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[NET]: Allow skb headroom to be overridden

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Previously we added NET_IP_ALIGN so an architecture can override the
padding done to align headers. The next step is to allow the skb
headroom to be overridden.

We currently always reserve 16 bytes to grow into, meaning all DMAs
start 16 bytes into a cacheline. On ppc64 we really want DMA writes to
start on a cacheline boundary, so we increase that headroom to one
cacheline.

Signed-off-by: Anton Blanchard <anton@samba.org>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Anton Blanchard
2006-03-31 02:27:06 -08:00
committed by David S. Miller
parent 0803dbed7a
commit 025be81e83
2 changed files with 29 additions and 5 deletions
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5
include/asm-powerpc/system.h
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@ -365,8 +365,11 @@ __cmpxchg(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_IP_ALIGN 0
#define NET_SKB_PAD L1_CACHE_BYTES
#endif
#define arch_align_stack(x) (x)