[PATCH net-next 2/3] net: Optimize xdp_do_flush() with bpf_net_context infos.

Sebastian Andrzej Siewior
2024-06-28T10:30:27Z

Every NIC driver utilizing XDP should invoke xdp_do_flush() after
processing all packages. With the introduction of the bpf_net_context
logic the flush lists (for dev, CPU-map and xsk) are lazy initialized
only if used. However xdp_do_flush() tries to flush all three of them so
all three lists are always initialized and the likely empty lists are
"iterated".
Without the usage of XDP but with CONFIG_DEBUG_NET the lists are also
initialized due to xdp_do_check_flushed().

Jakub suggest to utilize the hints in bpf_net_context and avoid invoking
the flush function. This will also avoiding initializing the lists which
are otherwise unused.

Introduce bpf_net_ctx_get_all_used_flush_lists() to return the
individual list if not-empty. Use the logic in xdp_do_flush() and
xdp_do_check_flushed(). Remove the not needed .*_check_flush().

Suggested-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
---
include/linux/bpf.h | 10 ++++------
include/linux/filter.h | 27 +++++++++++++++++++++++++++
include/net/xdp_sock.h | 14 ++------------
kernel/bpf/cpumap.c | 13 +------------
kernel/bpf/devmap.c | 13 +------------
net/core/filter.c | 33 +++++++++++++++++++++++++--------
net/xdp/xsk.c | 13 +------------
7 files changed, 61 insertions(+), 62 deletions(-)

diff --git a/include/linux/bpf.h b/include/linux/bpf.h
index a834f4b761bc5..f5c6bc9093a6b 100644
--- a/include/linux/bpf.h
+++ b/include/linux/bpf.h
@@ -2494,7 +2494,7 @@ struct sk_buff;
struct bpf_dtab_netdev;
struct bpf_cpu_map_entry;

-void __dev_flush(void);
+void __dev_flush(struct list_head *flush_list);
int dev_xdp_enqueue(struct net_device *dev, struct xdp_frame *xdpf,
struct net_device *dev_rx);
int dev_map_enqueue(struct bpf_dtab_netdev *dst, struct xdp_frame *xdpf,
@@ -2507,7 +2507,7 @@ int dev_map_redirect_multi(struct net_device *dev, struct sk_buff *skb,
struct bpf_prog *xdp_prog, struct bpf_map *map,
bool exclude_ingress);

-void __cpu_map_flush(void);
+void __cpu_map_flush(struct list_head *flush_list);
int cpu_map_enqueue(struct bpf_cpu_map_entry *rcpu, struct xdp_frame *xdpf,
struct net_device *dev_rx);
int cpu_map_generic_redirect(struct bpf_cpu_map_entry *rcpu,
@@ -2644,8 +2644,6 @@ void bpf_dynptr_init(struct bpf_dynptr_kern *ptr, void *data,
void bpf_dynptr_set_null(struct bpf_dynptr_kern *ptr);
void bpf_dynptr_set_rdonly(struct bpf_dynptr_kern *ptr);

-bool dev_check_flush(void);
-bool cpu_map_check_flush(void);
#else /* !CONFIG_BPF_SYSCALL */
static inline struct bpf_prog *bpf_prog_get(u32 ufd)
{
@@ -2738,7 +2736,7 @@ static inline struct bpf_token *bpf_token_get_from_fd(u32 ufd)
return ERR_PTR(-EOPNOTSUPP);
}

-static inline void __dev_flush(void)
+static inline void __dev_flush(struct list_head *flush_list)
{
}

@@ -2784,7 +2782,7 @@ int dev_map_redirect_multi(struct net_device *dev, struct sk_buff *skb,
return 0;
}

-static inline void __cpu_map_flush(void)
+static inline void __cpu_map_flush(struct list_head *flush_list)
{
}

diff --git a/include/linux/filter.h b/include/linux/filter.h
index c0349522de8fb..02ddcfdf94c46 100644
--- a/include/linux/filter.h
+++ b/include/linux/filter.h
@@ -829,6 +829,33 @@ static inline struct list_head *bpf_net_ctx_get_xskmap_flush_list(void)
return &bpf_net_ctx->xskmap_map_flush_list;
}

+static inline void bpf_net_ctx_get_all_used_flush_lists(struct list_head **lh_map,
+ struct list_head **lh_dev,
+ struct list_head **lh_xsk)
+{
+ struct bpf_net_context *bpf_net_ctx = bpf_net_ctx_get();
+ u32 kern_flags = bpf_net_ctx->ri.kern_flags;
+ struct list_head *lh;
+
+ *lh_map = *lh_dev = *lh_xsk = NULL;
+
+ if (!IS_ENABLED(CONFIG_BPF_SYSCALL))
+ return;
+
+ lh = &bpf_net_ctx->dev_map_flush_list;
+ if (kern_flags & BPF_RI_F_DEV_MAP_INIT && !list_empty(lh))
+ *lh_dev = lh;
+
+ lh = &bpf_net_ctx->cpu_map_flush_list;
+ if (kern_flags & BPF_RI_F_CPU_MAP_INIT && !list_empty(lh))
+ *lh_map = lh;
+
+ lh = &bpf_net_ctx->xskmap_map_flush_list;
+ if (IS_ENABLED(CONFIG_XDP_SOCKETS) &&
+ kern_flags & BPF_RI_F_XSK_MAP_INIT && !list_empty(lh))
+ *lh_xsk = lh;
+}
+
/* Compute the linear packet data range [data, data_end) which
* will be accessed by various program types (cls_bpf, act_bpf,
* lwt, ...). Subsystems allowing direct data access must (!)
diff --git a/include/net/xdp_sock.h b/include/net/xdp_sock.h
index 3d54de168a6d9..bfe625b55d55d 100644
--- a/include/net/xdp_sock.h
+++ b/include/net/xdp_sock.h
@@ -121,7 +121,7 @@ struct xsk_tx_metadata_ops {

int xsk_generic_rcv(struct xdp_sock *xs, struct xdp_buff *xdp);
int __xsk_map_redirect(struct xdp_sock *xs, struct xdp_buff *xdp);
-void __xsk_map_flush(void);
+void __xsk_map_flush(struct list_head *flush_list);

/**
* xsk_tx_metadata_to_compl - Save enough relevant metadata information
@@ -206,7 +206,7 @@ static inline int __xsk_map_redirect(struct xdp_sock *xs, struct xdp_buff *xdp)
return -EOPNOTSUPP;
}

-static inline void __xsk_map_flush(void)
+static inline void __xsk_map_flush(struct list_head *flush_list)
{
}

@@ -228,14 +228,4 @@ static inline void xsk_tx_metadata_complete(struct xsk_tx_metadata_compl *compl,
}

#endif /* CONFIG_XDP_SOCKETS */
-
-#if defined(CONFIG_XDP_SOCKETS) && defined(CONFIG_DEBUG_NET)
-bool xsk_map_check_flush(void);
-#else
-static inline bool xsk_map_check_flush(void)
-{
- return false;
-}
-#endif
-
#endif /* _LINUX_XDP_SOCK_H */
diff --git a/kernel/bpf/cpumap.c b/kernel/bpf/cpumap.c
index 068e994ed781a..4acf90cd79eb4 100644
--- a/kernel/bpf/cpumap.c
+++ b/kernel/bpf/cpumap.c
@@ -757,9 +757,8 @@ int cpu_map_generic_redirect(struct bpf_cpu_map_entry *rcpu,
return ret;
}

-void __cpu_map_flush(void)
+void __cpu_map_flush(struct list_head *flush_list)
{
- struct list_head *flush_list = bpf_net_ctx_get_cpu_map_flush_list();
struct xdp_bulk_queue *bq, *tmp;

list_for_each_entry_safe(bq, tmp, flush_list, flush_node) {
@@ -769,13 +768,3 @@ void __cpu_map_flush(void)
wake_up_process(bq->obj->kthread);
}
}
-
-#ifdef CONFIG_DEBUG_NET
-bool cpu_map_check_flush(void)
-{
- if (list_empty(bpf_net_ctx_get_cpu_map_flush_list()))
- return false;
- __cpu_map_flush();
- return true;
-}
-#endif
diff --git a/kernel/bpf/devmap.c b/kernel/bpf/devmap.c
index 317ac2d66ebd1..9ca47eaacdd5e 100644
--- a/kernel/bpf/devmap.c
+++ b/kernel/bpf/devmap.c
@@ -412,9 +412,8 @@ static void bq_xmit_all(struct xdp_dev_bulk_queue *bq, u32 flags)
* driver before returning from its napi->poll() routine. See the comment above
* xdp_do_flush() in filter.c.
*/
-void __dev_flush(void)
+void __dev_flush(struct list_head *flush_list)
{
- struct list_head *flush_list = bpf_net_ctx_get_dev_flush_list();
struct xdp_dev_bulk_queue *bq, *tmp;

list_for_each_entry_safe(bq, tmp, flush_list, flush_node) {
@@ -425,16 +424,6 @@ void __dev_flush(void)
}
}

-#ifdef CONFIG_DEBUG_NET
-bool dev_check_flush(void)
-{
- if (list_empty(bpf_net_ctx_get_dev_flush_list()))
- return false;
- __dev_flush();
- return true;
-}
-#endif
-
/* Elements are kept alive by RCU; either by rcu_read_lock() (from syscall) or
* by local_bh_disable() (from XDP calls inside NAPI). The
* rcu_read_lock_bh_held() below makes lockdep accept both.
diff --git a/net/core/filter.c b/net/core/filter.c
index eb1c4425c06f3..403d23faf22e1 100644
--- a/net/core/filter.c
+++ b/net/core/filter.c
@@ -4277,22 +4277,39 @@ static const struct bpf_func_proto bpf_xdp_adjust_meta_proto = {
*/
void xdp_do_flush(void)
{
- __dev_flush();
- __cpu_map_flush();
- __xsk_map_flush();
+ struct list_head *lh_map, *lh_dev, *lh_xsk;
+
+ bpf_net_ctx_get_all_used_flush_lists(&lh_map, &lh_dev, &lh_xsk);
+ if (lh_dev)
+ __dev_flush(lh_dev);
+ if (lh_map)
+ __cpu_map_flush(lh_map);
+ if (lh_xsk)
+ __xsk_map_flush(lh_xsk);
}
EXPORT_SYMBOL_GPL(xdp_do_flush);

#if defined(CONFIG_DEBUG_NET) && defined(CONFIG_BPF_SYSCALL)
void xdp_do_check_flushed(struct napi_struct *napi)
{
- bool ret;
+ struct list_head *lh_map, *lh_dev, *lh_xsk;
+ bool missed = false;

- ret = dev_check_flush();
- ret |= cpu_map_check_flush();
- ret |= xsk_map_check_flush();
+ bpf_net_ctx_get_all_used_flush_lists(&lh_map, &lh_dev, &lh_xsk);
+ if (lh_dev) {
+ __dev_flush(lh_dev);
+ missed = true;
+ }
+ if (lh_map) {
+ __cpu_map_flush(lh_map);
+ missed = true;
+ }
+ if (lh_xsk) {
+ __xsk_map_flush(lh_xsk);
+ missed = true;
+ }

- WARN_ONCE(ret, "Missing xdp_do_flush() invocation after NAPI by %ps\n",
+ WARN_ONCE(missed, "Missing xdp_do_flush() invocation after NAPI by %ps\n",
napi->poll);
}
#endif
diff --git a/net/xdp/xsk.c b/net/xdp/xsk.c
index ed062e0383896..de9c0322bc294 100644
--- a/net/xdp/xsk.c
+++ b/net/xdp/xsk.c
@@ -383,9 +383,8 @@ int __xsk_map_redirect(struct xdp_sock *xs, struct xdp_buff *xdp)
return 0;
}

-void __xsk_map_flush(void)
+void __xsk_map_flush(struct list_head *flush_list)
{
- struct list_head *flush_list = bpf_net_ctx_get_xskmap_flush_list();
struct xdp_sock *xs, *tmp;

list_for_each_entry_safe(xs, tmp, flush_list, flush_node) {
@@ -394,16 +393,6 @@ void __xsk_map_flush(void)
}
}

-#ifdef CONFIG_DEBUG_NET
-bool xsk_map_check_flush(void)
-{
- if (list_empty(bpf_net_ctx_get_xskmap_flush_list()))
- return false;
- __xsk_map_flush();
- return true;
-}
-#endif
-
void xsk_tx_completed(struct xsk_buff_pool *pool, u32 nb_entries)
{
xskq_prod_submit_n(pool->cq, nb_entries);
--
2.45.2