Subject: Re: [RFC 1/4] net: support per queue tx_usecs in sysfs

From: Florian Fainelli <[email-masked]>
Date: Tue, 01 Dec 2015 14:13:34 -0800

On 01/12/15 00:01, [email-masked] wrote:
> From: Kan Liang <[email-masked]>
> 
> Network devices usually have many queues. Each queue has its own
> tx_usecs options. Currently, we can only set all the queues with same
> value by ethtool. This patch expose the tx_usecs in sysfs. So the user
> can set/get per queue coalesce parameter tx_usecs by sysfs.

The new interface you propose makes things inconsistent, since we have
two separate configuration paths (sysfs and ethtool), and it would seem
better to have per-queue awareness in ethtool, since there is a whole
bunch of other parameters that could be configured on a per-queue basis.

Have you tried to extend existing ethtool interfaces to cover the need
for multiple queues?

> 
> Signed-off-by: Kan Liang <[email-masked]>
> ---
>  Documentation/networking/scaling.txt | 12 ++++++++++++
>  include/linux/netdevice.h            |  8 ++++++++
>  net/core/net-sysfs.c                 | 38 ++++++++++++++++++++++++++++++++++++
>  3 files changed, 58 insertions(+)
> 
> diff --git a/Documentation/networking/scaling.txt b/Documentation/networking/scaling.txt
> index 59f4db2..636192d 100644
> --- a/Documentation/networking/scaling.txt
> +++ b/Documentation/networking/scaling.txt
> @@ -431,6 +431,18 @@ a max-rate attribute is supported, by setting a Mbps value to
>  
>  A value of zero means disabled, and this is the default.
>  
> +Per Queue interrupt moderation:
> +=============================
> +
> +The interrupt moderation mechanism, which implemented by HW, employs
> +a series of timers to limit the number of interrupts it generates.
> +TX queue absolute delay timer can be set to a microseconds value with
> +
> +/sys/class/net/<dev>/queues/tx-<n>/tx_usecs
> +
> +For the device which doesn't support per queue interrupt moderation,
> +it shows "N/A".
> +
>  Further Information
>  ===================
>  RPS and RFS were introduced in kernel 2.6.35. XPS was incorporated into
> diff --git a/include/linux/netdevice.h b/include/linux/netdevice.h
> index 7d2d1d7..9db5c57 100644
> --- a/include/linux/netdevice.h
> +++ b/include/linux/netdevice.h
> @@ -1059,6 +1059,10 @@ typedef u16 (*select_queue_fallback_t)(struct net_device *dev,
>   *	This function is used to get egress tunnel information for given skb.
>   *	This is useful for retrieving outer tunnel header parameters while
>   *	sampling packet.
> + * void (*ndo_set_per_queue_tx_usecs)(struct net_device *dev,
> + * 				      int index, u32 val);
> + * void (*ndo_get_per_queue_tx_usecs)(struct net_device *dev, int index);
> + * 	This function is used to set/get per queue coalesce parameter tx_usecs.
>   *
>   */
>  struct net_device_ops {
> @@ -1236,6 +1240,10 @@ struct net_device_ops {
>  							 bool proto_down);
>  	int			(*ndo_fill_metadata_dst)(struct net_device *dev,
>  						       struct sk_buff *skb);
> +	void			(*ndo_set_per_queue_tx_usecs)(struct net_device *dev,
> +							      int index, u32 val);
> +	u32			(*ndo_get_per_queue_tx_usecs)(struct net_device *dev,
> +							      int index);
>  };
>  
>  /**
> diff --git a/net/core/net-sysfs.c b/net/core/net-sysfs.c
> index f88a62a..48016b8 100644
> --- a/net/core/net-sysfs.c
> +++ b/net/core/net-sysfs.c
> @@ -1239,12 +1239,50 @@ static struct netdev_queue_attribute xps_cpus_attribute =
>      __ATTR(xps_cpus, S_IRUGO | S_IWUSR, show_xps_map, store_xps_map);
>  #endif /* CONFIG_XPS */
>  
> +static ssize_t tx_usecs_show(struct netdev_queue *queue,
> +			     struct netdev_queue_attribute *attr,
> +			     char *buf)
> +{
> +	struct net_device *dev = queue->dev;
> +	int index = queue - dev->_tx;
> +	u32 val;
> +
> +	if (dev->netdev_ops->ndo_get_per_queue_tx_usecs) {
> +		val = dev->netdev_ops->ndo_get_per_queue_tx_usecs(dev, index);
> +		return sprintf(buf, "%u\n", val);
> +	}
> +
> +	return sprintf(buf, "N/A\n");
> +}
> +
> +static ssize_t tx_usecs_store(struct netdev_queue *queue,
> +			      struct netdev_queue_attribute *attr,
> +			      const char *buf, size_t len)
> +{
> +	struct net_device *dev = queue->dev;
> +	int index = queue - dev->_tx;
> +	u32 val, ret;
> +
> +	ret = kstrtouint(buf, 0, &val);
> +	if (ret < 0)
> +		return -EINVAL;
> +
> +	if (dev->netdev_ops->ndo_set_per_queue_tx_usecs)
> +		dev->netdev_ops->ndo_set_per_queue_tx_usecs(dev, index, val);
> +
> +	return len;
> +}
> +
> +static struct netdev_queue_attribute tx_usecs_attribute =
> +    __ATTR(tx_usecs, S_IRUGO | S_IWUSR, tx_usecs_show, tx_usecs_store);
> +
>  static struct attribute *netdev_queue_default_attrs[] = {
>  	&queue_trans_timeout.attr,
>  #ifdef CONFIG_XPS
>  	&xps_cpus_attribute.attr,
>  	&queue_tx_maxrate.attr,
>  #endif
> +	&tx_usecs_attribute.attr,
>  	NULL
>  };
>  
> 

-- 
Florian