Subject: Re: [net-next-2.6 PATCH v6 2/2] net_sched: implement a root container qdisc sch_mqprio

From: Jarek Poplawski <[email-masked]>
Date: Fri, 7 Jan 2011 22:21:40 +0100

On Thu, Jan 06, 2011 at 07:12:16PM -0800, John Fastabend wrote:
> This implements a mqprio queueing discipline that by default creates
> a pfifo_fast qdisc per tx queue and provides the needed configuration
> interface.
> 
> Using the mqprio qdisc the number of tcs currently in use along
> with the range of queues alloted to each class can be configured. By
> default skbs are mapped to traffic classes using the skb priority.
> This mapping is configurable.
> 
> Configurable parameters,
> 
> struct tc_mqprio_qopt {
>         __u8    num_tc;
>         __u8    prio_tc_map[TC_BITMASK + 1];
>         __u8    hw;
>         __u16   count[TC_MAX_QUEUE];
>         __u16   offset[TC_MAX_QUEUE];
> };
> 
> Here the count/offset pairing give the queue alignment and the
> prio_tc_map gives the mapping from skb->priority to tc.
> 
> The hw bit determines if the hardware should configure the count
> and offset values. If the hardware bit is set then the operation
> will fail if the hardware does not implement the ndo_setup_tc
> operation. This is to avoid undetermined states where the hardware
> may or may not control the queue mapping. Also minimal bounds
> checking is done on the count/offset to verify a queue does not
> exceed num_tx_queues and that queue ranges do not overlap. Otherwise
> it is left to user policy or hardware configuration to create
> useful mappings.
> 
> It is expected that hardware QOS schemes can be implemented by
> creating appropriate mappings of queues in ndo_tc_setup().
> 
> One expected use case is drivers will use the ndo_setup_tc to map
> queue ranges onto 802.1Q traffic classes. This provides a generic
> mechanism to map network traffic onto these traffic classes and
> removes the need for lower layer drivers to know specifics about
> traffic types.
> 
> Signed-off-by: John Fastabend <[email-masked]>
> ---
> 
>  include/linux/pkt_sched.h |   12 +
>  net/sched/Kconfig         |   12 +
>  net/sched/Makefile        |    1 
>  net/sched/sch_generic.c   |    4 
>  net/sched/sch_mqprio.c    |  415 +++++++++++++++++++++++++++++++++++++++++++++
>  5 files changed, 444 insertions(+), 0 deletions(-)
>  create mode 100644 net/sched/sch_mqprio.c
> 
> diff --git a/include/linux/pkt_sched.h b/include/linux/pkt_sched.h
> index 2cfa4bc..776cd93 100644
> --- a/include/linux/pkt_sched.h
> +++ b/include/linux/pkt_sched.h
> @@ -481,4 +481,16 @@ struct tc_drr_stats {
>  	__u32	deficit;
>  };
>  
> +/* MQPRIO */
> +#define TC_QOPT_BITMASK 15
> +#define TC_QOPT_MAX_QUEUE 16
> +
> +struct tc_mqprio_qopt {
> +	__u8	num_tc;
> +	__u8	prio_tc_map[TC_QOPT_BITMASK + 1];
> +	__u8	hw;
> +	__u16	count[TC_QOPT_MAX_QUEUE];
> +	__u16	offset[TC_QOPT_MAX_QUEUE];
> +};

...
> +static int mqprio_parse_opt(struct net_device *dev, struct tc_mqprio_qopt *qopt)
> +{
> +	int i, j;
> +
> +	/* Verify num_tc is not out of max range */
> +	if (qopt->num_tc > TC_QOPT_MAX_QUEUE)

If these TC_QOPTs really couldn't be avoided you should probably check
them with BUILD_BUG_ON() but use only TC_MAX_QUEUE/TC_BITMASK
everywhere. Otherwise, it looks OK to me.

Jarek P.