Hi Martin,
> Is there a way for a device driver to set the priority of the
> IRQ thread that services interrupts from its hardware? I am
> writing a device driver for a digital I/O board with general
> purpose interrupt capability, and I would like the
> application to be able to tell the driver what priority it
> needs those interrupts to be given.
>
> Currently it appears that preemp_rt spawns all IRQ threads
> with priority 50, and that the only way to change the
> priority of an IRQ is for an application program to execute
> the chrt program, after the IRQ thread has been created.
> However this requires that the driver pass back information
> to the calling program about which IRQ it is using, so that
> the program can then call popen to first search for the PID
> of the corresponding thread, and then execute chrt to change
> its priority. This is possible but messy, and relies on the
> name of IRQ threads not changing in the future.
>
> So is there a way for driver code in the kernel to identify
> the thread of a given IRQ, and then change its priority?
I tried this exercise in a driver for 2.6.26. I succeeded in identifying the
thread for IRQ and its priority. I couldn't do the priority changes.
#if 1
struct sched_param param = { 0, };
struct irq_desc *desc;
// 2. Raise the priority of ISR thread
param.sched_priority = 90;
// get IRQ descriptor from IRQ, it contains pid
desc = &irq_desc[IRQ_BASIC_TIMER_3_1];
printk("Thread Priority = %u\n", desc->thread->prio);
#endif
Along with this, some minor changes ('static' to 'extern' etc) for irq_desc
structure in corresponding files.
For changing the priority, you may try patches sent by Remy Bohmer
[linux@xxxxxxxxxx] on 28-May.
-Suresh
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