linux-kernel - Re: [PATCH v5 00/10] xen-block: multi hardware-queues/rings support

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Date:	Wed, 25 Nov 2015 17:12:34 -0500
From:	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
To:	Bob Liu <bob.liu@...cle.com>
Cc:	xen-devel@...ts.xen.org, linux-kernel@...r.kernel.org,
	roger.pau@...rix.com, felipe.franciosi@...rix.com, axboe@...com,
	avanzini.arianna@...il.com, rafal.mielniczuk@...rix.com,
	jonathan.davies@...rix.com, david.vrabel@...rix.com
Subject: Re: [PATCH v5 00/10] xen-block: multi hardware-queues/rings support

On Wed, Nov 25, 2015 at 03:56:03PM -0500, Konrad Rzeszutek Wilk wrote:
> On Wed, Nov 25, 2015 at 02:25:07PM -0500, Konrad Rzeszutek Wilk wrote:
> > >   xen/blkback: separate ring information out of struct xen_blkif
> > >   xen/blkback: pseudo support for multi hardware queues/rings
> > >   xen/blkback: get the number of hardware queues/rings from blkfront
> > >   xen/blkback: make pool of persistent grants and free pages per-queue
> > 
> > OK, got to those as well. I have put them in 'devel/for-jens-4.5' and
> > are going to test them overnight before pushing them out.
> > 
> > I see two bugs in the code that we MUST deal with:
> > 
> >  - print_stats () is going to show zero values.
> >  - the sysfs code (VBD_SHOW) aren't converted over to fetch data
> >    from all the rings.
> 
> - kthread_run can't handle the two "name, i" arguments. I see:
> 
> root      5101     2  0 20:47 ?        00:00:00 [blkback.3.xvda-]
> root      5102     2  0 20:47 ?        00:00:00 [blkback.3.xvda-]

And doing save/restore:

xl save <id> /tmp/A;
xl restore /tmp/A;

ends up us loosing the proper state and not getting the ring setup back.
I see this is backend:

[ 2719.448600] vbd vbd-22-51712: -1 guest requested 0 queues, exceeding the maximum of 3.

And XenStore agrees:
tool = ""
 xenstored = ""
local = ""
 domain = ""
  0 = ""
   domid = "0"
   name = "Domain-0"
   device-model = ""
    0 = ""
     state = "running"
   error = ""
    backend = ""
     vbd = ""
      2 = ""
       51712 = ""
        error = "-1 guest requested 0 queues, exceeding the maximum of 3."

.. which also leads to a memory leak as xen_blkbk_remove never gets
called.
> 
> 
> > 
> > > 
> > >  drivers/block/xen-blkback/blkback.c | 386 ++++++++++---------
> > >  drivers/block/xen-blkback/common.h  |  78 ++--
> > >  drivers/block/xen-blkback/xenbus.c  | 359 ++++++++++++------
> > >  drivers/block/xen-blkfront.c        | 718 ++++++++++++++++++++++--------------
> > >  include/xen/interface/io/blkif.h    |  48 +++
> > >  5 files changed, 971 insertions(+), 618 deletions(-)
> > > 
> > > -- 
> > > 1.8.3.1
> > > 
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