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SubjectRe: [PATCH v3 2/2] irqchip/gic-v3-its: Balance initial LPI affinity across CPUs
From
Date
>>
>>> +        int this_count = its_read_lpi_count(d, tmp);
>>
>> Not sure if it's intentional, but now there seems to be a subtle
>> difference to what Thomas described for non-managed interrupts - for
>> non-managed interrupts, x86 selects the CPU based on the total
>> interrupt load per CPU (or, more specifically, lowest vector
>> allocation count), and not just the non-managed load. Or maybe I
>> misread it.
>
> So far, I'm trying to keep the two allocation paths separate, as the
> two systems I have access to have very different behaviours: D05 has
> no managed interrupts to speak of, and my top-secret work machine
> has almost no unmanaged interrupts, so the two sets are almost
> completely disjoint.

Sure, but I'd say that it would be a more common scenario to have a
mixture of both.

>
> Also, it all depends on the interrupt allocation order, and whether
> something will rebalance the non-managed interrupts at a later time.
> At least, these two patches make it easy to alter the placement policy
> (the behaviour you describe above is a 2 line change).
>
>> Anyway, we can test this now for NVMe with its managed interrupts.
>
> Looking forward to hearing from you!
>

On my D06CS board (128 core), there seems to be something wrong, as the
q0 affinity mask looks incorrect:

PCI name is 81:00.0: nvme0n1


irq 322, cpu list 69, effective list 69


irq 325, cpu list 32-38, effective list 32


irq 326, cpu list 39-45, effective list 40


irq 327, cpu list 46-51, effective list 47


irq 328, cpu list 52-57, effective list 53


irq 329, cpu list 58-63, effective list 59


And something stranger for my colleague Luo Jiaxing, specifically the
effective affinity:

PCI name is 85:00.0: nvme2n1
irq 196, cpu list 0-31, effective list 82
irq 377, cpu list 32-38, effective list 32
irq 378, cpu list 39-45, effective list 39
irq 379, cpu list 46-51, effective list 46

But then v5.6-rc5 vanilla also looks to have this issue when I tested on
my board:

john@ubuntu:~$ more /proc/irq/322/smp_affinity_list


69

My D06ES (96 core) board looks sensible for the affinity in this regard
(I did not try vanilla v5.6-rc5, but only with your patches on top).
I'll need to debug this.

Cheers,
John




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