Re: [PATCH V5 net-next] net: mana: Assigning IRQ affinity on HT cores

[Yury Norov]

Few more nits

On Fri, Dec 08, 2023 at 06:03:40AM -0800, Yury Norov wrote:
> On Fri, Dec 08, 2023 at 02:02:34AM -0800, Souradeep Chakrabarti wrote:
> > Existing MANA design assigns IRQ to every CPU, including sibling
> > hyper-threads. This may cause multiple IRQs to be active simultaneously
> > in the same core and may reduce the network performance with RSS.
> 
> Can you add an IRQ distribution diagram to compare before/after
> behavior, similarly to what I did in the other email?
> 
> > Improve the performance by assigning IRQ to non sibling CPUs in local
> > NUMA node. The performance improvement we are getting using ntttcp with
> > following patch is around 15 percent with existing design and approximately
> > 11 percent, when trying to assign one IRQ in each core across NUMA nodes,
> > if enough cores are present.
> 
> How did you measure it? In the other email you said you used perf, can
> you show your procedure in details?
> 
> > Suggested-by: Yury Norov <yury.norov@xxxxxxxxx>
> > Signed-off-by: Souradeep Chakrabarti <schakrabarti@xxxxxxxxxxxxxxxxxxx>
> > ---
> 
> [...]
> 
> >  .../net/ethernet/microsoft/mana/gdma_main.c   | 92 +++++++++++++++++--
> >  1 file changed, 83 insertions(+), 9 deletions(-)
> > 
> > diff --git a/drivers/net/ethernet/microsoft/mana/gdma_main.c b/drivers/net/ethernet/microsoft/mana/gdma_main.c
> > index 6367de0c2c2e..18e8908c5d29 100644
> > --- a/drivers/net/ethernet/microsoft/mana/gdma_main.c
> > +++ b/drivers/net/ethernet/microsoft/mana/gdma_main.c
> > @@ -1243,15 +1243,56 @@ void mana_gd_free_res_map(struct gdma_resource *r)
> >  	r->size = 0;
> >  }
> >  
> > +static int irq_setup(int *irqs, int nvec, int start_numa_node)
> > +{
> > +	int w, cnt, cpu, err = 0, i = 0;
> > +	int next_node = start_numa_node;
> 
> What for this?
> 
> > +	const struct cpumask *next, *prev = cpu_none_mask;
> > +	cpumask_var_t curr, cpus;
> > +
> > +	if (!zalloc_cpumask_var(&curr, GFP_KERNEL)) {

alloc_cpumask_var() here and below, because you initialize them by
copying

> > +		err = -ENOMEM;
> > +		return err;
> > +	}
> > +	if (!zalloc_cpumask_var(&cpus, GFP_KERNEL)) {
> 
>                 free(curr);
> 
> > +		err = -ENOMEM;
> > +		return err;
> > +	}
> > +
> > +	rcu_read_lock();
> > +	for_each_numa_hop_mask(next, next_node) {
> > +		cpumask_andnot(curr, next, prev);
> > +		for (w = cpumask_weight(curr), cnt = 0; cnt < w; ) {

OK, if you can't increment inside for-loop, I'd switch it to a
while-loop:
                w = cpumask_weight(curr);
                cnt = 0;

		while (cnt < w) {

> > +			cpumask_copy(cpus, curr);
> > +			for_each_cpu(cpu, cpus) {
> > +				irq_set_affinity_and_hint(irqs[i], topology_sibling_cpumask(cpu));
> > +				if (++i == nvec)
> > +					goto done;
> 
> Think what if you're passed with irq_setup(NULL, 0, 0).
> That's why I suggested to place this check at the beginning.
> 
> 
> > +				cpumask_andnot(cpus, cpus, topology_sibling_cpumask(cpu));
> > +				++cnt;
> > +			}
> > +		}
> > +		prev = next;
> > +	}

Don't hesitate to add even more vertical spacing. It's like: "take a
breath folks, this section is done". :)

> > +done:
> > +	rcu_read_unlock();
> > +	free_cpumask_var(curr);
> > +	free_cpumask_var(cpus);
> > +	return err;
> > +}
> > +
> >  static int mana_gd_setup_irqs(struct pci_dev *pdev)
> >  {
> > -	unsigned int max_queues_per_port = num_online_cpus();
> >  	struct gdma_context *gc = pci_get_drvdata(pdev);
> > +	unsigned int max_queues_per_port;
> >  	struct gdma_irq_context *gic;
> >  	unsigned int max_irqs, cpu;
> > -	int nvec, irq;
> > +	int start_irq_index = 1;
> > +	int nvec, *irqs, irq;
> >  	int err, i = 0, j;
> >  
> > +	cpus_read_lock();
> > +	max_queues_per_port = num_online_cpus();
> >  	if (max_queues_per_port > MANA_MAX_NUM_QUEUES)
> >  		max_queues_per_port = MANA_MAX_NUM_QUEUES;
> >  
> > @@ -1261,6 +1302,14 @@ static int mana_gd_setup_irqs(struct pci_dev *pdev)
> >  	nvec = pci_alloc_irq_vectors(pdev, 2, max_irqs, PCI_IRQ_MSIX);
> >  	if (nvec < 0)
> >  		return nvec;
> > +	if (nvec <= num_online_cpus())
> > +		start_irq_index = 0;
> > +
> > +	irqs = kmalloc_array((nvec - start_irq_index), sizeof(int), GFP_KERNEL);
> > +	if (!irqs) {
> > +		err = -ENOMEM;
> > +		goto free_irq_vector;
> > +	}
> >  
> >  	gc->irq_contexts = kcalloc(nvec, sizeof(struct gdma_irq_context),
> >  				   GFP_KERNEL);
> > @@ -1287,21 +1336,44 @@ static int mana_gd_setup_irqs(struct pci_dev *pdev)
> >  			goto free_irq;
> >  		}
> >  
> > -		err = request_irq(irq, mana_gd_intr, 0, gic->name, gic);
> > -		if (err)
> > -			goto free_irq;
> > -
> > -		cpu = cpumask_local_spread(i, gc->numa_node);
> > -		irq_set_affinity_and_hint(irq, cpumask_of(cpu));
> > +		if (!i) {
> > +			err = request_irq(irq, mana_gd_intr, 0, gic->name, gic);
> > +			if (err)
> > +				goto free_irq;
> > +
> > +			/* If number of IRQ is one extra than number of online CPUs,
> > +			 * then we need to assign IRQ0 (hwc irq) and IRQ1 to
> > +			 * same CPU.
> > +			 * Else we will use different CPUs for IRQ0 and IRQ1.
> > +			 * Also we are using cpumask_local_spread instead of
> > +			 * cpumask_first for the node, because the node can be
> > +			 * mem only.
> > +			 */
> > +			if (start_irq_index) {
> > +				cpu = cpumask_local_spread(i, gc->numa_node);
> 
> I already mentioned that: if i == 0, you don't need to spread, just
> pick 1st cpu from node.
> 
> > +				irq_set_affinity_and_hint(irq, cpumask_of(cpu));
> > +			} else {
> > +				irqs[start_irq_index] = irq;
> > +			}
> > +		} else {
> > +			irqs[i - start_irq_index] = irq;
> > +			err = request_irq(irqs[i - start_irq_index], mana_gd_intr, 0,
> > +					  gic->name, gic);
> > +			if (err)
> > +				goto free_irq;
> > +		}
> >  	}
> >  
> > +	err = irq_setup(irqs, (nvec - start_irq_index), gc->numa_node);
> > +	if (err)
> > +		goto free_irq;
> >  	err = mana_gd_alloc_res_map(nvec, &gc->msix_resource);
> >  	if (err)
> >  		goto free_irq;
> >  
> >  	gc->max_num_msix = nvec;
> >  	gc->num_msix_usable = nvec;
> > -
> > +	cpus_read_unlock();
> >  	return 0;
> >  
> >  free_irq:
> > @@ -1314,8 +1386,10 @@ static int mana_gd_setup_irqs(struct pci_dev *pdev)
> >  	}
> >  
> >  	kfree(gc->irq_contexts);
> > +	kfree(irqs);
> >  	gc->irq_contexts = NULL;
> >  free_irq_vector:
> > +	cpus_read_unlock();
> >  	pci_free_irq_vectors(pdev);
> >  	return err;
> >  }
> > -- 
> > 2.34.1