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Re: [Qemu-devel] [PATCH] rtl8139: flush queued packets when RxBufPtr is

From: Stefan Hajnoczi
Subject: Re: [Qemu-devel] [PATCH] rtl8139: flush queued packets when RxBufPtr is written
Date: Fri, 24 May 2013 16:34:24 +0200
User-agent: Mutt/1.5.21 (2010-09-15)

On Wed, May 22, 2013 at 02:50:18PM +0200, Stefan Hajnoczi wrote:
> Net queues support efficient "receive disable".  For example, tap's file
> descriptor will not be polled while its peer has receive disabled.  This
> saves CPU cycles for needlessly copying and then dropping packets which
> the peer cannot receive.
> rtl8139 is missing the qemu_flush_queued_packets() call that wakes the
> queue up when receive becomes possible again.
> As a result, the Windows 7 guest driver reaches a state where the
> rtl8139 cannot receive packets.  The driver has actually refilled the
> receive buffer but we never resume reception.
> The bug can be reproduced by running a large FTP 'get' inside a Windows
> 7 guest:
>   $ qemu -netdev tap,id=tap0,...
>          -device rtl8139,netdev=tap0
> The Linux guest driver does not trigger the bug, probably due to a
> different buffer management strategy.
> Reported-by: Oliver Francke <address@hidden>
> Signed-off-by: Stefan Hajnoczi <address@hidden>
> ---
>  hw/net/rtl8139.c | 3 +++
>  1 file changed, 3 insertions(+)

Applied to my net tree:


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