On Mon, Mar 18, 2013 at 10:40:56PM +0800, chpoph wrote: > On Sun, Mar 17, 2013 at 08:05:43PM +0000, Will Deacon wrote: > >Do you actually have an ARM platform that can scale the CPU frequencies > independently? > > Yes, my smart phone use Qualcomm's 8x25 and 8064 platform, which can > scale the CPU frequencies independently. I test the delay loop, the > phone can't get accurate delayed time intervals.
That is expected. udelay() is only approximate. Sometimes, it will give you a slightly shorter delay than asked for, or if preempted, it can give you a much longer delay - because it has no idea how long it has been preempted for. This is why in a SMP system it is much better to use a timer-based udelay() implementation which is more independent of these effects. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
