linux-kernel - Re: [PATCH] virtio_net: introduce VIRTIO_NET_HDR_F_DATA

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Message-Id: <20110611.155802.495936379311916892.davem@davemloft.net>
Date:	Sat, 11 Jun 2011 15:58:02 -0700 (PDT)
From:	David Miller <davem@...emloft.net>
To:	mst@...hat.com
Cc:	jasowang@...hat.com, rusty@...tcorp.com.au, netdev@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	virtualization@...ts.linux-foundation.org, yvugenfi@...hat.com,
	kvm@...r.kernel.org, herbert@...dor.hengli.com.au
Subject: Re: [PATCH] virtio_net: introduce VIRTIO_NET_HDR_F_DATA_VALID

From: "Michael S. Tsirkin" <mst@...hat.com>
Date: Fri, 10 Jun 2011 14:28:28 +0300

> On Fri, Jun 10, 2011 at 06:56:17PM +0800, Jason Wang wrote:
>> There's no need for the guest to validate the checksum if it have been
>> validated by host nics. So this patch introduces a new flag -
>> VIRTIO_NET_HDR_F_DATA_VALID which is used to bypass the checksum
>> examing in guest. The backend (tap/macvtap) may set this flag when
>> met skbs with CHECKSUM_UNNECESSARY to save cpu utilization.
>> 
>> No feature negotiation is needed as old driver just ignore this flag.
> 
> This wasn't required by the spec, but maybe it should be.
> 
>> Iperf shows 12%-30% performance improvement for UDP traffic. For TCP,
>> when gro is on no difference as it produces skb with partial
>> checksum. But when gro is disabled, 20% or even higher improvement
>> could be measured by netperf.
>> 
>> Signed-off-by: Jason Wang <jasowang@...hat.com>
> 
> 
> Acked-by: Michael S. Tsirkin <mst@...hat.com>

Applied to net-next-2.6
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