Dear Thomas, On Sat, 4 Jul 2015 14:49:31 +0200 Thomas Gleixner <t...@linutronix.de> wrote:
> On Sat, 4 Jul 2015, Russell King - ARM Linux wrote: > > 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. > > Fair enough, I missed that chained hackery. > > For that powersaving scenario it's probably ok to move the all child > irqs around, but we should at least make that an opt-in behaviour and > not enabled by default. Thank you for your suggestion. Is is acceptable to make an config option such as DW_APB_ICTL_SET_AFFINITY, and warn enabled this would migrates every interrupt, and disable it by default? Thanks a lot, Jisheng -- 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/
