Re: [PATCH net-next,1/1] hv_netvsc: use per_cpu stats to calculate TX/RX data

[David Miller]

From: sixiao@xxxxxxxxxxxxx
Date: Tue, 12 May 2015 15:50:02 -0700

> From: Simon Xiao <sixiao@xxxxxxxxxxxxx>
> 
> Current code does not lock anything when calculating the TX and RX stats.
> As a result, the RX and TX data reported by ifconfig are not accuracy in a
> system with high network throughput and multiple CPUs (in my test,
> RX/TX = 83% between 2 HyperV VM nodes which have 8 vCPUs and 40G Ethernet).
> 
> This patch fixed the above issue by using per_cpu stats.
> netvsc_get_stats64() summarizes TX and RX data by iterating over all CPUs
> to get their respective stats.
> 
> Signed-off-by: Simon Xiao <sixiao@xxxxxxxxxxxxx>
> Reviewed-by: K. Y. Srinivasan <kys@xxxxxxxxxxxxx>
> Reviewed-by: Haiyang Zhang <haiyangz@xxxxxxxxxxxxx>
> ---
>  drivers/net/hyperv/hyperv_net.h |  9 +++++
>  drivers/net/hyperv/netvsc_drv.c | 80 ++++++++++++++++++++++++++++++++++++-----
>  2 files changed, 81 insertions(+), 8 deletions(-)
> 
> diff --git a/drivers/net/hyperv/hyperv_net.h b/drivers/net/hyperv/hyperv_net.h
> index 41071d3..5a92b36 100644
> --- a/drivers/net/hyperv/hyperv_net.h
> +++ b/drivers/net/hyperv/hyperv_net.h
> @@ -611,6 +611,12 @@ struct multi_send_data {
>  	u32 count; /* counter of batched packets */
>  };
>  
> +struct netvsc_stats {
> +	u64 packets;
> +	u64 bytes;
> +	struct u64_stats_sync s_sync;
> +};
> +
>  /* The context of the netvsc device  */
>  struct net_device_context {
>  	/* point back to our device context */
> @@ -618,6 +624,9 @@ struct net_device_context {
>  	struct delayed_work dwork;
>  	struct work_struct work;
>  	u32 msg_enable; /* debug level */
> +
> +	struct netvsc_stats __percpu *tx_stats;
> +	struct netvsc_stats __percpu *rx_stats;
>  };
>  
>  /* Per netvsc device */
> diff --git a/drivers/net/hyperv/netvsc_drv.c b/drivers/net/hyperv/netvsc_drv.c
> index 5993c7e..310b902 100644
> --- a/drivers/net/hyperv/netvsc_drv.c
> +++ b/drivers/net/hyperv/netvsc_drv.c
> @@ -391,7 +391,7 @@ static int netvsc_start_xmit(struct sk_buff *skb, struct net_device *net)
>  	u32 skb_length;
>  	u32 pkt_sz;
>  	struct hv_page_buffer page_buf[MAX_PAGE_BUFFER_COUNT];
> -
> +	struct netvsc_stats *tx_stats = this_cpu_ptr(net_device_ctx->tx_stats);
>  
>  	/* We will atmost need two pages to describe the rndis
>  	 * header. We can only transmit MAX_PAGE_BUFFER_COUNT number
> @@ -580,8 +580,10 @@ do_send:
>  
>  drop:
>  	if (ret == 0) {
> -		net->stats.tx_bytes += skb_length;
> -		net->stats.tx_packets++;
> +		u64_stats_update_begin(&tx_stats->s_sync);
> +		tx_stats->packets++;
> +		tx_stats->bytes += skb_length;
> +		u64_stats_update_end(&tx_stats->s_sync);
>  	} else {
>  		if (ret != -EAGAIN) {
>  			dev_kfree_skb_any(skb);
> @@ -644,13 +646,17 @@ int netvsc_recv_callback(struct hv_device *device_obj,
>  				struct ndis_tcp_ip_checksum_info *csum_info)
>  {
>  	struct net_device *net;
> +	struct net_device_context *net_device_ctx;
>  	struct sk_buff *skb;
> +	struct netvsc_stats *rx_stats;
>  
>  	net = ((struct netvsc_device *)hv_get_drvdata(device_obj))->ndev;
>  	if (!net || net->reg_state != NETREG_REGISTERED) {
>  		packet->status = NVSP_STAT_FAIL;
>  		return 0;
>  	}
> +	net_device_ctx = netdev_priv(net);
> +	rx_stats = this_cpu_ptr(net_device_ctx->rx_stats);
>  
>  	/* Allocate a skb - TODO direct I/O to pages? */
>  	skb = netdev_alloc_skb_ip_align(net, packet->total_data_buflen);
> @@ -686,8 +692,10 @@ int netvsc_recv_callback(struct hv_device *device_obj,
>  	skb_record_rx_queue(skb, packet->channel->
>  			    offermsg.offer.sub_channel_index);
>  
> -	net->stats.rx_packets++;
> -	net->stats.rx_bytes += packet->total_data_buflen;
> +	u64_stats_update_begin(&rx_stats->s_sync);
> +	rx_stats->packets++;
> +	rx_stats->bytes += packet->total_data_buflen;
> +	u64_stats_update_end(&rx_stats->s_sync);
>  
>  	/*
>  	 * Pass the skb back up. Network stack will deallocate the skb when it
> @@ -753,6 +761,46 @@ static int netvsc_change_mtu(struct net_device *ndev, int mtu)
>  	return 0;
>  }
>  
> +static struct rtnl_link_stats64 *netvsc_get_stats64(struct net_device *net,
> +						    struct rtnl_link_stats64 *t)
> +{
> +	struct net_device_context *ndev_ctx = netdev_priv(net);
> +	int cpu;
> +
> +	for_each_possible_cpu(cpu) {
> +		struct netvsc_stats *tx_stats = per_cpu_ptr(ndev_ctx->tx_stats,
> +							    cpu);
> +		struct netvsc_stats *rx_stats = per_cpu_ptr(ndev_ctx->rx_stats,
> +							    cpu);
> +		u64 tx_packets, tx_bytes, rx_packets, rx_bytes;
> +		unsigned int start;
> +
> +		do {
> +			start = u64_stats_fetch_begin_irq(&tx_stats->s_sync);
> +			tx_packets = tx_stats->packets;
> +			tx_bytes = tx_stats->bytes;
> +		} while (u64_stats_fetch_retry_irq(&tx_stats->s_sync, start));
> +
> +		do {
> +			start = u64_stats_fetch_begin_irq(&rx_stats->s_sync);
> +			rx_packets = rx_stats->packets;
> +			rx_bytes = rx_stats->bytes;
> +		} while (u64_stats_fetch_retry_irq(&rx_stats->s_sync, start));
> +
> +		t->tx_bytes	+= tx_bytes;
> +		t->tx_packets	+= tx_packets;
> +		t->rx_bytes	+= rx_bytes;
> +		t->rx_packets	+= rx_packets;
> +	}
> +
> +	t->tx_dropped	= net->stats.tx_dropped;
> +	t->tx_errors	= net->stats.tx_dropped;
> +
> +	t->rx_dropped	= net->stats.rx_dropped;
> +	t->rx_errors	= net->stats.rx_errors;
> +
> +	return t;
> +}
>  
>  static int netvsc_set_mac_addr(struct net_device *ndev, void *p)
>  {
> @@ -804,6 +852,7 @@ static const struct net_device_ops device_ops = {
>  	.ndo_validate_addr =		eth_validate_addr,
>  	.ndo_set_mac_address =		netvsc_set_mac_addr,
>  	.ndo_select_queue =		netvsc_select_queue,
> +	.ndo_get_stats64 =		netvsc_get_stats64,
>  #ifdef CONFIG_NET_POLL_CONTROLLER
>  	.ndo_poll_controller =		netvsc_poll_controller,
>  #endif
> @@ -855,6 +904,14 @@ static void netvsc_link_change(struct work_struct *w)
>  		netdev_notify_peers(net);
>  }
>  
> +static void netvsc_free_netdev(struct net_device *netdev)
> +{
> +	struct net_device_context *net_device_ctx = netdev_priv(netdev);
> +
> +	free_percpu(net_device_ctx->tx_stats);
> +	free_percpu(net_device_ctx->rx_stats);
> +	free_netdev(netdev);
> +}
>  
>  static int netvsc_probe(struct hv_device *dev,
>  			const struct hv_vmbus_device_id *dev_id)
> @@ -883,6 +940,13 @@ static int netvsc_probe(struct hv_device *dev,
>  		netdev_dbg(net, "netvsc msg_enable: %d\n",
>  			   net_device_ctx->msg_enable);
>  
> +	net_device_ctx->tx_stats = netdev_alloc_pcpu_stats(struct netvsc_stats);
> +	if (!net_device_ctx->tx_stats)
> +		return -ENOMEM;
> +	net_device_ctx->rx_stats = netdev_alloc_pcpu_stats(struct netvsc_stats);
> +	if (!net_device_ctx->rx_stats)
> +		return -ENOMEM;

Both of these return statements leak.

The first one leaks the net_device, the second one leaks the net_device
and the ->tx_stats memory.

You have to have cleanup paths here.
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