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

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Message-ID: <20110311092403.3aaca41c@nehalam>
Date:	Fri, 11 Mar 2011 09:24:03 -0800
From:	Stephen Hemminger <shemminger@...tta.com>
To:	Ian Campbell <Ian.Campbell@...citrix.com>
Cc:	Ben Hutchings <bhutchings@...arflare.com>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	xen-devel <xen-devel@...ts.xensource.com>,
	Jeremy Fitzhardinge <jeremy@...p.org>,
	Herbert Xu <herbert@...dor.apana.org.au>,
	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
	Francois Romieu <romieu@...zoreil.com>
Subject: Re: [GIT/PATCH v4] xen network backend driver

On Fri, 11 Mar 2011 10:22:55 +0000
Ian Campbell <Ian.Campbell@...citrix.com> wrote:

> On Thu, 2011-03-10 at 17:30 +0000, Ben Hutchings wrote:
> > 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@...rix.com> 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.
> 
> Will do.
>  
> > > 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.
> 
> Agreed.
> 
> > 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.
> 
> Is there an example of a driver which also updates the stats on the
> datapath?
> 
> If it's ok I'd prefer to defer this change for now though.

Sure, my original comment was just a hint for future.


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