Message ID | 1276520234.2478.82.camel@edumazet-laptop |
---|---|
State | Accepted, archived |
Delegated to: | David Miller |
Headers | show |
From: Eric Dumazet <eric.dumazet@gmail.com> Date: Mon, 14 Jun 2010 14:57:14 +0200 > [PATCH net-next-2.6] net: NET_SKB_PAD should depend on L1_CACHE_BYTES > > In old kernels, NET_SKB_PAD was defined to 16. > > Then commit d6301d3dd1c2 (net: Increase default NET_SKB_PAD to 32), and > commit 18e8c134f4e9 (net: Increase NET_SKB_PAD to 64 bytes) increased it > to 64. > > While first patch was governed by network stack needs, second was more > driven by performance issues on current hardware. Real intent was to > align data on a cache line boundary. > > So use max(32, L1_CACHE_BYTES) instead of 64, to be more generic. > > Remove microblaze and powerpc own NET_SKB_PAD definitions. > > Thanks to Alexander Duyck and David Miller for their comments. > > Suggested-by: David Miller <davem@davemloft.net> > Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com> Applied, thanks Eric. -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
diff --git a/arch/microblaze/include/asm/system.h b/arch/microblaze/include/asm/system.h index 48c4f03..81e1f7d 100644 --- a/arch/microblaze/include/asm/system.h +++ b/arch/microblaze/include/asm/system.h @@ -101,10 +101,7 @@ extern struct dentry *of_debugfs_root; * MicroBlaze doesn't handle unaligned accesses in hardware. * * Based on this we force the IP header alignment in network drivers. - * We also modify NET_SKB_PAD to be a cacheline in size, thus maintaining - * cacheline alignment of buffers. */ #define NET_IP_ALIGN 2 -#define NET_SKB_PAD L1_CACHE_BYTES #endif /* _ASM_MICROBLAZE_SYSTEM_H */ diff --git a/arch/powerpc/include/asm/system.h b/arch/powerpc/include/asm/system.h index a6297c6..6c294ac 100644 --- a/arch/powerpc/include/asm/system.h +++ b/arch/powerpc/include/asm/system.h @@ -515,11 +515,8 @@ __cmpxchg_local(volatile void *ptr, unsigned long old, unsigned long new, * powers of 2 writes until it reaches sufficient alignment). * * Based on this we disable the IP header alignment in network drivers. - * We also modify NET_SKB_PAD to be a cacheline in size, thus maintaining - * cacheline alignment of buffers. */ #define NET_IP_ALIGN 0 -#define NET_SKB_PAD L1_CACHE_BYTES #define cmpxchg64(ptr, o, n) \ ({ \ diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h index 122d083..ac74ee0 100644 --- a/include/linux/skbuff.h +++ b/include/linux/skbuff.h @@ -1414,12 +1414,14 @@ static inline int skb_network_offset(const struct sk_buff *skb) * * Various parts of the networking layer expect at least 32 bytes of * headroom, you should not reduce this. - * With RPS, we raised NET_SKB_PAD to 64 so that get_rps_cpus() fetches span - * a 64 bytes aligned block to fit modern (>= 64 bytes) cache line sizes + * + * Using max(32, L1_CACHE_BYTES) makes sense (especially with RPS) + * to reduce average number of cache lines per packet. + * get_rps_cpus() for example only access one 64 bytes aligned block : * NET_IP_ALIGN(2) + ethernet_header(14) + IP_header(20/40) + ports(8) */ #ifndef NET_SKB_PAD -#define NET_SKB_PAD 64 +#define NET_SKB_PAD max(32, L1_CACHE_BYTES) #endif extern int ___pskb_trim(struct sk_buff *skb, unsigned int len);