netdev - Re: [PATCHv3 0/6] tun zerocopy support

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Date:	Sun, 22 Jul 2012 12:40:20 -0700 (PDT)
From:	David Miller <davem@...emloft.net>
To:	mst@...hat.com
Cc:	jasowang@...hat.com, eric.dumazet@...il.com,
	netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
	ebiederm@...ssion.com, Ian.Campbell@...rix.com
Subject: Re: [PATCHv3 0/6] tun zerocopy support

From: "Michael S. Tsirkin" <mst@...hat.com>
Date: Sun, 22 Jul 2012 01:05:34 +0300

> I agree a small win in CPU use is nothing to write home about,
> I don't yet understand why the win is so small - macvtap has zero copy
> supported for a while and it has exactly same issues.
> I hope adding tun zerocopy support upstream will help us
> make progress faster and find the bottleneck, so far not many people use
> macvtap so zero copy mode there didn't make progress.
> 
> I do know why local performance regresses with zero copy enabled:
> instead of plain copy to user we got get user pages and then memcpy.
> We'll need some logic here to detect this and turn off zero copy.
> 
> The core patches will also be helpful for Ian's more ambitious work.
> 
> Overall I think it's a step in the right direction and it's easier to
> work if core parts are upstream, but if you think we need to wait
> until the gains are more significant, I understand that too.

Ok, I've applied this series, let's see what happens.
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