Re: [PATCH net-next v4] net/core: Introduce netdev_core_stats_inc() for trace

From: Yajun Deng
Date: Tue Sep 19 2023 - 09:43:33 EST



On 2023/9/19 17:10, Paolo Abeni wrote:
On Mon, 2023-09-18 at 10:40 +0800, Yajun Deng wrote:
Although there is a kfree_skb_reason() helper function that can be used to
find the reason why this skb is dropped, but most callers didn't increase
one of rx_dropped, tx_dropped, rx_nohandler and rx_otherhost_dropped.

For the users, people are more concerned about why the dropped in ip
is increasing.

Introduce netdev_core_stats_inc() for trace. Also, move dev_core_stats()
and netdev_core_stats_alloc() to dev.c, as they are not called externally.

Signed-off-by: Yajun Deng <yajun.deng@xxxxxxxxx>
Suggested-by: Alexander Lobakin <aleksander.lobakin@xxxxxxxxx>
---
v4: Introduce netdev_core_stats_inc() instead of export dev_core_stats_*_inc()
v3: __cold should be added to the netdev_core_stats_alloc().
v2: use __cold instead of inline in dev_core_stats().
v1: https://lore.kernel.org/netdev/20230911082016.3694700-1-yajun.deng@xxxxxxxxx/
---
include/linux/netdevice.h | 21 ++++-----------------
net/core/dev.c | 26 ++++++++++++++++++++++++--
2 files changed, 28 insertions(+), 19 deletions(-)

diff --git a/include/linux/netdevice.h b/include/linux/netdevice.h
index 0896aaa91dd7..cddd4873b5b0 100644
--- a/include/linux/netdevice.h
+++ b/include/linux/netdevice.h
@@ -3980,32 +3980,19 @@ static __always_inline bool __is_skb_forwardable(const struct net_device *dev,
return false;
}
-struct net_device_core_stats __percpu *netdev_core_stats_alloc(struct net_device *dev);
-
-static inline struct net_device_core_stats __percpu *dev_core_stats(struct net_device *dev)
-{
- /* This READ_ONCE() pairs with the write in netdev_core_stats_alloc() */
- struct net_device_core_stats __percpu *p = READ_ONCE(dev->core_stats);
-
- if (likely(p))
- return p;
-
- return netdev_core_stats_alloc(dev);
-}
+void netdev_core_stats_inc(struct net_device *dev, u32 offset);
#define DEV_CORE_STATS_INC(FIELD) \
static inline void dev_core_stats_##FIELD##_inc(struct net_device *dev) \
{ \
- struct net_device_core_stats __percpu *p; \
- \
- p = dev_core_stats(dev); \
- if (p) \
- this_cpu_inc(p->FIELD); \
+ netdev_core_stats_inc(dev, \
+ offsetof(struct net_device_core_stats, FIELD)); \
}
DEV_CORE_STATS_INC(rx_dropped)
DEV_CORE_STATS_INC(tx_dropped)
DEV_CORE_STATS_INC(rx_nohandler)
DEV_CORE_STATS_INC(rx_otherhost_dropped)
+#undef DEV_CORE_STATS_INC
static __always_inline int ____dev_forward_skb(struct net_device *dev,
struct sk_buff *skb,
diff --git a/net/core/dev.c b/net/core/dev.c
index ccff2b6ef958..f4cccdf05450 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -10475,7 +10475,8 @@ void netdev_stats_to_stats64(struct rtnl_link_stats64 *stats64,
}
EXPORT_SYMBOL(netdev_stats_to_stats64);
-struct net_device_core_stats __percpu *netdev_core_stats_alloc(struct net_device *dev)
+static __cold struct net_device_core_stats __percpu *netdev_core_stats_alloc(
+ struct net_device *dev)
{
struct net_device_core_stats __percpu *p;
@@ -10488,7 +10489,28 @@ struct net_device_core_stats __percpu *netdev_core_stats_alloc(struct net_device
/* This READ_ONCE() pairs with the cmpxchg() above */
return READ_ONCE(dev->core_stats);
}
-EXPORT_SYMBOL(netdev_core_stats_alloc);
+
+static inline struct net_device_core_stats __percpu *netdev_core_stats(
+ struct net_device *dev)
+{
+ /* This READ_ONCE() pairs with the write in netdev_core_stats_alloc() */
+ struct net_device_core_stats __percpu *p = READ_ONCE(dev->core_stats);
+
+ if (likely(p))
+ return p;
+
+ return netdev_core_stats_alloc(dev);
+}
+
+void netdev_core_stats_inc(struct net_device *dev, u32 offset)
+{
+ struct net_device_core_stats __percpu *p;
+
+ p = netdev_core_stats(dev);
+ if (p)
+ this_cpu_inc(*(unsigned long *)((void *)p + offset));
The above is causing a lot of compile warning, as it's discarding the
(required) __percpu annotation.

You need to first access the per cpu pointer and then reach for the
relevant offset.
Indeed, thanks.

Cheers,

Paolo