Re: [PATCH net-next 1/3] net: sched: update default qdisc visibility after Tx queue cnt changes

On Wed, 15 Sep 2021 09:31:08 -0700 Cong Wang wrote:

On Mon, Sep 13, 2021 at 3:53 PM Jakub Kicinski [off-list ref] wrote:

quoted

diff --git a/net/core/dev.c b/net/core/dev.c
index 74fd402d26dd..f930329f0dc2 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c

@@ -2921,6 +2921,8 @@ int netif_set_real_num_tx_queues(struct net_device *dev, unsigned int txq)
                if (dev->num_tc)
                        netif_setup_tc(dev, txq);

+               dev_qdisc_change_real_num_tx(dev, txq);
+  

Don't we need to flip the device with dev_deactivate()+dev_activate()?
It looks like the only thing this function resets is qdisc itself, and only
partially.

We're only making the qdiscs visible, there should be 
no datapath-visible change.

quoted

                dev->real_num_tx_queues = txq;

                if (disabling) {

quoted

diff --git a/net/sched/sch_mq.c b/net/sched/sch_mq.c
index e79f1afe0cfd..db18d8a860f9 100644
--- a/net/sched/sch_mq.c
+++ b/net/sched/sch_mq.c

@@ -125,6 +125,29 @@ static void mq_attach(struct Qdisc *sch)
        priv->qdiscs = NULL;
 }

+static void mq_change_real_num_tx(struct Qdisc *sch, unsigned int new_real_tx)  

This is nearly identical to mqprio_change_real_num_tx(), can we reuse
it?

Indeed, I was a little unsure where best to place the helper.
Since mq is always built if mqprio is my instinct would be to
export mq_change_real_num_tx and use it in mqprio. But I didn't 
see any existing exports (mq_attach(), mq_queue_get() are also
identical and are not shared) so I just copy&pasted the logic.

LMK if (a) that's fine; (b) I should share the new code; 
(c) I should post a patch to share all the code that's identical;...