netdev - Re: [PATCH net] xen-netback: respect user provided max

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Date:	Wed, 9 Sep 2015 11:16:28 +0100
From:	Wei Liu <wei.liu2@...rix.com>
To:	David Vrabel <david.vrabel@...rix.com>
CC:	Wei Liu <wei.liu2@...rix.com>,
	Xen-devel <xen-devel@...ts.xenproject.org>,
	<netdev@...r.kernel.org>, Ian Campbell <ian.campbell@...rix.com>,
	"Johnny Strom" <johnny.strom@...uxsolutions.fi>
Subject: Re: [PATCH net] xen-netback: respect user provided max_queues

On Wed, Sep 09, 2015 at 11:12:44AM +0100, David Vrabel wrote:
> On 09/09/15 11:09, Wei Liu wrote:
> > Originally that parameter was always reset to num_online_cpus during
> > module initialisation, which renders it useless.
> > 
> > The fix is to only set max_queues to num_online_cpus when user has not
> > provided a value.
> [...]
> > --- a/drivers/net/xen-netback/netback.c
> > +++ b/drivers/net/xen-netback/netback.c
> > @@ -67,7 +67,7 @@ module_param(rx_drain_timeout_msecs, uint, 0444);
> >  unsigned int rx_stall_timeout_msecs = 60000;
> >  module_param(rx_stall_timeout_msecs, uint, 0444);
> >  
> > -unsigned int xenvif_max_queues;
> > +unsigned int xenvif_max_queues = 0;
> 
> You don't need this.
> 
> Otherwise,
> 
> Reviewed-by: David Vrabel <david.vrabel@...rix.com>
> 
> Is an equivalent fix needed in netfront?
> 

I think so.

I will address your comment and send both fixes (front and back) in a
series.

Wei.

> David
> 
> >  module_param_named(max_queues, xenvif_max_queues, uint, 0644);
> >  MODULE_PARM_DESC(max_queues,
> >  		 "Maximum number of queues per virtual interface");
> > @@ -2105,8 +2105,11 @@ static int __init netback_init(void)
> >  	if (!xen_domain())
> >  		return -ENODEV;
> >  
> > -	/* Allow as many queues as there are CPUs, by default */
> > -	xenvif_max_queues = num_online_cpus();
> > +	/* Allow as many queues as there are CPUs if user has not
> > +	 * specified a value.
> > +	 */
> > +	if (xenvif_max_queues == 0)
> > +		xenvif_max_queues = num_online_cpus();
> >  
> >  	if (fatal_skb_slots < XEN_NETBK_LEGACY_SLOTS_MAX) {
> >  		pr_info("fatal_skb_slots too small (%d), bump it to XEN_NETBK_LEGACY_SLOTS_MAX (%d)\n",
> > 
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