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Re: [Qemu-devel] [PATCH] net: add raw backend - some performance measur

From: Or Gerlitz
Subject: Re: [Qemu-devel] [PATCH] net: add raw backend - some performance measurements
Date: Tue, 21 Jul 2009 14:05:32 +0300
User-agent: Thunderbird (X11/20081209)

Michael S. Tsirkin wrote:
> With raw sockets, send will block or fail if the TX queue for device is
> full. With tap+bridge, the buffer in tap has to fill up instead, which
> is not the same. I'm not sure this is the issue here, but could be: the
> benchmark is UDP, isn't it?


What/where is this tap buffer? we're talking on VM TX, so looking on 
tun_get_user I see a call to 
skb_copy_datagram_from_iovec() to copy from the user buffer to an skb, then a 
call to netif_rx_ni() and that's it... As for your question, indeed udp, the VM 
runs netperf/UDP_STREAM


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