Messages in this thread | | | Date | Mon, 30 Dec 2013 10:08:27 -0500 | From | Prarit Bhargava <> | Subject | Re: [PATCH] x86: Add check for number of available vectors before CPU down [v2] |
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On 12/30/2013 07:56 AM, rui wang wrote:
> An irq can be mapped to only one vector number, but can have multiple > destination CPUs. i.e. the same irq/vector can appear on multiple > CPUs' vector_irq[]. So checking data->affinity is necessary I think.
That's true Rui -- but here's what I think the scenario actually is.
Suppose we have a 4-cpu system, and we have an IRQ that is mapped to multiple cpu's vector_irq[]. For example, we have IRQ 200 that is mapped to CPU 2 vector_irq[50], and CPU 3 vector_irq[60].
Now I 'echo 0 > /sys/devices/system/cpu/cpu3/online'.
cpu_disable is called and the kernel migrates IRQs off to other cpus. Regardless if IRQ 200 is already mapped to CPU2 vector_irq[50], the mapping for CPU 3 vector_irq[60] *must be migrated* to another CPU. It has a valid irq handler and the IRQ is active. It doesn't just disappear because the CPU went down.
ie) AFAICT we should not differentiate between a multiple mapped IRQ and a singly mapped IRQ when traversing the vector_irq[] for CPU 3.
I'm probably being dense on this but I'm not seeing a problem with migrating the IRQ.
> But notice that data->affinity is updated in chip->irq_set_affinity() > inside fixup_irqs(), while cpu_online_mask is updated in > remove_cpu_from_maps() inside cpu_disable_common().
It shouldn't matter that the maps are updated in different areas during the execution as we're in stop_machine().
They are updated > in different places. So the algorithm to check them against each other > should be different, depending on where you put the check_vectors(). > That's my understanding. >
P.
> Thanks > Rui
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