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

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Message-ID: <AM0PR0502MB3683FFF227DA3D136AA63987BF7B0@AM0PR0502MB3683.eurprd05.prod.outlook.com>
Date:   Tue, 26 Sep 2017 12:29:02 +0000
From:   Yuval Mintz <yuvalm@...lanox.com>
To:     Yunsheng Lin <linyunsheng@...wei.com>
CC:     "huangdaode@...ilicon.com" <huangdaode@...ilicon.com>,
        "xuwei5@...ilicon.com" <xuwei5@...ilicon.com>,
        "liguozhu@...ilicon.com" <liguozhu@...ilicon.com>,
        "Yisen.Zhuang@...wei.com" <Yisen.Zhuang@...wei.com>,
        "gabriele.paoloni@...wei.com" <gabriele.paoloni@...wei.com>,
        "john.garry@...wei.com" <john.garry@...wei.com>,
        "linuxarm@...wei.com" <linuxarm@...wei.com>,
        "salil.mehta@...wei.com" <salil.mehta@...wei.com>,
        "lipeng321@...wei.com" <lipeng321@...wei.com>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "davem@...emloft.net" <davem@...emloft.net>
Subject: RE: [PATCH v2 net-next 10/10] net: hns3: Add mqprio support when
 interacting with network stack

> Hi, Yuval
> 
> On 2017/9/26 14:43, Yuval Mintz wrote:
> >> 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]?
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.

> 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.

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