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SubjectRe: Speed of memcpy, csum_partial and csum_partial_copy


On Sat, 8 Jun 1996, Alan Cox wrote:
>
> > In short, the two copies that occur in TCP loopback (first from the
> > sender into the kernel, and then from the kernel into the receiver) alone
> > account for 60% of the TCP stack..
>
> There are three for TCP loopback unless someone has fiddled recently.

Umm.. Why do you think the TCP performance jumped from 3.4MB/s to 12MB/s
on my old P100?

Yes, I "fiddled" with it (the larger MTU did a lot, but if you think the
larger MTU in 2.0 is the only thing that's changed, you're wrong).

> We copy
>
> user->sk_buff [with csum]
> sk_buff to sk_buff
> sk_buff->user [skip csum]

Nope. The sk_buff->sk_buff is just a "skb_clone()", no copy.

Linus


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