netdev - Re: [next-queue PATCH 2/3] net/sched: Introduce Credit Based Shaper (CBS) qdisc

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Date:   Wed, 27 Sep 2017 14:14:52 -0700
From:   Vinicius Costa Gomes <vinicius.gomes@...el.com>
To:     Cong Wang <xiyou.wangcong@...il.com>
Cc:     Linux Kernel Network Developers <netdev@...r.kernel.org>,
        intel-wired-lan <intel-wired-lan@...ts.osuosl.org>,
        Jamal Hadi Salim <jhs@...atatu.com>,
        Jiri Pirko <jiri@...nulli.us>, andre.guedes@...el.com,
        ivan.briano@...el.com, jesus.sanchez-palencia@...el.com,
        boon.leong.ong@...el.com, richardcochran@...il.com,
        henrik@...tad.us
Subject: Re: [next-queue PATCH 2/3] net/sched: Introduce Credit Based Shaper (CBS) qdisc

Hi,

Cong Wang <xiyou.wangcong@...il.com> writes:

> On Tue, Sep 26, 2017 at 4:39 PM, Vinicius Costa Gomes
> <vinicius.gomes@...el.com> wrote:
>> +static int cbs_init(struct Qdisc *sch, struct nlattr *opt)
>> +{
>> +       struct cbs_sched_data *q = qdisc_priv(sch);
>> +       struct net_device *dev = qdisc_dev(sch);
>> +
>> +       if (!opt)
>> +               return -EINVAL;
>> +
>> +       /* FIXME: this means that we can only install this qdisc
>> +        * "under" mqprio. Do we need a more generic way to retrieve
>> +        * the queue, or do we pass the netdev_queue to the driver?
>> +        */
>> +       q->queue = TC_H_MIN(sch->parent) - 1 - netdev_get_num_tc(dev);
>> +
>> +       return cbs_change(sch, opt);
>> +}
>
> Yeah it is ugly to assume its parent is mqprio, at least you should
> error out if it is not the case.

Will add an error for this, for now.

>
> I am not sure how we can solve this elegantly, perhaps you should
> extend mqprio rather than add a new one?

Is the alternative hinted in the FIXME worse? Instead of passing the
index of the hardware queue to the driver we pass the pointer to a
netdev_queue to the driver and it "discovers" the HW queue from that.


Cheers,
--
Vinicius