From mboxrd@z Thu Jan  1 00:00:00 1970
From: Dor Laor <dor.laor@qumranet.com>
Subject: Re: [PATCH 3/3] Stop dropping so many RX packets in tap
	(v2)
Date: Mon, 05 May 2008 01:13:49 +0300
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Cc: kvm-devel@lists.sourceforge.net,
	Marcelo Tosatti <mtosatti@redhat.com>, Avi Kivity <avi@qumranet.com>
To: Anthony Liguori <aliguori@us.ibm.com>
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On Sun, 2008-05-04 at 15:21 -0500, Anthony Liguori wrote:
> Normally, tap always reads packets and simply lets the client drop them if it
> cannot receive them.  For virtio-net, this results in massive packet loss and
> about an 80% performance loss in TCP throughput.
> 
> This patch modifies qemu_send_packet() to only deliver a packet to a VLAN
> client if it doesn't have a fd_can_read method or the fd_can_read method
> indicates that it can receive packets.  We also return a status of whether
> any clients were able to receive the packet.
> 
> If no clients were able to receive a packet, we buffer the packet until a
> client indicates that it can receive packets again.
> 
> This patch also modifies the tap code to only read from the tap fd if at least
> one client on the VLAN is able to receive a packet.
> 
> Finally, this patch changes the tap code to drain all possible packets from
> the tap device when the tap fd is readable.
> 
> Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>

Patchset looks good and reduces some nasty hacks. It probably also
improves other devices like e1000 et al.
Cheers,
Dor


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