Subject: Re: [Xen-devel] [PATCH V3 1/2] xen-netback: limit xen vif max queues number to online cpus

From: Andrew Cooper <[email-masked]>
Date: Fri, 23 Oct 2015 10:51:59 +0100

On 23/10/15 10:44, Joe Jin wrote:
> Should not allocate xen vif queues number more than online cpus.
>
> Signed-off-by: Joe Jin <[email-masked]>
> Cc: Jan Beulich <[email-masked]>
> Cc: Wei Liu <[email-masked]>
> Cc: Ian Campbell <[email-masked]>
> Cc: Boris Ostrovsky <[email-masked]>
> Cc: Konrad Rzeszutek Wilk <[email-masked]>
> ---
>  drivers/net/xen-netback/netback.c |   28 ++++++++++++++++++++++------
>  1 files changed, 22 insertions(+), 6 deletions(-)
>
> diff --git a/drivers/net/xen-netback/netback.c b/drivers/net/xen-netback/netback.c
> index ec98d43..021dcb0 100644
> --- a/drivers/net/xen-netback/netback.c
> +++ b/drivers/net/xen-netback/netback.c
> @@ -68,7 +68,9 @@ unsigned int rx_stall_timeout_msecs = 60000;
>  module_param(rx_stall_timeout_msecs, uint, 0444);
>  
>  unsigned int xenvif_max_queues;
> -module_param_named(max_queues, xenvif_max_queues, uint, 0644);
> +static int xennet_set_max_queues(const char *val, struct kernel_param *kp);
> +module_param_call(max_queues, xennet_set_max_queues, param_get_uint,
> +		  &xenvif_max_queues, 0644);
>  MODULE_PARM_DESC(max_queues,
>  		 "Maximum number of queues per virtual interface");
>  
> @@ -107,6 +109,20 @@ static struct xen_netif_rx_response *make_rx_response(struct xenvif_queue *queue
>  					     u16      size,
>  					     u16      flags);
>  
> +static int xennet_set_max_queues(const char *val, struct kernel_param *kp)
> +{
> +	unsigned int cpus = num_online_cpus();

This calculation is problematic in the scenario where a guest boots up,
then has more cpus hotplugged in, then wants to set up a sensible number
of queues.

~Andrew