Re: [PATCH 13/14] net: inline part of skb_csum_hwoffload_help

From: Pavel Begunkov
Date: Tue Jan 11 2022 - 15:52:23 EST


On 1/11/22 17:25, David Laight wrote:
From: Pavel Begunkov
Sent: 11 January 2022 16:59

On 1/11/22 09:24, David Laight wrote:
From: Pavel Begunkov
Sent: 11 January 2022 01:22

Inline a HW csum'ed part of skb_csum_hwoffload_help().

Signed-off-by: Pavel Begunkov <asml.silence@xxxxxxxxx>
---
include/linux/netdevice.h | 16 ++++++++++++++--
net/core/dev.c | 13 +++----------
2 files changed, 17 insertions(+), 12 deletions(-)

diff --git a/include/linux/netdevice.h b/include/linux/netdevice.h
index 3213c7227b59..fbe6c764ce57 100644
--- a/include/linux/netdevice.h
+++ b/include/linux/netdevice.h
@@ -4596,8 +4596,20 @@ void netdev_rss_key_fill(void *buffer, size_t len);

int skb_checksum_help(struct sk_buff *skb);
int skb_crc32c_csum_help(struct sk_buff *skb);
-int skb_csum_hwoffload_help(struct sk_buff *skb,
- const netdev_features_t features);
+int __skb_csum_hwoffload_help(struct sk_buff *skb,
+ const netdev_features_t features);
+
+static inline int skb_csum_hwoffload_help(struct sk_buff *skb,
+ const netdev_features_t features)
+{
+ if (unlikely(skb_csum_is_sctp(skb)))
+ return !!(features & NETIF_F_SCTP_CRC) ? 0 :

If that !! doing anything? - doesn't look like it.

It doesn't, but left the original style

It just makes you think it is needed...

+ skb_crc32c_csum_help(skb);
+
+ if (features & NETIF_F_HW_CSUM)
+ return 0;
+ return __skb_csum_hwoffload_help(skb, features);
+}

Maybe you should remove some bloat by moving the sctp code
into the called function.
This probably needs something like?

{
if (features & NETIF_F_HW_CSUM && !skb_csum_is_sctp(skb))
return 0;
return __skb_csum_hw_offload(skb, features);
}

I don't like inlining that sctp chunk myself. It seems your way would
need another skb_csum_is_sctp() in __skb_csum_hw_offload(), if so I
don't think it's worth it. Would've been great to put the
NETIF_F_HW_CSUM check first and hide sctp, but don't think it's
correct. Would be great to hear some ideas.

Given the definition:

static inline bool skb_csum_is_sctp(struct sk_buff *skb)
{
return skb->csum_not_inet;
}

I wouldn't worry about doing it twice.

Also skb_crc32_csum_help() is only called one.
Make it static (so inlined) and pass 'features' into it.

In reality sctp is such a slow crappy protocol that a few extra
function calls will make diddly-squit difference.
(And yes, we do actually use the sctp stack.)

I was more thinking about non-sctp path without NETIF_F_HW_CSUM


--
Pavel Begunkov