| Message ID | 20230823-skb_ext-simplify-v2-1-66e26cd66860@weissschuh.net (mailing list archive) |
|---|---|
| State | Accepted |
| Commit | 5d21d0a65b573507bae774708199328b38dedfe6 |
| Delegated to: | Netdev Maintainers |
| Headers | show |
| Series | [net-next,v2] net: generalize calculation of skb extensions length | expand |
On Wed, Aug 23, 2023 at 11:28:38AM +0200, Thomas Weißschuh wrote: > Remove the necessity to modify skb_ext_total_length() when new extension > types are added. > Also reduces the line count a bit. > > With optimizations enabled the function is folded down to the same > constant value as before during compilation. > This has been validated on x86 with GCC 6.5.0 and 13.2.1. > Also a similar construct has been validated on godbolt.org with GCC 5.1. > In any case the compiler has to be able to evaluate the construct at > compile-time for the BUILD_BUG_ON() in skb_extensions_init(). > > Even if not evaluated at compile-time this function would only ever > be executed once at run-time, so the overhead would be very minuscule. > > Signed-off-by: Thomas Weißschuh <linux@weissschuh.net> Reviewed-by: Simon Horman <horms@kernel.org>
Hello: This patch was applied to netdev/net-next.git (main) by Jakub Kicinski <kuba@kernel.org>: On Wed, 23 Aug 2023 11:28:38 +0200 you wrote: > Remove the necessity to modify skb_ext_total_length() when new extension > types are added. > Also reduces the line count a bit. > > With optimizations enabled the function is folded down to the same > constant value as before during compilation. > This has been validated on x86 with GCC 6.5.0 and 13.2.1. > Also a similar construct has been validated on godbolt.org with GCC 5.1. > In any case the compiler has to be able to evaluate the construct at > compile-time for the BUILD_BUG_ON() in skb_extensions_init(). > > [...] Here is the summary with links: - [net-next,v2] net: generalize calculation of skb extensions length https://git.kernel.org/netdev/net-next/c/5d21d0a65b57 You are awesome, thank you!
diff --git a/net/core/skbuff.c b/net/core/skbuff.c index faa6c86da2a5..45707059082f 100644 --- a/net/core/skbuff.c +++ b/net/core/skbuff.c @@ -4785,23 +4785,13 @@ static const u8 skb_ext_type_len[] = { static __always_inline unsigned int skb_ext_total_length(void) { - return SKB_EXT_CHUNKSIZEOF(struct skb_ext) + -#if IS_ENABLED(CONFIG_BRIDGE_NETFILTER) - skb_ext_type_len[SKB_EXT_BRIDGE_NF] + -#endif -#ifdef CONFIG_XFRM - skb_ext_type_len[SKB_EXT_SEC_PATH] + -#endif -#if IS_ENABLED(CONFIG_NET_TC_SKB_EXT) - skb_ext_type_len[TC_SKB_EXT] + -#endif -#if IS_ENABLED(CONFIG_MPTCP) - skb_ext_type_len[SKB_EXT_MPTCP] + -#endif -#if IS_ENABLED(CONFIG_MCTP_FLOWS) - skb_ext_type_len[SKB_EXT_MCTP] + -#endif - 0; + unsigned int l = SKB_EXT_CHUNKSIZEOF(struct skb_ext); + int i; + + for (i = 0; i < ARRAY_SIZE(skb_ext_type_len); i++) + l += skb_ext_type_len[i]; + + return l; } static void skb_extensions_init(void)
Remove the necessity to modify skb_ext_total_length() when new extension types are added. Also reduces the line count a bit. With optimizations enabled the function is folded down to the same constant value as before during compilation. This has been validated on x86 with GCC 6.5.0 and 13.2.1. Also a similar construct has been validated on godbolt.org with GCC 5.1. In any case the compiler has to be able to evaluate the construct at compile-time for the BUILD_BUG_ON() in skb_extensions_init(). Even if not evaluated at compile-time this function would only ever be executed once at run-time, so the overhead would be very minuscule. Signed-off-by: Thomas Weißschuh <linux@weissschuh.net> --- Changes in v2: - Add more proof for identical behavior to the commit log - Link to v1: https://lore.kernel.org/r/20230822-skb_ext-simplify-v1-1-9dd047340ab5@weissschuh.net --- net/core/skbuff.c | 24 +++++++----------------- 1 file changed, 7 insertions(+), 17 deletions(-) --- base-commit: 90308679c297ffcbb317c715ef434e9fb3c881dc change-id: 20230822-skb_ext-simplify-3d93ceb95f62 Best regards,