[PATCH net-next v3 0/4] netdevsim: implement RX statistics using NETDEV_PCPU_STAT_DSTATS

[PATCH net-next v3 0/4] netdevsim: implement RX statistics using NETDEV_PCPU_STAT_DSTATS

[Breno Leitao]

The netdevsim driver previously lacked RX statistics support, which
prevented its use with the GenerateTraffic() test framework, as this
framework verifies traffic flow by checking RX byte counts.

This patch migrates netdevsim from its custom statistics collection to
the NETDEV_PCPU_STAT_DSTATS framework, as suggested by Jakub. This
change not only standardizes the statistics handling but also adds the
necessary RX statistics support required by the test framework.

Signed-off-by: Breno Leitao <leitao@debian.org>
---
Changes in v3:
- Rely on netdev from caller instead of napi->dev in nsim_queue_free().
- Link to v2: https://lore.kernel.org/r/20250613-netdevsim_stat-v2-0-98fa38836c48@debian.org

Changes in v2:
- Changed the RX collection place from nsim_napi_rx() to nsim_rcv (Joe
  Damato)
- Collect RX dropped packets statistic in nsim_queue_free() (Jakub)
- Added a helper in dstat to add values to RX dropped packets
- Link to v1: https://lore.kernel.org/r/20250611-netdevsim_stat-v1-0-c11b657d96bf@debian.org

---
Breno Leitao (4):
      netdevsim: migrate to dstats stats collection
      netdevsim: collect statistics at RX side
      net: add dev_dstats_rx_dropped_add() helper
      netdevsim: account dropped packet length in stats on queue free

 drivers/net/netdevsim/netdev.c    | 54 +++++++++++++++------------------------
 drivers/net/netdevsim/netdevsim.h |  5 ----
 include/linux/netdevice.h         | 10 ++++++++
 3 files changed, 31 insertions(+), 38 deletions(-)
---
base-commit: 3b5b1c428260152e47c9584bc176f358b87ca82d
change-id: 20250610-netdevsim_stat-95995921e03e

Best regards,
-- 
Breno Leitao <leitao@debian.org>

[PATCH net-next v3 1/4] netdevsim: migrate to dstats stats collection

[Breno Leitao]

Replace custom statistics tracking with the kernel's dstats infrastructure
to simplify code and improve consistency with other network drivers.

This change:
- Sets dev->pcpu_stat_type = NETDEV_PCPU_STAT_DSTATS for automatic
  automatic allocation and deallocation.
- Removes manual stats fields and their update
- Replaces custom nsim_get_stats64() with dev_get_stats()
- Uses dev_dstats_tx_add() and dev_dstats_tx_dropped() helpers
- Eliminates the need for manual synchronization primitives

The dstats framework provides the same functionality with less code.

Suggested-by: Jakub Kicinski <kuba@kernel.org>
Reviewed-by: Joe Damato <joe@dama.to>
Signed-off-by: Breno Leitao <leitao@debian.org>
---
 drivers/net/netdevsim/netdev.c    | 33 ++++++---------------------------
 drivers/net/netdevsim/netdevsim.h |  5 -----
 2 files changed, 6 insertions(+), 32 deletions(-)

diff --git a/drivers/net/netdevsim/netdev.c b/drivers/net/netdevsim/netdev.c
index fa5fbd97ad69e..5010d8eefc854 100644
--- a/drivers/net/netdevsim/netdev.c
+++ b/drivers/net/netdevsim/netdev.c
@@ -93,19 +93,14 @@ static netdev_tx_t nsim_start_xmit(struct sk_buff *skb, struct net_device *dev)
 		hrtimer_start(&rq->napi_timer, us_to_ktime(5), HRTIMER_MODE_REL);
 
 	rcu_read_unlock();
-	u64_stats_update_begin(&ns->syncp);
-	ns->tx_packets++;
-	ns->tx_bytes += len;
-	u64_stats_update_end(&ns->syncp);
+	dev_dstats_tx_add(dev, skb->len);
 	return NETDEV_TX_OK;
 
 out_drop_free:
 	dev_kfree_skb(skb);
 out_drop_cnt:
 	rcu_read_unlock();
-	u64_stats_update_begin(&ns->syncp);
-	ns->tx_dropped++;
-	u64_stats_update_end(&ns->syncp);
+	dev_dstats_tx_dropped(dev);
 	return NETDEV_TX_OK;
 }
 
@@ -126,20 +121,6 @@ static int nsim_change_mtu(struct net_device *dev, int new_mtu)
 	return 0;
 }
 
-static void
-nsim_get_stats64(struct net_device *dev, struct rtnl_link_stats64 *stats)
-{
-	struct netdevsim *ns = netdev_priv(dev);
-	unsigned int start;
-
-	do {
-		start = u64_stats_fetch_begin(&ns->syncp);
-		stats->tx_bytes = ns->tx_bytes;
-		stats->tx_packets = ns->tx_packets;
-		stats->tx_dropped = ns->tx_dropped;
-	} while (u64_stats_fetch_retry(&ns->syncp, start));
-}
-
 static int
 nsim_setup_tc_block_cb(enum tc_setup_type type, void *type_data, void *cb_priv)
 {
@@ -556,7 +537,6 @@ static const struct net_device_ops nsim_netdev_ops = {
 	.ndo_set_mac_address	= eth_mac_addr,
 	.ndo_validate_addr	= eth_validate_addr,
 	.ndo_change_mtu		= nsim_change_mtu,
-	.ndo_get_stats64	= nsim_get_stats64,
 	.ndo_set_vf_mac		= nsim_set_vf_mac,
 	.ndo_set_vf_vlan	= nsim_set_vf_vlan,
 	.ndo_set_vf_rate	= nsim_set_vf_rate,
@@ -580,7 +560,6 @@ static const struct net_device_ops nsim_vf_netdev_ops = {
 	.ndo_set_mac_address	= eth_mac_addr,
 	.ndo_validate_addr	= eth_validate_addr,
 	.ndo_change_mtu		= nsim_change_mtu,
-	.ndo_get_stats64	= nsim_get_stats64,
 	.ndo_setup_tc		= nsim_setup_tc,
 	.ndo_set_features	= nsim_set_features,
 };
@@ -594,7 +573,7 @@ static void nsim_get_queue_stats_rx(struct net_device *dev, int idx,
 	struct rtnl_link_stats64 rtstats = {};
 
 	if (!idx)
-		nsim_get_stats64(dev, &rtstats);
+		dev_get_stats(dev, &rtstats);
 
 	stats->packets = rtstats.rx_packets - !!rtstats.rx_packets;
 	stats->bytes = rtstats.rx_bytes;
@@ -606,7 +585,7 @@ static void nsim_get_queue_stats_tx(struct net_device *dev, int idx,
 	struct rtnl_link_stats64 rtstats = {};
 
 	if (!idx)
-		nsim_get_stats64(dev, &rtstats);
+		dev_get_stats(dev, &rtstats);
 
 	stats->packets = rtstats.tx_packets - !!rtstats.tx_packets;
 	stats->bytes = rtstats.tx_bytes;
@@ -618,7 +597,7 @@ static void nsim_get_base_stats(struct net_device *dev,
 {
 	struct rtnl_link_stats64 rtstats = {};
 
-	nsim_get_stats64(dev, &rtstats);
+	dev_get_stats(dev, &rtstats);
 
 	rx->packets = !!rtstats.rx_packets;
 	rx->bytes = 0;
@@ -890,6 +869,7 @@ static void nsim_setup(struct net_device *dev)
 			    NETIF_F_HW_CSUM |
 			    NETIF_F_LRO |
 			    NETIF_F_TSO;
+	dev->pcpu_stat_type = NETDEV_PCPU_STAT_DSTATS;
 	dev->max_mtu = ETH_MAX_MTU;
 	dev->xdp_features = NETDEV_XDP_ACT_HW_OFFLOAD;
 }
@@ -1022,7 +1002,6 @@ nsim_create(struct nsim_dev *nsim_dev, struct nsim_dev_port *nsim_dev_port)
 	dev_net_set(dev, nsim_dev_net(nsim_dev));
 	ns = netdev_priv(dev);
 	ns->netdev = dev;
-	u64_stats_init(&ns->syncp);
 	ns->nsim_dev = nsim_dev;
 	ns->nsim_dev_port = nsim_dev_port;
 	ns->nsim_bus_dev = nsim_dev->nsim_bus_dev;
diff --git a/drivers/net/netdevsim/netdevsim.h b/drivers/net/netdevsim/netdevsim.h
index d04401f0bdf79..343b8f19dbed6 100644
--- a/drivers/net/netdevsim/netdevsim.h
+++ b/drivers/net/netdevsim/netdevsim.h
@@ -108,11 +108,6 @@ struct netdevsim {
 
 	int rq_reset_mode;
 
-	u64 tx_packets;
-	u64 tx_bytes;
-	u64 tx_dropped;
-	struct u64_stats_sync syncp;
-
 	struct nsim_bus_dev *nsim_bus_dev;
 
 	struct bpf_prog	*bpf_offloaded;

-- 
2.47.1

[PATCH net-next v3 2/4] netdevsim: collect statistics at RX side

[Breno Leitao]

When the RX side of netdevsim was added, the RX statistics were missing,
making the driver unusable for GenerateTraffic() test framework.

This patch adds proper statistics tracking on RX side, complementing the
TX path.

Signed-off-by: Breno Leitao <leitao@debian.org>
---
 drivers/net/netdevsim/netdev.c | 12 ++++++++++--
 1 file changed, 10 insertions(+), 2 deletions(-)

diff --git a/drivers/net/netdevsim/netdev.c b/drivers/net/netdevsim/netdev.c
index 5010d8eefc854..de309ff69e43e 100644
--- a/drivers/net/netdevsim/netdev.c
+++ b/drivers/net/netdevsim/netdev.c
@@ -331,16 +331,24 @@ static int nsim_get_iflink(const struct net_device *dev)
 
 static int nsim_rcv(struct nsim_rq *rq, int budget)
 {
+	struct net_device *dev = rq->napi.dev;
 	struct sk_buff *skb;
-	int i;
+	unsigned int skblen;
+	int i, ret;
 
 	for (i = 0; i < budget; i++) {
 		if (skb_queue_empty(&rq->skb_queue))
 			break;
 
 		skb = skb_dequeue(&rq->skb_queue);
+		/* skb might be discard at netif_receive_skb, save the len */
+		skblen =  skb->len;
 		skb_mark_napi_id(skb, &rq->napi);
-		netif_receive_skb(skb);
+		ret = netif_receive_skb(skb);
+		if (ret == NET_RX_SUCCESS)
+			dev_dstats_rx_add(dev, skblen);
+		else
+			dev_dstats_rx_dropped(dev);
 	}
 
 	return i;

-- 
2.47.1

[PATCH net-next v3 3/4] net: add dev_dstats_rx_dropped_add() helper

[Breno Leitao]

Introduce the dev_dstats_rx_dropped_add() helper to allow incrementing
the rx_drops per-CPU statistic by an arbitrary value, rather than just
one. This is useful for drivers or code paths that need to account for
multiple dropped packets at once, such as when dropping entire queues.

Signed-off-by: Breno Leitao <leitao@debian.org>
---
 include/linux/netdevice.h | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/include/linux/netdevice.h b/include/linux/netdevice.h
index 9cbc4e54b7e4a..03c26bb0fbbef 100644
--- a/include/linux/netdevice.h
+++ b/include/linux/netdevice.h
@@ -3016,6 +3016,16 @@ static inline void dev_dstats_rx_dropped(struct net_device *dev)
 	u64_stats_update_end(&dstats->syncp);
 }
 
+static inline void dev_dstats_rx_dropped_add(struct net_device *dev,
+					     unsigned int packets)
+{
+	struct pcpu_dstats *dstats = this_cpu_ptr(dev->dstats);
+
+	u64_stats_update_begin(&dstats->syncp);
+	u64_stats_add(&dstats->rx_drops, packets);
+	u64_stats_update_end(&dstats->syncp);
+}
+
 static inline void dev_dstats_tx_add(struct net_device *dev,
 				     unsigned int len)
 {

-- 
2.47.1

[PATCH net-next v3 4/4] netdevsim: account dropped packet length in stats on queue free

[Breno Leitao]

Add a call to dev_dstats_rx_dropped_add() in nsim_queue_free() to
account for the number of packets dropped when purging the skb queue.

This improves the accuracy of RX drop statistics reported by
netdevsim.

Suggested-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Breno Leitao <leitao@debian.org>
---
 drivers/net/netdevsim/netdev.c | 9 +++++----
 1 file changed, 5 insertions(+), 4 deletions(-)

diff --git a/drivers/net/netdevsim/netdev.c b/drivers/net/netdevsim/netdev.c
index de309ff69e43e..5d0b801e81129 100644
--- a/drivers/net/netdevsim/netdev.c
+++ b/drivers/net/netdevsim/netdev.c
@@ -632,9 +632,10 @@ static struct nsim_rq *nsim_queue_alloc(void)
 	return rq;
 }
 
-static void nsim_queue_free(struct nsim_rq *rq)
+static void nsim_queue_free(struct net_device *dev, struct nsim_rq *rq)
 {
 	hrtimer_cancel(&rq->napi_timer);
+	dev_dstats_rx_dropped_add(dev, rq->skb_queue.qlen);
 	skb_queue_purge_reason(&rq->skb_queue, SKB_DROP_REASON_QUEUE_PURGE);
 	kfree(rq);
 }
@@ -681,7 +682,7 @@ nsim_queue_mem_alloc(struct net_device *dev, void *per_queue_mem, int idx)
 	return 0;
 
 err_free:
-	nsim_queue_free(qmem->rq);
+	nsim_queue_free(dev, qmem->rq);
 	return err;
 }
 
@@ -695,7 +696,7 @@ static void nsim_queue_mem_free(struct net_device *dev, void *per_queue_mem)
 		if (!ns->rq_reset_mode)
 			netif_napi_del_locked(&qmem->rq->napi);
 		page_pool_destroy(qmem->rq->page_pool);
-		nsim_queue_free(qmem->rq);
+		nsim_queue_free(dev, qmem->rq);
 	}
 }
 
@@ -913,7 +914,7 @@ static void nsim_queue_uninit(struct netdevsim *ns)
 	int i;
 
 	for (i = 0; i < dev->num_rx_queues; i++)
-		nsim_queue_free(ns->rq[i]);
+		nsim_queue_free(dev, ns->rq[i]);
 
 	kfree(ns->rq);
 	ns->rq = NULL;

-- 
2.47.1

Re: [PATCH net-next v3 4/4] netdevsim: account dropped packet length in stats on queue free

[Jakub Kicinski]

On Tue, 17 Jun 2025 01:19:00 -0700 Breno Leitao wrote:
> -static void nsim_queue_free(struct nsim_rq *rq)
> +static void nsim_queue_free(struct net_device *dev, struct nsim_rq *rq)
>  {
>  	hrtimer_cancel(&rq->napi_timer);
> +	dev_dstats_rx_dropped_add(dev, rq->skb_queue.qlen);

here we are in process context and debug checks complain about the use
of this_cpu_ptr(). Let's wrap this in local_bh_disable() / enable() ?

>  	skb_queue_purge_reason(&rq->skb_queue, SKB_DROP_REASON_QUEUE_PURGE);
>  	kfree(rq);
>  }
-- 
pw-bot: cr

Re: [PATCH net-next v3 4/4] netdevsim: account dropped packet length in stats on queue free

[Breno Leitao]

On Tue, Jun 17, 2025 at 05:59:34AM -0700, Jakub Kicinski wrote:
> On Tue, 17 Jun 2025 01:19:00 -0700 Breno Leitao wrote:
> > -static void nsim_queue_free(struct nsim_rq *rq)
> > +static void nsim_queue_free(struct net_device *dev, struct nsim_rq *rq)
> >  {
> >  	hrtimer_cancel(&rq->napi_timer);
> > +	dev_dstats_rx_dropped_add(dev, rq->skb_queue.qlen);
> 
> here we are in process context and debug checks complain about the use
> of this_cpu_ptr(). Let's wrap this in local_bh_disable() / enable() ?

Thanks. I was able to reproduce it. Your suggestion avoids the complain.
I suppose we should just wrap dev_dstats_rx_dropped_add(), right?

	diff --git a/drivers/net/netdevsim/netdev.c b/drivers/net/netdevsim/netdev.c
	index 5d0b801e81129..07171cf8b07ee 100644
	--- a/drivers/net/netdevsim/netdev.c
	+++ b/drivers/net/netdevsim/netdev.c
	@@ -635,7 +635,9 @@ static struct nsim_rq *nsim_queue_alloc(void)
	static void nsim_queue_free(struct net_device *dev, struct nsim_rq *rq)
	{
		hrtimer_cancel(&rq->napi_timer);
	+	local_bh_disable();
		dev_dstats_rx_dropped_add(dev, rq->skb_queue.qlen);
	+	local_bh_enable();
		skb_queue_purge_reason(&rq->skb_queue, SKB_DROP_REASON_QUEUE_PURGE);
		kfree(rq);
	}

Re: [PATCH net-next v3 4/4] netdevsim: account dropped packet length in stats on queue free

[Jakub Kicinski]

On Tue, 17 Jun 2025 06:24:23 -0700 Breno Leitao wrote:
> > here we are in process context and debug checks complain about the use
> > of this_cpu_ptr(). Let's wrap this in local_bh_disable() / enable() ?  
> 
> Thanks. I was able to reproduce it. Your suggestion avoids the complain.
> I suppose we should just wrap dev_dstats_rx_dropped_add(), right?

I think so. I hope that makes the preempt checker happy.
The reason for bh_disable rather than preempt_disable() is that we 
should only update the stats from one context, the NAPI poll context.
So we also need to prevent races with another NAPI running on the same
core while we free an old queue.

Re: [PATCH net-next v3 2/4] netdevsim: collect statistics at RX side

[Joe Damato]

On Tue, Jun 17, 2025 at 01:18:58AM -0700, Breno Leitao wrote:
> When the RX side of netdevsim was added, the RX statistics were missing,
> making the driver unusable for GenerateTraffic() test framework.
> 
> This patch adds proper statistics tracking on RX side, complementing the
> TX path.
> 
> Signed-off-by: Breno Leitao <leitao@debian.org>
> ---
>  drivers/net/netdevsim/netdev.c | 12 ++++++++++--
>  1 file changed, 10 insertions(+), 2 deletions(-)
> 

Thanks for moving the RX accounting around.

Reviewed-by: Joe Damato <joe@dama.to>

Re: [PATCH net-next v3 3/4] net: add dev_dstats_rx_dropped_add() helper

[Joe Damato]

On Tue, Jun 17, 2025 at 01:18:59AM -0700, Breno Leitao wrote:
> Introduce the dev_dstats_rx_dropped_add() helper to allow incrementing
> the rx_drops per-CPU statistic by an arbitrary value, rather than just
> one. This is useful for drivers or code paths that need to account for
> multiple dropped packets at once, such as when dropping entire queues.
> 
> Signed-off-by: Breno Leitao <leitao@debian.org>
> ---
>  include/linux/netdevice.h | 10 ++++++++++
>  1 file changed, 10 insertions(+)
>

Reviewed-by: Joe Damato <joe@dama.to>