Re: [PATCH v3 net-next] net: vlan: Use vlan_prio instead of vlan_qos in mapping
From: Yajun Deng
Date: Sun Oct 20 2024 - 22:23:28 EST
October 20, 2024 at 8:29 PM, "Ido Schimmel" <idosch@xxxxxxxxxx> wrote:
>
> On Fri, Oct 18, 2024 at 10:12:33PM +0800, Yajun Deng wrote:
>
> >
> > The vlan_qos member is used to save the vlan qos, but we only save the
> >
> > priority. Also, we will get the priority in vlan netlink and proc.
> >
> > We can just save the vlan priority using vlan_prio, so we can use vlan_prio
> >
> > to get the priority directly.
> >
> >
> >
> > For flexibility, we introduced vlan_dev_get_egress_priority() helper
> >
> > function. After this patch, we will call vlan_dev_get_egress_priority()
> >
> > instead of vlan_dev_get_egress_qos_mask() in irdma.ko and rdma_cm.ko.
> >
> > Because we don't need the shift and mask operations anymore.
> >
> >
> >
> > There is no functional changes.
> >
>
> Not sure I understand the motivation.
>
> IIUC, currently, struct vlan_priority_tci_mapping::vlan_qos is shifted
>
> and masked in the control path (vlan_dev_set_egress_priority) so that
>
> these calculations would not need to be performed in the data path where
>
> the VLAN header is constructed (vlan_dev_hard_header /
>
> vlan_dev_hard_start_xmit).
>
> This patch seems to move these calculations to the data path so that
>
> they would not need to be performed in the control path when dumping the
>
> priority mapping via netlink / proc.
>
Yes, you're right about that. But there's another case.
Not all callers need to get the vlan qos, but some callers need to get the
vlan priority (get_vlan_ndev_tc/irdma_iw_get_vlan_prio/irdma_roce_get_vlan_prio)
in irdma.ko and rdma_cm.ko.
These callers and vlan_dev_set_egress_priority are opposite operations.
If we use vlan_prio, we can save these two opposite operations.
> Why is it a good trade-off?
>