Re: [PATCH net-next 6/6] net: hns3: use napi_consume_skb() when cleaning tx desc

On 2020/9/16 16:38, Eric Dumazet wrote:

On Wed, Sep 16, 2020 at 10:33 AM Saeed Mahameed [off-list ref] wrote:

quoted

On Tue, 2020-09-15 at 15:04 +0800, Yunsheng Lin wrote:

quoted

On 2020/9/15 13:09, Saeed Mahameed wrote:

quoted

On Mon, 2020-09-14 at 20:06 +0800, Huazhong Tan wrote:

quoted

From: Yunsheng Lin <redacted>

Use napi_consume_skb() to batch consuming skb when cleaning
tx desc in NAPI polling.

Signed-off-by: Yunsheng Lin <redacted>
Signed-off-by: Huazhong Tan <redacted>
---
 drivers/net/ethernet/hisilicon/hns3/hns3_enet.c    | 27
+++++++++++-
----------
 drivers/net/ethernet/hisilicon/hns3/hns3_enet.h    |  2 +-
 drivers/net/ethernet/hisilicon/hns3/hns3_ethtool.c |  4 ++--
 3 files changed, 17 insertions(+), 16 deletions(-)

diff --git a/drivers/net/ethernet/hisilicon/hns3/hns3_enet.c

b/drivers/net/ethernet/hisilicon/hns3/hns3_enet.c
index 4a49a76..feeaf75 100644

--- a/drivers/net/ethernet/hisilicon/hns3/hns3_enet.c
+++ b/drivers/net/ethernet/hisilicon/hns3/hns3_enet.c

@@ -2333,10 +2333,10 @@ static int hns3_alloc_buffer(struct

hns3_enet_ring *ring,
 }

 static void hns3_free_buffer(struct hns3_enet_ring *ring,
-                      struct hns3_desc_cb *cb)
+                      struct hns3_desc_cb *cb, int budget)
 {
  if (cb->type == DESC_TYPE_SKB)
-         dev_kfree_skb_any((struct sk_buff *)cb->priv);
+         napi_consume_skb(cb->priv, budget);

This code can be reached from hns3_lb_clear_tx_ring() below which
is
your loopback test and called with non-zero budget, I am not sure
you
are allowed to call napi_consume_skb() with non-zero budget outside
napi context, perhaps the cb->type for loopback test is different
in lb
test case ? Idk.. , please double check other code paths.

Yes, loopback test may call napi_consume_skb() with non-zero budget
outside
napi context. Thanks for pointing out this case.

How about add the below WARN_ONCE() in napi_consume_skb() to catch
this
kind of error?

WARN_ONCE(!in_serving_softirq(), "napi_consume_skb() is called with
non-zero budget outside napi context");

Cc: Eric

I don't know, need to check performance impact.
And in_serving_softirq() doesn't necessarily mean in napi
but looking at _kfree_skb_defer(), i think it shouldn't care if napi or
not as long as it runs in soft irq it will push the skb to that
particular cpu napi_alloc_cache, which should be fine.

Yes, we only need to ensure _kfree_skb_defer() runs with automic context.

And it seems NAPI polling can be in thread context with BH disabled in below
patch, so in_softirq() checking should be more future-proof?

* in_softirq()   - We have BH disabled, or are processing softirqs

net: add support for threaded NAPI polling
https://www.mail-archive.com/netdev@vger.kernel.org/msg348491.html

quoted

Maybe instead of the WARN_ONCE just remove the budget condition and
replace it with

if (!in_serving_softirq())
      dev_consume_skb_any(skb);

Yes, that is good idea, _kfree_skb_defer() is only called in softirq or
BH disabled context, dev_consume_skb_any(skb) is called in other context,
so driver author do not need to worry about the calling context of the
napi_consume_skb().

quoted

I think we need to keep costs small.

So lets add a CONFIG_DEBUG_NET option so that developers can add
various DEBUG_NET() clauses.

Do you means something like below:

diff --git a/include/linux/netdevice.h b/include/linux/netdevice.h
index 157e024..61a6a62 100644
--- a/include/linux/netdevice.h
+++ b/include/linux/netdevice.h

@@ -5104,6 +5104,15 @@ do {								\
 })
 #endif

+#if defined(CONFIG_DEBUG_NET)
+#define DEBUG_NET_WARN(condition, format...)				\
+	do {								\
+		WARN(condition, ##__VA_ARGS__);
+	} while (0)
+#else
+#define DEBUG_NET_WARN(condition, format...)
+#endif
+
 /*
  *	The list of packet types we will receive (as opposed to discard)
  *	and the routines to invoke.

diff --git a/net/Kconfig b/net/Kconfig
index 3831206..f59ea4b 100644
--- a/net/Kconfig
+++ b/net/Kconfig

@@ -473,3 +473,9 @@ config HAVE_CBPF_JIT
 # Extended BPF JIT (eBPF)
 config HAVE_EBPF_JIT
 	bool
+
+config DEBUG_NET
+	bool
+	depends on DEBUG_KERNEL
+	help
+	  Say Y here to add some extra checks and diagnostics to networking.

diff --git a/net/core/skbuff.c b/net/core/skbuff.c
index bfd7483..10547db 100644
--- a/net/core/skbuff.c
+++ b/net/core/skbuff.c

@@ -904,6 +904,9 @@ void napi_consume_skb(struct sk_buff *skb, int budget)
 		return;
 	}

+	DEBUG_NET_WARN(!in_serving_softirq(),
+		        "napi_consume_skb() is called with non-zero budget outside softirq context");
+
 	if (!skb_unref(skb))
 		return;

.