Re: [PATCH 11/14] irq: add support for allocating (and affinitizing) sets of IRQs

[Jens Axboe]

On 10/25/18 3:52 PM, Keith Busch wrote:
> On Thu, Oct 25, 2018 at 03:16:23PM -0600, Jens Axboe wrote:
>> A driver may have a need to allocate multiple sets of MSI/MSI-X
>> interrupts, and have them appropriately affinitized. Add support for
>> defining a number of sets in the irq_affinity structure, of varying
>> sizes, and get each set affinitized correctly across the machine.
> 
> <>
> 
>> @@ -258,13 +272,18 @@ int irq_calc_affinity_vectors(int minvec, int maxvec, 
>> const struct irq_affinity
>>  {
>>      int resv = affd->pre_vectors + affd->post_vectors;
>>      int vecs = maxvec - resv;
>> +    int i, set_vecs;
>>      int ret;
>>  
>>      if (resv > minvec)
>>              return 0;
>>  
>>      get_online_cpus();
>> -    ret = min_t(int, cpumask_weight(cpu_possible_mask), vecs) + resv;
>> +    ret = min_t(int, cpumask_weight(cpu_possible_mask), vecs);
>>      put_online_cpus();
>> -    return ret;
>> +
>> +    for (i = 0, set_vecs = 0;  i < affd->nr_sets; i++)
>> +            set_vecs += affd->sets[i];
>> +
>> +    return resv + max(ret, set_vecs);
>>  }
> 
> This is looking pretty good, but we may risk getting into an infinite
> loop in __pci_enable_msix_range() if we're requesting too many vectors
> in a set: the above code may continue returning set_vecs, overriding
> the reduced nvec that pci requested, and pci msix initialization will
> continue to fail because it is repeatedly requesting to activate the
> same vector count that failed before.

Good catch, we always want to be using min() with the passed in maxvec
in there. How about this incremental?


diff --git a/kernel/irq/affinity.c b/kernel/irq/affinity.c
index 0055e252e438..2046a0f0f0f1 100644
--- a/kernel/irq/affinity.c
+++ b/kernel/irq/affinity.c
@@ -272,18 +272,21 @@ int irq_calc_affinity_vectors(int minvec, int maxvec, 
const struct irq_affinity
 {
        int resv = affd->pre_vectors + affd->post_vectors;
        int vecs = maxvec - resv;
-       int i, set_vecs;
-       int ret;
+       int set_vecs;
 
        if (resv > minvec)
                return 0;
 
-       get_online_cpus();
-       ret = min_t(int, cpumask_weight(cpu_possible_mask), vecs);
-       put_online_cpus();
+       if (affd->nr_sets) {
+               int i;
 
-       for (i = 0, set_vecs = 0;  i < affd->nr_sets; i++)
-               set_vecs += affd->sets[i];
+               for (i = 0, set_vecs = 0;  i < affd->nr_sets; i++)
+                       set_vecs += affd->sets[i];
+       } else {
+               get_online_cpus();
+               set_vecs = cpumask_weight(cpu_possible_mask);
+               put_online_cpus();
+       }
 
-       return resv + max(ret, set_vecs);
+       return resv + min(set_vecs, vecs);
 }

-- 
Jens Axboe