Re: [PATCHv11] vhost: vhost TX zero-copy support
From: David Miller
Date: Mon Jul 18 2011 - 13:43:50 EST
From: "Michael S. Tsirkin" <mst@xxxxxxxxxx>
Date: Mon, 18 Jul 2011 16:48:46 +0300
>>From: Shirley Ma <mashirle@xxxxxxxxxx>
> This adds experimental zero copy support in vhost-net,
> disabled by default. To enable, set
> experimental_zcopytx module option to 1.
> This patch maintains the outstanding userspace buffers in the
> sequence it is delivered to vhost. The outstanding userspace buffers
> will be marked as done once the lower device buffers DMA has finished.
> This is monitored through last reference of kfree_skb callback. Two
> buffer indices are used for this purpose.
> The vhost-net device passes the userspace buffers info to lower device
> skb through message control. DMA done status check and guest
> notification are handled by handle_tx: in the worst case is all buffers
> in the vq are in pending/done status, so we need to notify guest to
> release DMA done buffers first before we get any new buffers from the
> One known problem is that if the guest stops submitting
> buffers, buffers might never get used until some
> further action, e.g. device reset. This does not
> seem to affect linux guests.
> Signed-off-by: Shirley <xma@xxxxxxxxxx>
> Signed-off-by: Michael S. Tsirkin <mst@xxxxxxxxxx>
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