netdev - Re: [PATCH net-next v5 4/9] xen-netback: Change RX path for mapped SKB fragments

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Message-ID: <20140227160141.GJ16241@zion.uk.xensource.com>
Date:	Thu, 27 Feb 2014 16:01:41 +0000
From:	Wei Liu <wei.liu2@...rix.com>
To:	Zoltan Kiss <zoltan.kiss@...rix.com>
CC:	Wei Liu <wei.liu2@...rix.com>,
	Ian Campbell <Ian.Campbell@...rix.com>,
	<xen-devel@...ts.xenproject.org>, <netdev@...r.kernel.org>,
	<linux-kernel@...r.kernel.org>, <jonathan.davies@...rix.com>
Subject: Re: [PATCH net-next v5 4/9] xen-netback: Change RX path for mapped
 SKB fragments

On Thu, Feb 27, 2014 at 03:49:47PM +0000, Zoltan Kiss wrote:
> On 27/02/14 12:43, Wei Liu wrote:
> >On Mon, Feb 24, 2014 at 03:08:31PM +0000, Zoltan Kiss wrote:
> >>On 24/02/14 13:49, Zoltan Kiss wrote:
> >>>On 22/02/14 23:18, Zoltan Kiss wrote:
> >>>>On 18/02/14 17:45, Ian Campbell wrote:
> >>>>>On Mon, 2014-01-20 at 21:24 +0000, Zoltan Kiss wrote:
> >>>>>
> >>>>>Re the Subject: change how? Perhaps "handle foreign mapped pages on the
> >>>>>guest RX path" would be clearer.
> >>>>Ok, I'll do that.
> >>>>
> >>>>>
> >>>>>>RX path need to know if the SKB fragments are stored on
> >>>>>>pages from another
> >>>>>>domain.
> >>>>>Does this not need to be done either before the mapping change
> >>>>>or at the
> >>>>>same time? -- otherwise you have a window of a couple of commits where
> >>>>>things are broken, breaking bisectability.
> >>>>I can move this to the beginning, to keep bisectability. I've
> >>>>put it here originally because none of these makes sense without
> >>>>the previous patches.
> >>>Well, I gave it a close look: to move this to the beginning as a
> >>>separate patch I would need to put move a lot of definitions from
> >>>the first patch to here (ubuf_to_vif helper,
> >>>xenvif_zerocopy_callback etc.). That would be the best from bisect
> >>>point of view, but from patch review point of view even worse than
> >>>now. So the only option I see is to merge this with the first 2
> >>>patches, so it will be even bigger.
> >>Actually I was stupid, we can move this patch earlier and introduce
> >>stubs for those 2 functions. But for the another two patches (#6 and
> >>#8) it's still true that we can't move them before, only merge them
> >>into the main, as they heavily rely on the main patch. #6 is
> >>necessary for Windows frontends, as they are keen to send too many
> >>slots. #8 is quite a rare case, happens only if a guest wedge or
> >>malicious, and sits on the packet.
> >>So my question is still up: do you prefer perfect bisectability or
> >>more segmented patches which are not that pain to review?
> >>
> >
> >What's the diff stat if you merge those patches?
> >
> 
>  drivers/net/xen-netback/common.h    |   33 ++-
>  drivers/net/xen-netback/interface.c |   67 +++++-
>  drivers/net/xen-netback/netback.c   |  424
> ++++++++++++++++++++++-------------
>  3 files changed, 362 insertions(+), 162 deletions(-)

Not terribly bad IMHO -- if you look at netback's changelog, I've done
worse. :-P
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