netdev - Re: [net-next-2.6 PATCH 2/4] net_sched: Allow multiple mq qdisc to be used as non-root

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Date:	Tue, 21 Dec 2010 11:21:21 -0800
From:	John Fastabend <john.r.fastabend@...el.com>
To:	Ben Hutchings <bhutchings@...arflare.com>
CC:	"davem@...emloft.net" <davem@...emloft.net>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	"hadi@...erus.ca" <hadi@...erus.ca>,
	"shemminger@...tta.com" <shemminger@...tta.com>,
	"tgraf@...radead.org" <tgraf@...radead.org>,
	"eric.dumazet@...il.com" <eric.dumazet@...il.com>,
	"nhorman@...driver.com" <nhorman@...driver.com>
Subject: Re: [net-next-2.6 PATCH 2/4] net_sched: Allow multiple mq qdisc to
 be used as non-root

On 12/20/2010 3:12 PM, Ben Hutchings wrote:
> On Fri, 2010-12-17 at 07:34 -0800, John Fastabend wrote:
> [...]
>> diff --git a/net/sched/sch_mq.c b/net/sched/sch_mq.c
>> index ecc302f..35ed26d 100644
>> --- a/net/sched/sch_mq.c
>> +++ b/net/sched/sch_mq.c
>> @@ -19,17 +19,39 @@
>>  
>>  struct mq_sched {
>>  	struct Qdisc		**qdiscs;
>> +	u8 num_tc;
>>  };
>>  
>> +static void mq_queues(struct net_device *dev, struct Qdisc *sch,
>> +		      unsigned int *count, unsigned int *offset)
>> +{
>> +	struct mq_sched *priv = qdisc_priv(sch);
>> +	if (priv->num_tc) {
>> +		int queue = TC_H_MIN(sch->parent) - 1;
>> +		if (count)
>> +			*count = dev->tc_to_txq[queue].count;
>> +		if (offset)
>> +			*offset = dev->tc_to_txq[queue].offset;
>> +	} else {
>> +		if (count)
>> +			*count = dev->num_tx_queues;
>> +		if (offset)
>> +			*offset = 0;
>> +	}
>> +}
> [...]
> 
> It looks like num_tc will be set even for the root qdisc if the device
> is capable of QoS.  Would mq_queues() behave correctly then, i.e. is the
> queue range for priority 0 required to be [0, dev->num_tx_queues)?

If num_tc is set the mclass qdisc is loaded by default and not the mq qdisc. When mclass is destroyed it sets num_tc to zero. So I believe mq_queues() will behave correctly ie if mq is the root qdisc [0, dev->num_tx_queues) will be used.

> 
> Also it would be neater to return count and offset together as struct
> netdev_tc_txq, rather than through optional out-parameters.  Even better
> would be to cache these in struct mq_sched, if that's possible.
> 

Yes should be possible to embed this in mq_sched.

> Ben.
> 

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