On Sat, Jul 04, 2015 at 11:53:57AM +0200, Thomas Gleixner wrote: > On Sat, 4 Jul 2015, Russell King - ARM Linux wrote: > > > On Sat, Jul 04, 2015 at 01:19:30PM +0800, Jisheng Zhang wrote: > > > On Marvell Berlin SoCs, the cpu's local timer is shutdown when the cpu > > > goes to a deep idle state, then the timer framework will be notified to > > > use a broadcast timer instead. The broadcast timer uses dw-apb-ictl as > > > interrupt chip, this patch adds irq_set_affinity support so that the > > > going to deep idle state cpu can set the interrupt affinity of the > > > broadcast interrupt to avoid unnecessary wakeups and IPIs. > > > > NAK to this patch. > > > > The real question is - if CPU0 is the CPU going offline, why is it > > still receiving _any_ interrupts - all interrupts should be migrated > > off it, including the chained interrupts. > > > > Sounds like there's a bug in the migration code which needs further > > investigation, rather than hacking around the problem by introducing > > lots of driver code. > > I think you misunderstood the changelog, which is horrible btw. > > So the real reason to do this is to steer the broadcast interrupt to > the CPU which has the earliest expiry time. This avoids that another > cpu is woken from idle just to deliver the broadcast IPI to the other > cpu.
Unless I'm mistaken, the code does this by messing around with the parent interrupt affinity of a chained interrupt, which really isn't a good thing to do, because it migrates every interrupt on the child interrupt controller. -- FTTC broadband for 0.8mile line: currently at 10.5Mbps down 400kbps up according to speedtest.net. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
