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[Xen-devel] Re: [GIT/PATCH v4] xen network backend driver

To: Stephen Hemminger <shemminger@xxxxxxxxxx>
Subject: [Xen-devel] Re: [GIT/PATCH v4] xen network backend driver
From: Ben Hutchings <bhutchings@xxxxxxxxxxxxxx>
Date: Thu, 10 Mar 2011 17:30:13 +0000
Cc: Fitzhardinge <jeremy@xxxxxxxx>, xen-devel <xen-devel@xxxxxxxxxxxxxxxxxxx>, Jeremy, Ian Campbell <Ian.Campbell@xxxxxxxxxx>, Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>, "netdev@xxxxxxxxxxxxxxx" <netdev@xxxxxxxxxxxxxxx>, Francois Romieu <romieu@xxxxxxxxxxxxx>, Herbert Xu <herbert@xxxxxxxxxxxxxxxxxxx>
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On Thu, 2011-03-10 at 09:15 -0800, Stephen Hemminger wrote:
> On Thu, 10 Mar 2011 17:02:33 +0000
> Ian Campbell <Ian.Campbell@xxxxxxxxxx> wrote:
> > +struct xenvif {
> > +   /* Unique identifier for this interface. */
> ...
> > +   struct net_device_stats stats;
> > +
> There is already a stats struct in net_device in current kernel
> versions, unless there is a compelling reason otherwise
> please use that.
> Also, you probably want to implement per-cpu and 64 bit
> stats.

The driver is using a single queue, so I don't see what benefit it would
get from per-cpu stats.  At some point it should become multiqueue and
then it should store per-queue stats.

64-bit stats are definitely preferable, but since they're being
maintained on the data path this may require some significant work.
(Ian: see <linux/u64_stats_sync.h> for the canonical way to do this.)
Given that only a relatively few existing drivers do this (I count 13),
I'm not sure we can reasonably demand that a new driver does - yet.


Ben Hutchings, Senior Software Engineer, Solarflare
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