On Tue, 16 Feb 2016, David Daney wrote: > On 02/15/2016 07:45 AM, Ioan Nicu wrote: > > Octeon sets the default irq affinity to value 1 in the early arch init > > code, so by default all irqs get registered with their affinity set to > > core 0. > > > > When setting one CPU ofline, octeon_irq_cpu_offline_ciu() calls > > irq_set_affinity_locked(), but this function sets the IRQD_AFFINITY_SET bit > > in the irq descriptor. This has the side effect that if one irq is > > requested later, after putting one CPU offline, the affinity of this irq > > would not be the default anymore, but rather forced to "all cores - the > > offline core". > > > > This patch sets the IRQCHIP_ONOFFLINE_ENABLED flag in octeon irq > > controllers, so that the kernel would call the irq_cpu_[on|off]line() > > callbacks only for enabled irqs. If some other irq is requested after > > setting one cpu offline, it would use the default irq affinity, same as it > > would do in the normal case where there is no CPU hotplug operation. > > > > Signed-off-by: Ioan Nicu <ioan.nicu.ext@xxxxxxxxx> > > Acked-by: Alexander Sverdlin <alexander.sverdlin@xxxxxxxxx> > > In principle, I don't object. > > I would like to see what tglx has to say about this though. If we are > worried about the IRQD_AFFINITY_SET bit, I am not convinced that this is the > best place to be tweaking code. Are we papering over something that should > be handled in a more general manner? I don't know. Hmm. Good question. We probably should not set IRQD_AFFINITY_SET when called from the offline code. The flag was originally meant to preserve user space affinity settings across request/free_irq. Though it gets set via irq_set_affinity() as well and therefor via irq_set_affinity_locked(). Now we could move that IRQD_AFFINITY_SET flip to the user space interface, but we have to look at all the kernel internal call sites of irq_set_affinity() and irq_set_affinity_locked() whether any of those relies on affinity settings being preserved. irq_set_affinity_locked() probably not, as the only non core user is the octeon code, but you probably can answer that question :) Thanks, tglx
