linux-kernel - Re: [PATCH net-next] xen-netback: Adding debugfs "io_ring

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Date:	Wed, 2 Jul 2014 19:58:55 +0100
From:	Ian Campbell <Ian.Campbell@...rix.com>
To:	Zoltan Kiss <zoltan.kiss@...rix.com>
CC:	Wei Liu <wei.liu2@...rix.com>, <netdev@...r.kernel.org>,
	<linux-kernel@...r.kernel.org>, <xen-devel@...ts.xenproject.org>
Subject: Re: [PATCH net-next] xen-netback: Adding debugfs "io_ring_qX" files

On Wed, 2014-07-02 at 19:43 +0100, Zoltan Kiss wrote:
> On 02/07/14 11:56, Ian Campbell wrote:
> > On Mon, 2014-06-30 at 21:33 +0100, Zoltan Kiss wrote:
> >> This patch adds debugfs capabilities to netback. There used to be a similar
> >> patch floating around for classic kernel, but it used procfs. It is based on a
> >> very similar blkback patch.
> >> It creates xen-netback/[vifname]/io_ring_q[queueno] files, reading them output
> >> various ring variables etc. Writing "kick" into it imitates an interrupt
> >> happened, it can be useful to check whether the ring is just stalled due to a
> >> missed interrupt.
> >
> > Shouldn't there be some CONFIG_XEN_DEBUG_FS ifdefs sprinkled around
> > here?
> 
> Good question! I've checked where else is this used, it is in 
> arch/x86/xen, particularly in spinlock.c and p2m.c. The goal there is, 
> as far as I see, to make it configurable whether you want debugging in 
> fast path. However here in netback it's not fast path.
> It would be nice to have this netback debugfs stuff in production 
> systems, but if it is tied to this same config option, that wouldn't be 
> possible.
> So either we don't put it behind a config option, or create a whole new 
> one just for this. I don't see the benefit of the latter one, so I would 
> prefer keep it like it is now.

Sorry, I meant CONFIG_DEBUG_FS (i.e. the top level option for the whole
debugfs thing being available at all) but I cut-n-pasted the wrong
thing.

Ian.

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