On Mon, 2011-12-12 at 17:12 -0500, Alan Stern wrote: > How long is it okay to busy-wait with interrupts disabled? Are there > any clear-cut guidelines? > > My feeling is that for ordinary desktop use, 1-2 ms should be about the > limit, but other people may feel differently. (There's one spot in > ehci-hcd where the delay can last up to 250 ms, which does seem rather "250 ms", holy freaking OUCH! Batman! > excessive. Fortunately it never takes that long unless the hardware is > broken.) > > No doubt the RT people would say the upper bound should be on the order > of a few microseconds or less. I'd be happy to change ehci-hcd, which > has several delays in the 1-2 ms range -- but they tend to be nested > inside routines that are called within the scope of spinlock_irq, which > means a fair amount of rewriting would be needed. > > Any thoughts or recommendations? Note that in -rt, spinlocks are really mutexes (unless they are raw_spinlocks, which you shouldn't do). Thus, if your spin is with spinlock_irq, it wont affect -rt, as it will not have interrupts disabled. But I could imagine that such a long latency could manifest itself into something nasty (lots of interrupts queued up and such) that normal desktop users might see a hiccup or two. -- Steve -- 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
