netdev - Re: [Qemu-devel] [PATCH] net: add raw backend

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Message-ID: <4A65A0FC.6090204@Voltaire.com>
Date:	Tue, 21 Jul 2009 14:05:32 +0300
From:	Or Gerlitz <ogerlitz@...taire.com>
To:	"Michael S. Tsirkin" <mst@...hat.com>
CC:	Herbert Xu <herbert@...dor.apana.org.au>,
	Jamie Lokier <jamie@...reable.org>,
	Anthony Liguori <anthony@...emonkey.ws>, qemu-devel@...gnu.org,
	Jan Kiszka <jan.kiszka@....de>,
	Mark McLoughlin <markmc@...hat.com>,
	Dor Laor <dlaor@...hat.com>, netdev@...r.kernel.org
Subject: Re: [Qemu-devel] [PATCH] net: add raw backend  - some performance
 measurements

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?

Michael, 

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

Or.

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