netdev - Re: [PATCH net-next v3 2/4] sch_htb: Hierarchical QoS hardware offload

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Message-ID: <20201221171736.6f5ebe1d@kicinski-fedora-pc1c0hjn.dhcp.thefacebook.com>
Date:   Mon, 21 Dec 2020 17:17:36 -0800
From:   Jakub Kicinski <kuba@...nel.org>
To:     Maxim Mikityanskiy <maximmi@...lanox.com>
Cc:     "David S. Miller" <davem@...emloft.net>,
        Jamal Hadi Salim <jhs@...atatu.com>,
        Cong Wang <xiyou.wangcong@...il.com>,
        Jiri Pirko <jiri@...nulli.us>, David Ahern <dsahern@...il.com>,
        Saeed Mahameed <saeedm@...dia.com>,
        Tariq Toukan <tariqt@...dia.com>,
        Yossi Kuperman <yossiku@...dia.com>,
        Maxim Mikityanskiy <maximmi@...dia.com>,
        Dan Carpenter <dan.carpenter@...cle.com>,
        netdev@...r.kernel.org
Subject: Re: [PATCH net-next v3 2/4] sch_htb: Hierarchical QoS hardware
 offload

On Tue, 15 Dec 2020 09:42:11 +0200 Maxim Mikityanskiy wrote:
> +	q->offload = nla_get_flag(tb[TCA_HTB_OFFLOAD]);
> +
> +	if (q->offload) {
> +		if (!tc_can_offload(dev) || !dev->netdev_ops->ndo_setup_tc)
> +			return -EOPNOTSUPP;

Is there a check somewhere making sure this is the root?

> +		q->num_direct_qdiscs = dev->real_num_tx_queues;

Why real_num_tx_queues? How do you handle queue count changes?

> +		q->direct_qdiscs = kcalloc(q->num_direct_qdiscs,
> +					   sizeof(*q->direct_qdiscs),
> +					   GFP_KERNEL);
> +		if (!q->direct_qdiscs)
> +			return -ENOMEM;
> +	}

I can't quite parse after 20 minutes of staring at this code what the
relationship between the device queues and classes is. Is there any
relationship between real_num_tx_queues and classes?