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

[Yury Norov <yury.norov@gmail.com>]

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@gmali.com>
> Signed-off-by: Souradeep Chakrabarti <schakrabarti@linux.microsoft.com>
> ---

[...]

>  .../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)) {
> +		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; ) {
> +			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;
> +	}
> +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