netdev - Re: [PATCH net 5/6] net/sched: Refactor qdisc_graft() for ingress and clsact Qdiscs

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Date: Mon, 8 May 2023 15:24:22 -0700
From: Peilin Ye <yepeilin.cs@...il.com>
To: Jamal Hadi Salim <jhs@...atatu.com>
Cc: "David S. Miller" <davem@...emloft.net>,
	Eric Dumazet <edumazet@...gle.com>,
	Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>,
	Cong Wang <xiyou.wangcong@...il.com>, Jiri Pirko <jiri@...nulli.us>,
	Peilin Ye <peilin.ye@...edance.com>,
	Daniel Borkmann <daniel@...earbox.net>,
	Vlad Buslov <vladbu@...lanox.com>,
	Pedro Tammela <pctammela@...atatu.com>,
	Hillf Danton <hdanton@...a.com>, netdev@...r.kernel.org,
	linux-kernel@...r.kernel.org, Cong Wang <cong.wang@...edance.com>,
	John Fastabend <john.fastabend@...il.com>
Subject: Re: [PATCH net 5/6] net/sched: Refactor qdisc_graft() for ingress
 and clsact Qdiscs

On Mon, May 08, 2023 at 07:29:26AM -0400, Jamal Hadi Salim wrote:
> On Fri, May 5, 2023 at 8:15 PM Peilin Ye <yepeilin.cs@...il.com> wrote:
> >
> > Grafting ingress and clsact Qdiscs does not need a for-loop in
> > qdisc_graft().  Refactor it.  No functional changes intended.
> 
> This one i am not so sure;  num_q = 1 implies it will run on the for
> loop only once. I am not sure it improves readability either. Anyways
> for the effort you put into it i am tossing a coin and saying:
> Reviewed-by: Jamal Hadi Salim <jhs@...atatu.com>
> Acked-by: Jamal Hadi Salim <jhs@...atatu.com>

Yeah, it doesn't make much difference itself.  I'm just afraid that,
without [5/6], [6/6] would look like:

		for (i = 0; i < num_q; i++) {
			if (!ingress) {
				dev_queue = netdev_get_tx_queue(dev, i);
				old = dev_graft_qdisc(dev_queue, new);
			else {
				old = dev_graft_qdisc(dev_queue, NULL);
			}

			if (new && i > 0)
				qdisc_refcount_inc(new);

			if (!ingress) {
				qdisc_put(old);
			} else {
                                /* {ingress,clsact}_destroy() "old" before grafting "new" to avoid
                                 * unprotected concurrent accesses to net_device::miniq_{in,e}gress
                                 * pointer(s) in mini_qdisc_pair_swap().
                                 */
				qdisc_notify(net, skb, n, classid, old, new, extack);
				qdisc_destroy(old);
			}

			if (ingress)
				dev_graft_qdisc(dev_queue, new);
		}

The "!ingress" path doesn't share a single line with "ingress", which
looks a bit weird to me.  Personally I'd like to keep [5/6].

Thanks,
Peilin Ye