Re: skb data uncacheable ??

From: Nagendra Singh Tomar
Date: Tue Apr 13 2004 - 23:22:24 EST

On Tue, 13 Apr 2004, Henrik Nordstrom wrote:

> On Tue, 13 Apr 2004, Nagendra Singh Tomar wrote:
> > even for devices that do Rx checksum verification (and hence allow us to
> > leave the data payload untouched). If we can have a strategy in which we
> > keep first 128 bytes say (precisely max possible header size) in a
> > cacheable region and the rest, that is pure data, in uncacheable region,
> > we can see some gain.
> This should not be difficult if using non-linear sk_buff.

You are right, but when I was writing this mail I had non-SG devices in
mind. Even for a regular ethernet frame of 1500 bytes we can gain a lot
if can put the data portion in noncacheable region.

> > The most important question: Is it worth all this ? DO we gain much if we
> > prevent pollution of the data cache, by doing these tricks.
> I am doubtful, but I am possibly biased from working a lot with iptables
> and often accessing the payload while the packet is forwarded for NAT
> etc.. but maybe.

If the data payload has to be touched in anyway then putting it in
noncacheable area will turn to be a killer.

> Regards
> Henrik


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