Uwe Kleine-König <u.kleine-koenig <at> pengutronix.de> writes: > > IRQ thread, then use sys_sched_setscheduler(pid,...) to change its priority. > > I'll try that out in the morning. > I wouldn't recommend calling sys_sched_setscheduler from kernel space. > That's the userspace API and you need to pass a __user pointer as third > argument. Good point, although my ioctl() will be passing the scheduling parameters from user-space. So the need for a __user pointer for this would not be a problem. Alternatively one could call task_setprio(), instead of sys_sched_setscheduler(), and omit the then reduntant step of figuring out the PID of the task. > The right way is to do this change from userspace. Which is what I am trying to do. I want the application thread that uses my driver to be able to set the priority of its interrupt to equal the priority of the calling thread. The problem with calling sched_setscheduler directly from user-space, is figuring out the PID of the IRQ thread. First of all, I have multiple boards of the same type, such that looking in /proc/interrupts won't tell me which IRQ is being used by a given board. So I would have to implement an ioctl() anyway, just to query the IRQ from the device driver. Secondly, the PID of the corresponding IRQ thread changes each time that request_irq() is called, and then later freed. So searching for the IRQ thread couldn't be done by a wrapper script around the program. It seems much more friendly and efficient for my driver to provide applications with an ioctl that tells it to set the priority of its IRQ thread. Note that none of this would be necessary if the IRQ thread of a device automatically inherited the priority of the highest priority realtime thread that has requested (and not yet free'd) its IRQ. Not doing so, leads to a form of priority inversion. Thanks, Martin -- To unsubscribe from this list: send the line "unsubscribe linux-rt-users" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
