Re: [PATCH v2 net-next 10/10] net: hns3: Add mqprio support when interacting with network stack

Hi, Yuval

On 2017/9/26 20:29, Yuval Mintz wrote:

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Hi, Yuval

On 2017/9/26 14:43, Yuval Mintz wrote:

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When using tc qdisc to configure DCB parameter, dcb_ops->setup_tc
is used to tell hclge_dcb module to do the setup.

While this might be a step in the right direction, this causes an inconsistency
in user experience - Some [well, most] vendors didn't allow the mqprio
priority mapping to affect DCB, instead relying on the dcbnl functionality
to control that configuration.

A couple of options to consider:
  - Perhaps said logic shouldn't be contained inside the driver but rather
     in mqprio logic itself. I.e., rely on DCBNL functionality [if available] from
     within mqprio and try changing the configuration.

In net/dcb/dcbnl.c
dcbnl_ieee_set already call dcbnl_ieee_notify to notify the user space
configuration has changed, does this dcbnl_ieee_notify function do the
job for us? I am not sure if lldpad has registered for this notifition.

Not that familiar with the dcbnl calls; Shouldn't dcbnl_setall be called to
make the configuration apply [or is that only for ieee]?

dcbnl_setall is for cee to make the configuration apply.
ieee does not have the apply operation.

Regardless, don't know if it makes sense to assume user-application would
fix the qdisc configuration by notification while dcbnl logic in kernel could have
done that instead.

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As you suggested below, can we add a new TC_MQPRIO_HW_OFFLOAD_
value to
reflect that the configuration is needed to be changed by dcbnl_ieee_set
(perhaps some other function) in dcbnl?
Do you think it is feasible?

Either I'm miseading your answer or we think of it from 2 opposite end.
I was thinking that the new offloaded flag would indicate to the underlying
driver that it's expected to offload the prio mapping [as part of DCB].
If the driver would be incapable of that it would refuse the offload.
User would then have to explicitly request that the qdisc offload.

Adding a new offloaded flag to indicate that mqpri is using a hardware offload
shared by dcbnl seems a good idea.
As I do not know how the idea go with other, I will drop the mqprio support in
this patch, and try to add the mqprio support as you suggested in the next
patchset.

Thanks again for the lengthly reply.

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  - Add a new TC_MQPRIO_HW_OFFLOAD_ value to explicitly reflect user
     request to allow this configuration to affect DCB.

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When using lldptool to configure DCB parameter, hclge_dcb module
call the client_ops->setup_tc to tell network stack which queue
and priority is using for specific tc.

You're basically bypassing the mqprio logic.
Since you're configuring the prio->queue mapping from DCB flow,
you'll get an mqprio-like behavior [meaning a transmitted packet
would reach a transmission queue associated with its priority] even
if device wasn't grated with an mqprio qdisc.
Why should your user even use mqprio? What benefit does he get from it?

...

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+static int hns3_nic_set_real_num_queue(struct net_device *netdev)
+{
+	struct hns3_nic_priv *priv = netdev_priv(netdev);
+	struct hnae3_handle *h = priv->ae_handle;
+	struct hnae3_knic_private_info *kinfo = &h->kinfo;
+	unsigned int queue_size = kinfo->rss_size * kinfo->num_tc;
+	int ret;
+
+	ret = netif_set_real_num_tx_queues(netdev, queue_size);
+	if (ret) {
+		netdev_err(netdev,
+			   "netif_set_real_num_tx_queues fail, ret=%d!\n",
+			   ret);
+		return ret;
+	}
+
+	ret = netif_set_real_num_rx_queues(netdev, queue_size);

I don't think you're changing the driver behavior, but why are you setting
the real number of rx queues based on the number of TCs?
Do you actually open (TC x RSS) Rx queues?

.