[RFC PATCH 0/4] USB: HCD/EHCI: giveback of URB in tasklet context

[Alan Stern]

On Fri, 14 Jun 2013, Ming Lei wrote:

> On Fri, Jun 14, 2013 at 3:41 AM, Alan Stern <stern at rowland.harvard.edu> wrote:
> >
> > The main reason for moving away from the current scheme is to reduce
> > latency for other interrupt handlers.  Ming gave two examples of slow
> > USB code that runs in hardirq context now; with his change they would
> > run in softirq context and therefore wouldn't delay other interrupts so
> > much.  (Interrupt latency is hard to measure, however.)
> 
> 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.

Alan Stern