netdev - Re: [RFC PATCH V4 12/13] netfront: multi page ring support.

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Date:	Thu, 16 Feb 2012 10:16:19 +0000
From:	Wei Liu <wei.liu2@...rix.com>
To:	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
CC:	<wei.liu2@...rix.com>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	"xen-devel@...ts.xensource.com" <xen-devel@...ts.xensource.com>,
	"Ian Campbell" <Ian.Campbell@...rix.com>
Subject: Re: [RFC PATCH V4 12/13] netfront: multi page ring support.

On Thu, 2012-02-16 at 10:02 +0000, Wei Liu (Intern) wrote:
> On Wed, 2012-02-15 at 22:42 +0000, Konrad Rzeszutek Wilk wrote:
> > On Thu, Feb 02, 2012 at 04:49:22PM +0000, Wei Liu wrote:
> > > 
> > > Signed-off-by: Wei Liu <wei.liu2@...rix.com>
> > 
> > It also needs this:
> > 
> > From 4cf97c025792cf073edc4d312b962ecc0b3b67ab Mon Sep 17 00:00:00 2001
> > From: Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
> > Date: Wed, 15 Feb 2012 17:39:46 -0500
> > Subject: [PATCH] xen/net: Don't try to use all of the rings if we are not
> >  built for it.
> > 
> > Otherwise we end up:
> > 
> > BUG: unable to handle kernel paging request at ffff88004000c0c8
> > IP: [<ffffffff810f1ee4>] free_one_page+0x144/0x410
> > PGD 1806063 PUD 0
> > 22:22:34 tst007 logger: /etc/xen/scripts/vif-bridge: offline XENBUS_PATH=backend/vif/1/0
> > 00 [#1] SMP
> > CPU 0
> > Modules linked in:
> > 
> > Pid: 17, comm: xenwatch Not tainted 3.2.0upstream #2 Xen HVM domU
> > RIP: 0010:[<ffffffff810f1ee4>]  [<ffffffff810f1ee4>] free_one_page+0x144/0x410
> > RSP: 0018:ffff88003bea3c40  EFLAGS: 00010046
> > .. snip.
> > Call Trace:
> >  [<ffffffff810f2c7f>] __free_pages_ok+0x9f/0xe0
> >  [<ffffffff810f4eab>] __free_pages+0x1b/0x40
> >  [<ffffffff810f4f1a>] free_pages+0x4a/0x60
> >  [<ffffffff8138b33d>] xennet_disconnect_backend+0xbd/0x130
> >  [<ffffffff8138bd88>] talk_to_netback+0x8e8/0x1160
> >  [<ffffffff812f4e28>] ? xenbus_gather+0xd8/0x170
> >  [<ffffffff8138e3bd>] netback_changed+0xcd/0x550
> >  [<ffffffff812f5bb8>] xenbus_otherend_changed+0xa8/0xb0
> > 
> > Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
> > ---
> >  drivers/net/xen-netfront.c |   14 +++++++++++++-
> >  1 files changed, 13 insertions(+), 1 deletions(-)
> > 
> > diff --git a/drivers/net/xen-netfront.c b/drivers/net/xen-netfront.c
> > index 0223552..1eadd90 100644
> > --- a/drivers/net/xen-netfront.c
> > +++ b/drivers/net/xen-netfront.c
> > @@ -29,6 +29,8 @@
> >   * IN THE SOFTWARE.
> >   */
> >  
> > +#define DEBUG 1
> > +
> >  #include <linux/module.h>
> >  #include <linux/kernel.h>
> >  #include <linux/netdevice.h>
> > @@ -66,7 +68,7 @@ struct netfront_cb {
> >  
> >  #define GRANT_INVALID_REF	0
> >  
> > -#define XENNET_MAX_RING_PAGE_ORDER 2
> > +#define XENNET_MAX_RING_PAGE_ORDER 4
> 
> I guess this is you tuning with page order? And here is not the only one
> place you changed?
> 
> As a matter of fact, in the previous patch 8 I encode hard limit 2 on
> the ring page order, your change here will stop FE / BE from connecting.
> 
> I think I will also need to change this to something like
> 
>   #define XENNET_MAX_RING_PAGE_ORDER XENBUS_MAX_RING_PAGE_ORDER
> 
> to remind people to modify that value. 
> 

To be more precise on this, tangling with RING_PAGE_ORDER will not
affect FE, because the mapping is done in BE. However if you make
RING_PAGE_ORDER larger than BE limit, it will fail.

So the above #define is actually asking people playing with FE to check
BE limit. :-(


Wei.

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