netdev - Re: [PATCH net-next V2] tun: introduce tx skb ring

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Message-ID: <5761418F.2050407@mojatatu.com>
Date:	Wed, 15 Jun 2016 07:52:47 -0400
From:	Jamal Hadi Salim <jhs@...atatu.com>
To:	Jason Wang <jasowang@...hat.com>, mst@...hat.com,
	netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
	kvm@...r.kernel.org, virtualization@...ts.linux-foundation.org,
	davem@...emloft.net
Cc:	eric.dumazet@...il.com, brouer@...hat.com
Subject: Re: [PATCH net-next V2] tun: introduce tx skb ring

On 16-06-15 04:38 AM, Jason Wang wrote:
> We used to queue tx packets in sk_receive_queue, this is less
> efficient since it requires spinlocks to synchronize between producer
> and consumer.
> 
> This patch tries to address this by:
> 
> - introduce a new mode which will be only enabled with IFF_TX_ARRAY
>    set and switch from sk_receive_queue to a fixed size of skb
>    array with 256 entries in this mode.
> - introduce a new proto_ops peek_len which was used for peeking the
>    skb length.
> - implement a tun version of peek_len for vhost_net to use and convert
>    vhost_net to use peek_len if possible.
> 
> Pktgen test shows about 18% improvement on guest receiving pps for small
> buffers:
> 
> Before: ~1220000pps
> After : ~1440000pps
> 

So this is more exercising the skb array improvements. For tun
it would be useful to see general performance numbers on user/kernel
crossing (i.e tun read/write).
If you have the cycles can you run such tests?

cheers,
jamal