linux-kernel - Re: [PATCH 6/6] drivers: enable xenwatch multithreading for xen-netback and xen-blkback driver

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Message-ID: <20180914093858.fwu6aqwwjbsdbbt4@zion.uk.xensource.com>
Date:   Fri, 14 Sep 2018 10:38:58 +0100
From:   Wei Liu <wei.liu2@...rix.com>
To:     Juergen Gross <jgross@...e.com>
CC:     Dongli Zhang <dongli.zhang@...cle.com>,
        <xen-devel@...ts.xenproject.org>, <linux-kernel@...r.kernel.org>,
        <boris.ostrovsky@...cle.com>, <paul.durrant@...rix.com>,
        <wei.liu2@...rix.com>, <konrad.wilk@...cle.com>,
        <roger.pau@...rix.com>, <srinivas.eeda@...cle.com>
Subject: Re: [PATCH 6/6] drivers: enable xenwatch multithreading for
 xen-netback and xen-blkback driver

On Fri, Sep 14, 2018 at 11:16:30AM +0200, Juergen Gross wrote:
> On 14/09/18 09:34, Dongli Zhang wrote:
> > This is the 6th patch of a (6-patch) patch set.
> > 
> > As the 'use_mtwatch' for xen-netback and xen-blkback are set to true,
> > probing any xenbus devices of those two drivers would create the per-domU
> > xenwatch thread for the domid the new devices belong to, or increment the
> > reference count  of existing thread.
> > 
> > Xenwatch multithreading might be enabled for more xen backend pv drivers in
> > the future.
> > 
> > Signed-off-by: Dongli Zhang <dongli.zhang@...cle.com>
> > ---
> >  drivers/block/xen-blkback/xenbus.c | 3 ++-
> >  drivers/net/xen-netback/xenbus.c   | 1 +
> >  2 files changed, 3 insertions(+), 1 deletion(-)
> > 
> > diff --git a/drivers/block/xen-blkback/xenbus.c b/drivers/block/xen-blkback/xenbus.c
> > index a4bc74e..debbbd0 100644
> > --- a/drivers/block/xen-blkback/xenbus.c
> > +++ b/drivers/block/xen-blkback/xenbus.c
> > @@ -1108,7 +1108,8 @@ static struct xenbus_driver xen_blkbk_driver = {
> >  	.ids  = xen_blkbk_ids,
> >  	.probe = xen_blkbk_probe,
> >  	.remove = xen_blkbk_remove,
> > -	.otherend_changed = frontend_changed
> > +	.otherend_changed = frontend_changed,
> > +	.use_mtwatch = true,
> >  };
> >  
> >  int xen_blkif_xenbus_init(void)
> > diff --git a/drivers/net/xen-netback/xenbus.c b/drivers/net/xen-netback/xenbus.c
> > index cd51492..63d46a7 100644
> > --- a/drivers/net/xen-netback/xenbus.c
> > +++ b/drivers/net/xen-netback/xenbus.c
> > @@ -1203,6 +1203,7 @@ static struct xenbus_driver netback_driver = {
> >  	.remove = netback_remove,
> >  	.uevent = netback_uevent,
> >  	.otherend_changed = frontend_changed,
> > +	.use_mtwatch = true,
> 
> Is there a special reason why kernel based backends shouldn't all use
> the multithread model? This would avoid the need for the use_mtwatch
> struct member.
> 
> This is meant as an honest question. I'm really not sure we should
> switch all backends at once. OTOH I can't see any real downsides.
> 
> Thoughts?

I don't see any downside.

Wei.

> 
> 
> Juergen