RE: e1000 performance hack for ppc64 (Power4)

From: Dave Hansen (
Date: Fri Jun 13 2003 - 11:21:03 EST

Too long to quote:

Wouldn't you get most of the benefit from copying that stuff around in
the driver if you allocated the skb->data aligned in the first place?

There's already code to align them on CPU cache boundaries:
#define SKB_DATA_ALIGN(X) (((X) + (SMP_CACHE_BYTES - 1)) & \
                                 ~(SMP_CACHE_BYTES - 1))

So, do something like this:
#define SKB_DATA_ALIGN(X) (((X) + (ARCH_ALIGN_SKB - 1)) & \
                                 ~(SKB_ALIGN_BYTES - 1))

You could easily make this adaptive to no align on th arch size when the
request is bigger than that, just like in the e1000 patch you posted.

Dave Hansen

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