On Wed, 2012-09-26 at 21:33 +0530, Srivatsa S. Bhat wrote: > I have some fundamental questions here: > 1. Why was the CPU never removed from the affinity masks in the original > code? I find it hard to believe that it was just an oversight, because the > whole point of fixup_irqs() is to affine the interrupts to other CPUs, IIUC. > So, is that really a bug or is the existing code correct for some reason > which I don't know of?
I am not aware of the history but my guess is that the affinity mask which is coming from the user-space wants to be preserved. And fixup_irqs() is fixing the underlying interrupt routing when the cpu goes down with a hope that things will be corrected when the cpu comes back online. But as Liu noted, we are not correcting the underlying routing when the cpu comes back online. I think we should fix that rather than modifying the user-specified affinity. > 2. In case this is indeed a bug, why are the warnings ratelimited when the > interrupts can't be affined to other CPUs? Are they not serious enough to > report? Put more strongly, why do we even silently return with a warning > instead of reporting that the CPU offline operation failed?? Is that because > we have come way too far in the hotplug sequence and we can't easily roll > back? Or are we still actually OK in that situation? Are you referring to the "cannot set affinity for irq" messages? That happens only if the irq chip doesn't have the irq_set_affinity() setup. But that is not common. > > Suresh, I'd be grateful if you could kindly throw some light on these > issues... I'm actually debugging an issue where an offline CPU gets apic timer > interrupts (and in one case, I even saw a device interrupt), which I have > reported in another thread at: https://lkml.org/lkml/2012/9/26/119 > But this issue in fixup_irqs() that Liu brought to light looks even more > surprising to me.. These issues look different to me, will look into that. thanks, suresh -- 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/
