq 16 and with 50 RTPRIO. At the same time I can see the others drivers 
requesting IRQ 16 with different real time priorities than mine( 80, 85, 
50). Does this mean that there are more than ONE Threaded Interrupts for 
IRQ 16? or it's just the thread priority when running each handler for 
IRQ 16?
Finally, how could I change the 50 RT PRIO for my handler pci_9111?

Here you have the shell:

   PID PRI RTPRIO CMD

   658 120     80 [irq/16-uhci_hcd]
  3852 125     85 [irq/16-HDA Inte]
  4303  90     50 [irq/16-radeon@p]
  5863  90     50 [irq/16-pci_9111]
  5865  19      - ps -eo pid,pri,rtprio,cmd

Thank you very much,

Mónica
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