On 12/20/2013 04:41 AM, rui wang wrote: > On 12/20/13, Prarit Bhargava <[email protected]> wrote: >> >> >> On 12/19/2013 01:05 PM, Tony Luck wrote: >>> On Wed, Dec 18, 2013 at 11:50 AM, Tony Luck <[email protected]> wrote: >>>> Looks good to me. >>> >>> Though now I've been confused by an offline question about affinity. >> >> Heh :) I'm pursuing it now. Rui has asked a pretty good question that I >> don't >> know the answer to off the top of my head. I'm still looking at the code. >> >>> >>> Suppose we have some interrupt that has affinity to multiple cpus. E.g. >>> (real example from one of my machines): >>> >>> # cat /proc/irq/94/smp_affinity_list >>> 26,54 >>> >>> Now If I want to take either cpu26 or cpu54 offline - I'm guessing that I >>> don't >>> really need to find a new home for vector 94 - because the other one of >>> that >>> pair already has that set up. But your check_vectors code doesn't look >>> like >>> it accounts for that - if we take cpu26 offline - it would see that >>> cpu54 doesn't >>> have 94 free - but doesn't check that it is for the same interrupt. >>> >>> But I may be mixing "vectors" and "irqs" here. >> >> Yep. The question really is this: is the irq mapped to a single vector or >> multiple vectors. (I think) >> > > The vector number for an irq is programmed in the LSB of the IOAPIC > IRTE (or MSI data register in the case of MSI/MSIx). So there can be > only one vector number (although multiple CPUs can be specified > through DM). An MSI-capable device can dynamically change the lower > few bits in the LSB to signal multiple interrupts with a contiguous > range of vectors in powers of 2,but each of these vectors is treated > as a separate IRQ. i.e. each of them has a separate irq desc, or a > separate line in the /proc/interrupt file. This patch shows the MSI > irq allocation in detail: > http://git.kernel.org/cgit/linux/kernel/git/tip/tip.git/commit/?id=51906e779f2b13b38f8153774c4c7163d412ffd9 >
Yep, that's where I got the idea for the affinity check in my previous post. So far linux.git top-of-tree + my patch looks good. I'm pulling down linux-next.git right now ... P. > Thanks > Rui > > >> P. >> >>> >>> -Tony >> -- >> 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/ >> -- 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/
