linux-kernel - Re: [PATCH net-next V2 2/2] virtio-net: coalesce rx frags when possible during rx

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Date:	Thu, 31 Oct 2013 06:57:52 -0700
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Jason Wang <jasowang@...hat.com>
Cc:	davem@...emloft.net, edumazet@...gle.com,
	linux-kernel@...r.kernel.org, netdev@...r.kernel.org,
	rusty@...tcorp.com.au, mst@...hat.com, mwdalton@...gle.com,
	virtualization@...ts.linux-foundation.org, kmindg@...il.com
Subject: Re: [PATCH net-next V2 2/2] virtio-net: coalesce rx frags when
 possible during rx

On Thu, 2013-10-31 at 19:47 +0800, Jason Wang wrote:
> Commit 2613af0ed18a11d5c566a81f9a6510b73180660a (virtio_net: migrate mergeable
> rx buffers to page frag allocators) try to increase the payload/truesize for
> MTU-sized traffic. But this will introduce the extra overhead for GSO packets
> received because of the frag list. This commit tries to reduce this issue by
> coalesce the possible rx frags when possible during rx. Test result shows the
> about 15% improvement on full size GSO packet receiving (and even better than
> commit 2613af0ed18a11d5c566a81f9a6510b73180660a).
> 
> Before this commit:
> ./netperf -H 192.168.100.4
> MIGRATED TCP STREAM TEST from 0.0.0.0 (0.0.0.0) port 0 AF_INET to 192.168.100.4
> () port 0 AF_INET : demo
> Recv   Send    Send
> Socket Socket  Message  Elapsed
> Size   Size    Size     Time     Throughput
> bytes  bytes   bytes    secs.    10^6bits/sec
> 
>  87380  16384  16384    10.00    20303.87
> 
> After this commit:
> ./netperf -H 192.168.100.4
> MIGRATED TCP STREAM TEST from 0.0.0.0 (0.0.0.0) port 0 AF_INET to 192.168.100.4 () port 0 AF_INET : demo
> Recv   Send    Send
> Socket Socket  Message  Elapsed
> Size   Size    Size     Time     Throughput
> bytes  bytes   bytes    secs.    10^6bits/sec
> 
>  87380  16384  16384    10.00    23841.26
> 
> Cc: Rusty Russell <rusty@...tcorp.com.au>
> Cc: Michael S. Tsirkin <mst@...hat.com>
> Cc: Michael Dalton <mwdalton@...gle.com>
> Cc: Eric Dumazet <edumazet@...gle.com>
> Acked-by: Michael S. Tsirkin <mst@...hat.com>
> Signed-off-by: Jason Wang <jasowang@...hat.com>
> ---

Excellent !

We now have 2 or 3 frags per skb, like tcp stack manages to do on output
path.

Michael Dalton is also working on a autotuning patch, using an EWMA, so
that the size of individual sg blocks can vary from 1500 to 4096, this
might show even better throughput, we'll see.

Acked-by: Eric Dumazet <edumazet@...gle.com>



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