netdev - Re: [PATCH net-next] net: use indirect call wrappers for skb_copy_datagram

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Message-ID: <2b5f096a143f4dea9c9a2896913d8ca79688b00f.camel@redhat.com>
Date:   Wed, 25 Mar 2020 17:00:02 +0100
From:   Paolo Abeni <pabeni@...hat.com>
To:     Willem de Bruijn <willemdebruijn.kernel@...il.com>
Cc:     Eric Dumazet <edumazet@...gle.com>,
        "David S . Miller" <davem@...emloft.net>,
        netdev <netdev@...r.kernel.org>,
        Eric Dumazet <eric.dumazet@...il.com>
Subject: Re: [PATCH net-next] net: use indirect call wrappers for
 skb_copy_datagram_iter()

On Wed, 2020-03-25 at 10:55 -0400, Willem de Bruijn wrote:
> On the UDP front this reminded me of another indirect function call
> without indirect call wrapper: getfrag in __ip_append_data.
> 
> That is called for each datagram once per linear + once per page. That
> said, the noise in my quick RR test was too great to measure any
> benefit from the following. 

Why an RR test ?

I think you should be able to measure some raw tput improvement with
large UDP GSO write towards a blackhole dst/or dropping ingress pkts
with XDP (just to be sure the bottle-neck is on the sender side).

> Paolo, did you happen to also look at that
> when introducing the indirect callers? Seems like it won't hurt to
> add.

Nope, sorry I haven't experimented that.

For the record, I have 2 others item on my list, I hope to have time to
process some day: the ingress dst->input and the default ->enqueue  and
->dequeue

Cheers,

Paolo

p.s. feel free to move this on a different thread, as it fit you better