netdev - Re: [RFC PATCH v2 00/10] udp: implement GRO support

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Message-ID: <20181024105514.GR3823@gauss3.secunet.de>
Date:   Wed, 24 Oct 2018 12:55:14 +0200
From:   Steffen Klassert <steffen.klassert@...unet.com>
To:     Paolo Abeni <pabeni@...hat.com>
CC:     <netdev@...r.kernel.org>, Willem de Bruijn <willemb@...gle.com>
Subject: Re: [RFC PATCH v2 00/10] udp: implement GRO support

On Tue, Oct 23, 2018 at 02:22:12PM +0200, Paolo Abeni wrote:
> On Tue, 2018-10-23 at 14:10 +0200, Steffen Klassert wrote:
> 
> > Some quick benchmark numbers with UDP packet forwarding
> > (1460 byte packets) through two gateways:
> > 
> > net-next: 16.4 Gbps
> > 
> > net-next + UDP GRO: 20.3 Gbps
> 
> uhmmm... what do you think about this speed-up ?

skb_segment() burns a lot of cycles. If I do the same test with
TCP and disable HW TSO, throughput drops also down to similar
values.

In case of software segmentation, the skb chain appropach
is likely faster because packets are not mangled. So no need
to allocate skbs, no new checksum calculations, less memcpy etc.

If we have an early route lookup in GRO, we could have a good
guess on the offload capabilities of the outgoing device.
So in case that software segmentation is likely, use the
skb chaining method. If HW segmentation is likely, merge
IP packets.

The chaining method might be also faster on non UDP GRO enabled
sockets.

I'll try to implement the skb chaining method on top of this
to see what we get from that.