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

[Yunsheng Lin <linyunsheng@huawei.com>]

Hi, Jiri

On 2017/9/23 0:03, Jiri Pirko wrote:
> Fri, Sep 22, 2017 at 04:11:51PM CEST, linyunsheng@huawei.com wrote:
>> Hi, Jiri
>>
>>>> - if (!tc) {
>>>> + if (if_running) {
>>>> + (void)hns3_nic_net_stop(netdev);
>>>> + msleep(100);
>>>> + }
>>>> +
>>>> + ret = (kinfo->dcb_ops && kinfo->dcb_ops->>setup_tc) ?
>>>> + kinfo->dcb_ops->setup_tc(h, tc, prio_tc) : ->EOPNOTSUPP;
>>
>>> This is most odd. Why do you call dcb_ops from >ndo_setup_tc callback?
>>> Why are you mixing this together? prio->tc mapping >can be done
>>> directly in dcbnl
>>
>> Here is what we do in dcb_ops->setup_tc:
>> Firstly, if current tc num is different from the tc num
>> that user provide, then we setup the queues for each
>> tc.
>>
>> Secondly, we tell hardware the pri to tc mapping that
>> the stack is using. In rx direction, our hardware need
>> that mapping to put different packet into different tc'
>> queues according to the priority of the packet, then
>> rss decides which specific queue in the tc should the
>> packet goto.
>>
>> By mixing, I suppose you meant why we need the
>> pri to tc infomation?
> 
> by mixing, I mean what I wrote. You are calling dcb_ops callback from
> ndo_setup_tc callback. So you are mixing DCBNL subsystem and TC
> subsystem. Why? Why do you need sch_mqprio? Why DCBNL is not enough for
> all?

When using lldptool, dcbnl is involved.

But when using tc qdisc, dcbbl is not involved, below is the a few key
call graph in the kernel when tc qdisc cmd is executed.

cmd:
tc qdisc add dev eth0 root handle 1:0 mqprio num_tc 4 map 1 2 3 3 1 3 1 1 hw 1

call graph:
rtnetlink_rcv_msg -> tc_modify_qdisc -> qdisc_create -> mqprio_init ->
hns3_nic_setup_tc

When hns3_nic_setup_tc is called, we need to know how many tc num and
prio_tc mapping from the tc_mqprio_qopt which is provided in the paramter
in the ndo_setup_tc function, and dcb_ops is the our hardware specific
method to setup the tc related parameter to the hardware, so this is why
we call dcb_ops callback in ndo_setup_tc callback.

I hope this will answer your question, thanks for your time.

> 
> 
> 
>> I hope I did not misunderstand your question, thanks
>> for your time reviewing.
> 
> .
>