Re: [RFC net-next v3 5/9] net: napi: Add napi_config

[Stanislav Fomichev <stfomichev@gmail.com>]

On 09/12, Joe Damato wrote:
> Add a persistent NAPI config area for NAPI configuration to the core.
> Drivers opt-in to setting the storage for a NAPI by passing an index
> when calling netif_napi_add_storage.
> 
> napi_config is allocated in alloc_netdev_mqs, freed in free_netdev
> (after the NAPIs are deleted), and set to 0 when napi_enable is called.
> 
> Drivers which implement call netif_napi_add_storage will have persistent
> NAPI IDs.
> 
> Signed-off-by: Joe Damato <jdamato@fastly.com>
> ---
>  .../networking/net_cachelines/net_device.rst  |  1 +
>  include/linux/netdevice.h                     | 34 +++++++++
>  net/core/dev.c                                | 74 +++++++++++++++++--
>  net/core/dev.h                                | 12 +++
>  4 files changed, 113 insertions(+), 8 deletions(-)
> 
> diff --git a/Documentation/networking/net_cachelines/net_device.rst b/Documentation/networking/net_cachelines/net_device.rst
> index 3d02ae79c850..11d659051f5e 100644
> --- a/Documentation/networking/net_cachelines/net_device.rst
> +++ b/Documentation/networking/net_cachelines/net_device.rst
> @@ -183,3 +183,4 @@ struct hlist_head                   page_pools
>  struct dim_irq_moder*               irq_moder
>  unsigned_long                       gro_flush_timeout
>  u32                                 napi_defer_hard_irqs
> +struct napi_config*                 napi_config
> diff --git a/include/linux/netdevice.h b/include/linux/netdevice.h
> index 3e07ab8e0295..08afc96179f9 100644
> --- a/include/linux/netdevice.h
> +++ b/include/linux/netdevice.h
> @@ -342,6 +342,15 @@ struct gro_list {
>   */
>  #define GRO_HASH_BUCKETS	8
>  
> +/*
> + * Structure for per-NAPI storage
> + */
> +struct napi_config {
> +	u64 gro_flush_timeout;
> +	u32 defer_hard_irqs;
> +	unsigned int napi_id;
> +};
> +
>  /*
>   * Structure for NAPI scheduling similar to tasklet but with weighting
>   */
> @@ -379,6 +388,8 @@ struct napi_struct {
>  	int			irq;
>  	unsigned long		gro_flush_timeout;
>  	u32			defer_hard_irqs;
> +	int			index;
> +	struct napi_config	*config;
>  };
>  
>  enum {
> @@ -2011,6 +2022,9 @@ enum netdev_reg_state {
>   *	@dpll_pin: Pointer to the SyncE source pin of a DPLL subsystem,
>   *		   where the clock is recovered.
>   *
> + *	@napi_config: An array of napi_config structures containing per-NAPI
> + *		      settings.
> + *
>   *	FIXME: cleanup struct net_device such that network protocol info
>   *	moves out.
>   */
> @@ -2400,6 +2414,7 @@ struct net_device {
>  	struct dim_irq_moder	*irq_moder;
>  	unsigned long		gro_flush_timeout;
>  	u32			napi_defer_hard_irqs;
> +	struct napi_config	*napi_config;
>  
>  	u8			priv[] ____cacheline_aligned
>  				       __counted_by(priv_len);
> @@ -2650,6 +2665,23 @@ netif_napi_add_tx_weight(struct net_device *dev,
>  	netif_napi_add_weight(dev, napi, poll, weight);
>  }
>  
> +/**
> + * netif_napi_add_storage - initialize a NAPI context and set storage area
> + * @dev: network device
> + * @napi: NAPI context
> + * @poll: polling function
> + * @weight: the poll weight of this NAPI
> + * @index: the NAPI index
> + */
> +static inline void
> +netif_napi_add_storage(struct net_device *dev, struct napi_struct *napi,
> +		       int (*poll)(struct napi_struct *, int), int index)
> +{
> +	napi->index = index;
> +	napi->config = &dev->napi_config[index];
> +	netif_napi_add_weight(dev, napi, poll, NAPI_POLL_WEIGHT);
> +}
> +
>  /**
>   * netif_napi_add_tx() - initialize a NAPI context to be used for Tx only
>   * @dev:  network device
> @@ -2685,6 +2717,8 @@ void __netif_napi_del(struct napi_struct *napi);
>   */
>  static inline void netif_napi_del(struct napi_struct *napi)
>  {
> +	napi->config = NULL;
> +	napi->index = -1;
>  	__netif_napi_del(napi);
>  	synchronize_net();
>  }
> diff --git a/net/core/dev.c b/net/core/dev.c
> index f2fd503516de..ca2227d0b8ed 100644
> --- a/net/core/dev.c
> +++ b/net/core/dev.c
> @@ -6493,6 +6493,18 @@ EXPORT_SYMBOL(napi_busy_loop);
>  
>  #endif /* CONFIG_NET_RX_BUSY_POLL */
>  
> +static void napi_hash_add_with_id(struct napi_struct *napi, unsigned int napi_id)
> +{
> +	spin_lock(&napi_hash_lock);
> +
> +	napi->napi_id = napi_id;
> +
> +	hlist_add_head_rcu(&napi->napi_hash_node,
> +			   &napi_hash[napi->napi_id % HASH_SIZE(napi_hash)]);
> +
> +	spin_unlock(&napi_hash_lock);
> +}
> +
>  static void napi_hash_add(struct napi_struct *napi)
>  {
>  	if (test_bit(NAPI_STATE_NO_BUSY_POLL, &napi->state))
> @@ -6505,12 +6517,13 @@ static void napi_hash_add(struct napi_struct *napi)
>  		if (unlikely(++napi_gen_id < MIN_NAPI_ID))
>  			napi_gen_id = MIN_NAPI_ID;
>  	} while (napi_by_id(napi_gen_id));

[..]

> -	napi->napi_id = napi_gen_id;
> -
> -	hlist_add_head_rcu(&napi->napi_hash_node,
> -			   &napi_hash[napi->napi_id % HASH_SIZE(napi_hash)]);
>  
>  	spin_unlock(&napi_hash_lock);
> +
> +	napi_hash_add_with_id(napi, napi_gen_id);

nit: it is very unlikely that napi_gen_id is gonna wrap around after the
spin_unlock above, but maybe it's safer to have the following?

static void __napi_hash_add_with_id(struct napi_struct *napi, unsigned int napi_id)
{
	napi->napi_id = napi_id;
	hlist_add_head_rcu(&napi->napi_hash_node,
			   &napi_hash[napi->napi_id % HASH_SIZE(napi_hash)]);
}

static void napi_hash_add_with_id(struct napi_struct *napi, unsigned int napi_id)
{
	spin_lock(&napi_hash_lock);
	__napi_hash_add_with_id(...);
	spin_unlock(&napi_hash_lock);
}

And use __napi_hash_add_with_id here before spin_unlock?