On Fri, 14 Jun 2013, Ming Lei wrote: > >> With the two trace points of irq_handler_entry and irq_handler_exit, the > >> interrupt latency(or the time taken by hard irq handler) isn't hard to measure. > >> One simple script can figure out the average/maximum latency for one irq > >> handler, like I did in 4/4. > > > > But that doesn't measure the time between when the IRQ request is > > issued and when irq_handler_entry runs. > > That might be hard to measure, also I am wondering if the time can be > measured only by software, but these patches only focus on the time > between HCD irq entry and irq exit. Not entirely. On a UP system, leaving interrupts disabled for a long time (which is what we do now) increases the delay between when the IRQ is raised and when it is serviced. On an SMP system, a long-running interrupt handler will delay servicing a different device that shares the same IRQ line. Alan Stern -- To unsubscribe from this list: send the line "unsubscribe linux-usb" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
