linux-kernel - Re: [RFC PATCH V2 0/5] macvtap TX zero copy between guest and host kernel

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Date:	Mon, 14 Feb 2011 15:09:57 +0200
From:	"Michael S. Tsirkin" <mst@...hat.com>
To:	Shirley Ma <mashirle@...ibm.com>
Cc:	Avi Kivity <avi@...hat.com>, Arnd Bergmann <arnd@...db.de>,
	xiaohui.xin@...el.com, netdev@...r.kernel.org, kvm@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH V2 0/5] macvtap TX zero copy between guest and host
 kernel

On Fri, Dec 10, 2010 at 01:51:31AM -0800, Shirley Ma wrote:
> This patchset add supports for TX zero-copy between guest and host
> kernel through vhost. It significantly reduces CPU utilization on the
> local host on which the guest is located (It reduced 30-50% CPU usage
> for vhost thread for single stream test). The patchset is based on
> previous submission and comments from the community regarding when/how
> to handle guest kernel buffers to be released. This is the simplest
> approach I can think of after comparing with several other solutions.
> 
> This patchset includes:
> 
> 1. Induce a new sock zero-copy flag, SOCK_ZEROCOPY;
> 
> 2. Induce a new device flag, NETIF_F_ZEROCOPY for device can support
> zero-copy;
> 
> 3. Add a new struct skb_ubuf_info in skb_share_info for userspace
> buffers release callback when device DMA has done for that skb;
> 
> 4. Add vhost zero-copy callback in vhost when skb last refcnt is gone;
>    add vhost_zerocopy_add_used_and_signal to notify guest to release TX
> skb buffers.
> 
> 5. Add macvtap zero-copy in lower device when sending packet is greater
> than 128 bytes.
> 
> The patchset has passed netperf/netserver test on Chelsio, and
> continuing test on other 10GbE NICs, like Intel ixgbe, Mellanox mlx4...
> I will provide guest to host, host to guest performance data next week.
> 
> However when running stress test, vhost & virtio_net seems out of sync,
> and virito_net interrupt was disabled somehow, and it stopped to send
> any packet. This problem has bothered me for a long long time, I will
> continue to look at this.
> 
> Please review this.
> 
> Thanks
> Shirley

What's the status here?  Since there are core net changes, we'll need to
see the final version soon if it's to appear in 2.6.39.

Could the problem be related to the patch
	virtio_net: Add schedule check to napi_enable call
?
Also, I expect there should be driver patches for some
devices? Where are they?

Thanks,

-- 
MST
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