On Mon, 15 May 2006 14:39:23 -0700 Rick Jones <[EMAIL PROTECTED]> wrote:
> David S. Miller wrote: > > From: "Randy.Dunlap" <[EMAIL PROTECTED]> > > Date: Mon, 15 May 2006 08:02:58 -0700 > > > > > >>>-#define NETDEV_ALIGN 32 > >>>+#define NETDEV_ALIGN L1_CACHE_BYTES > >>> #define NETDEV_ALIGN_CONST (NETDEV_ALIGN - 1) > >> > >>I don't know about the fixed value of 32, but if this patch is > >>accepted, I'd prefer NETDEV_ALIGN_MASK instead of NETDEV_ALIGN_CONST. > > > > > > The reason it's 32 is that old drivers depended on the > > struct being at least 32-byte aligned because they would > > embed structures DMA'd to/from the card in their private > > area and just assumed that would be aligned enough for > > the card's restrictions. > > > > So setting it to L1_CACHE_BYTES would be wrong, because if > > that happens to be less than 32 it would violate said > > assumption which we are catering to. > > How about: > > #define NETDEV_ALIGN_MIN 32 > #if L1_CACHE_BYTES > NETDEV_ALIGN_MIN > # define NETDEV_ALIGN L1_CACHE_BYTES > #else > # define NETDEV_ALIGN NETDEV_ALIGN_MIN > #endif > I can't see how adding more padding could help performance here. Most drivers reference both parts (netdevice and netdev_priv) in most code paths. So having the stuff on separate cache lines couldn't help that much. Alternatively, there might be a performance gain if the netdevice stats structure was rearranged so the rx and tx stats were on different cache lines. - To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html
