Messages in this thread | | | Date | Mon, 30 Dec 2013 20:56:01 +0800 | Subject | Re: [PATCH] x86: Add check for number of available vectors before CPU down [v2] | From | rui wang <> |
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On 12/29/13, Prarit Bhargava <prarit@redhat.com> wrote: > > > On 12/20/2013 04:41 AM, rui wang wrote: <<snip>> >> 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 >> >> Thanks >> Rui >> > > Gong and Rui, > > After looking at this in detail I realized I made a mistake in my patch by > including the check for the smp_affinity. Simply put, it shouldn't be > there > given Rui's explanation above. > > So I think the patch simply needs to do: > > this_count = 0; > for (vector = FIRST_EXTERNAL_VECTOR; vector < NR_VECTORS; vector++) > { > irq = __this_cpu_read(vector_irq[vector]); > if (irq >= 0) { > desc = irq_to_desc(irq); > data = irq_desc_get_irq_data(desc); > affinity = data->affinity; > if (irq_has_action(irq) && !irqd_is_per_cpu(data)) > this_count++; > } > } > > Can the two of you confirm the above is correct? It would be greatly > appreciated.
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. 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(). 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.
Thanks Rui
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