netdev - Re: net/mlx4_en: Use affinity hint

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Date:	Thu, 2 Jan 2014 18:33:37 +0200
From:	Amir Vadai <amirv@...lanox.com>
To:	Ben Hutchings <bhutchings@...arflare.com>
Cc:	"David S. Miller" <davem@...emloft.net>, netdev@...r.kernel.org,
	Or Gerlitz <ogerlitz@...lanox.com>,
	Yuval Atias <yuvala@...lanox.com>
Subject: Re: net/mlx4_en: Use affinity hint

On 01/01/14 16:34 +0000, Ben Hutchings wrote:
> On Wed, 2014-01-01 at 15:05 +0200, Amir Vadai wrote:
> > From: Yuval Atias <yuvala@...lanox.com>
> > 
> > The “affinity hint” mechanism is used by the user space
> > daemon, irqbalancer, to indicate a preferred CPU mask for irqs.
> > Irqbalancer can use this hint to balance the irqs between the
> > cpus indicated by the mask.
> > 
> > We wish the HCA to preferentially map the IRQs it uses to numa cores
> > close to it.
> > To accomplish this, we use affinity hint: first we map IRQs to “close”
> > numa cores.
> > If these are exhausted, the remaining IRQs are mapped to “far” numa
> > cores.
> > 
> > Signed-off-by: Yuval Atias <yuvala@...lanox.com>
> [...]
> > --- a/drivers/net/ethernet/mellanox/mlx4/en_netdev.c
> > +++ b/drivers/net/ethernet/mellanox/mlx4/en_netdev.c
> > @@ -1532,6 +1532,45 @@ static void mlx4_en_linkstate(struct work_struct *work)
> >  	mutex_unlock(&mdev->state_lock);
> >  }
> >  
> > +static int mlx4_en_rings_affinity_hint(struct mlx4_en_priv *priv ,
> > +				      int *affinity_hint_mapping)
> > +{
> > +	int cpu;
> > +	int cores_arr_index = 0;
> > +	cpumask_t *numa_cores_mask;
> > +	cpumask_t *non_numa_cores_mask;
> 
> The types of these masks must be cpumask_var_t.
> 
Will be fixed in V1

> > +	if (!zalloc_cpumask_var(&non_numa_cores_mask, GFP_KERNEL)) {
> > +		en_err(priv, "Failed allocating cores mask\n");
> > +		return -EINVAL;
> > +	}
> > +	numa_cores_mask = (cpumask_t *)cpumask_of_node(
> > +					priv->mdev->dev->numa_node);
> > +	if (!cpumask_and(numa_cores_mask, cpu_online_mask, numa_cores_mask))
> > +		en_warn(priv, "Failed to find online cores for local numa\n");
> 
> This changes the CPU mask of your device's NUMA node.  Don't do that.
> You need to copy it to numa_cores_mask and then start changing it.
> 
Will change in V1

> [...]
> > @@ -1557,6 +1596,9 @@ int mlx4_en_start_port(struct net_device *dev)
> >  	memset(&priv->ethtool_rules[0], 0,
> >  	       sizeof(struct ethtool_flow_id) * MAX_NUM_OF_FS_RULES);
> >  
> > +	affinity_hint_mapping = kzalloc(num_online_cpus() * sizeof(int),
> > +					GFP_KERNEL);
> [...]
> 
> What makes you think that the online CPU IDs are all contiguous starting
> at 0?  The correct array size is nr_cpu_ids, if I remember correctly.
Changing the design to go over the cpumask using cpumask_next(),
instead of preparing this array. So, it will fix this comment too.

> 
> Ben.
> 
> -- 
> Ben Hutchings, Staff Engineer, Solarflare
> Not speaking for my employer; that's the marketing department's job.
> They asked us to note that Solarflare product names are trademarked.
> 
> --
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Thanks,
Amir
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