netdev - Re: [PATCH net-next v6 1/5] net: move ARFS rmap management to core

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Message-ID: <414c773d-5b7b-44b8-82a7-da49168ee791@intel.com>
Date: Thu, 23 Jan 2025 13:13:10 -0700
From: Ahmed Zaki <ahmed.zaki@...el.com>
To: Joe Damato <jdamato@...tly.com>, <netdev@...r.kernel.org>,
	<intel-wired-lan@...ts.osuosl.org>, <andrew+netdev@...n.ch>,
	<edumazet@...gle.com>, <kuba@...nel.org>, <horms@...nel.org>,
	<pabeni@...hat.com>, <davem@...emloft.net>, <michael.chan@...adcom.com>,
	<tariqt@...dia.com>, <anthony.l.nguyen@...el.com>,
	<przemyslaw.kitszel@...el.com>, <shayd@...dia.com>,
	<akpm@...ux-foundation.org>, <shayagr@...zon.com>,
	<kalesh-anakkur.purayil@...adcom.com>, David Arinzon <darinzon@...zon.com>
Subject: Re: [PATCH net-next v6 1/5] net: move ARFS rmap management to core



On 2025-01-23 12:28 p.m., Joe Damato wrote:
> On Fri, Jan 17, 2025 at 05:33:31PM -0700, Ahmed Zaki wrote:
>> Add a new netdev flag "rx_cpu_rmap_auto". Drivers supporting ARFS should
>> set the flag via netif_enable_cpu_rmap() and core will allocate and manage
>> the ARFS rmap. Freeing the rmap is also done by core when the netdev is
>> freed.
>>
>> For better IRQ affinity management, move the IRQ rmap notifier inside the
>> napi_struct. Consequently, add new notify.notify and notify.release
>> functions: netif_irq_cpu_rmap_notify() and netif_napi_affinity_release().
>>
>> Acked-by: David Arinzon <darinzon@...zon.com>
>> Signed-off-by: Ahmed Zaki <ahmed.zaki@...el.com>
> 
> [...]
> 
>> diff --git a/net/core/dev.c b/net/core/dev.c
>> index fe5f5855593d..dbb63005bc2b 100644
>> --- a/net/core/dev.c
>> +++ b/net/core/dev.c
>> @@ -6862,6 +6862,141 @@ void netif_queue_set_napi(struct net_device *dev, unsigned int queue_index,
>>   }
>>   EXPORT_SYMBOL(netif_queue_set_napi);
>>   
>> +#ifdef CONFIG_RFS_ACCEL
>> +static void
>> +netif_irq_cpu_rmap_notify(struct irq_affinity_notify *notify,
>> +			  const cpumask_t *mask)
>> +{
>> +	struct napi_struct *napi =
>> +		container_of(notify, struct napi_struct, notify);
>> +	struct cpu_rmap *rmap = napi->dev->rx_cpu_rmap;
>> +	int err;
> 
> I wonder if this generates a warning with some compilers? err is
> defined not used if !napi->dev->rx_cpu_rmap_auto ? Not sure.
> 
>> +	if (napi->dev->rx_cpu_rmap_auto) {
>> +		err = cpu_rmap_update(rmap, napi->napi_rmap_idx, mask);
>> +		if (err)
>> +			pr_warn("%s: RMAP update failed (%d)\n",
>> +				__func__, err);
>> +	}
>> +}
>> +
>> +static void netif_napi_affinity_release(struct kref *ref)
>> +{
>> +	struct napi_struct *napi =
>> +		container_of(ref, struct napi_struct, notify.kref);
>> +	struct cpu_rmap *rmap = napi->dev->rx_cpu_rmap;
>> +
>> +	if (!napi->dev->rx_cpu_rmap_auto)
>> +		return;
>> +	rmap->obj[napi->napi_rmap_idx] = NULL;
>> +	napi->napi_rmap_idx = -1;
>> +	cpu_rmap_put(rmap);
>> +}
>> +
>> +static int napi_irq_cpu_rmap_add(struct napi_struct *napi, int irq)
>> +{
>> +	struct cpu_rmap *rmap = napi->dev->rx_cpu_rmap;
>> +	int rc;
>> +
>> +	if (!rmap)
>> +		return -EINVAL;
>> +
>> +	napi->notify.notify = netif_irq_cpu_rmap_notify;
>> +	napi->notify.release = netif_napi_affinity_release;
> 
> Maybe the callbacks should only be set at the end after everything
> else is successful, just before the return 0 ?
> 

I believe this is needed before irq_set_affinity_notifier(), OW we could 
have some racing. I can move it there if you like.

>> +	cpu_rmap_get(rmap);
>> +	rc = cpu_rmap_add(rmap, napi);
>> +	if (rc < 0)
>> +		goto err_add;
>> +
>> +	napi->napi_rmap_idx = rc;
>> +	rc = irq_set_affinity_notifier(irq, &napi->notify);
>> +	if (rc)
>> +		goto err_set;
>> +
>> +	return 0;
>> +
>> +err_set:
>> +	rmap->obj[napi->napi_rmap_idx] = NULL;
>> +	napi->napi_rmap_idx = -1;
>> +err_add:
>> +	cpu_rmap_put(rmap);
>> +	return rc;
>> +}
> 
> [...]
> 
>> +void netif_napi_set_irq_locked(struct napi_struct *napi, int irq)
>> +{
>> +	int rc;
>> +
>> +	if (!napi->dev->rx_cpu_rmap_auto)
>> +		goto out;
> 
> Maybe the above if statement could be extended to be something like:
> 
> if (!napi->dev->rx_cpu_rmap_auto || napi->irq < 0)
>    goto out;
> 
> then you can omit the irq > 0 checks in the code below, potentially?

I am afraid I don't get this, the checks below one is for the new irq 
(could be valid or -1) and one for the existing (nap->irq).

> 
>> +	/* Remove existing rmap entries */
>> +	if (napi->irq != irq && napi->irq > 0)
>> +		irq_set_affinity_notifier(napi->irq, NULL);
>> +
>> +	if (irq > 0) {
>> +		rc = napi_irq_cpu_rmap_add(napi, irq);
>> +		if (rc) {
>> +			netdev_warn(napi->dev, "Unable to update ARFS map (%d)\n",
>> +				    rc);
>> +			netif_disable_cpu_rmap(napi->dev);
>> +		}
>> +	}
>> +
>> +out:
>> +	napi->irq = irq;
>> +}
>> +EXPORT_SYMBOL(netif_napi_set_irq_locked);
>> +

Thanks.