Date:   Mon, 25 Sep 2017 08:57:40 +0200
From:   Jiri Pirko <jiri@...nulli.us>
To:     Yunsheng Lin <linyunsheng@...wei.com>
Cc:     "davem@...emloft.net" <davem@...emloft.net>,
        huangdaode <huangdaode@...ilicon.com>,
        "xuwei (O)" <xuwei5@...ilicon.com>,
        "Liguozhu (Kenneth)" <liguozhu@...ilicon.com>,
        "Zhuangyuzeng (Yisen)" <yisen.zhuang@...wei.com>,
        Gabriele Paoloni <gabriele.paoloni@...wei.com>,
        John Garry <john.garry@...wei.com>,
        Linuxarm <linuxarm@...wei.com>,
        Salil Mehta <salil.mehta@...wei.com>,
        "lipeng (Y)" <lipeng321@...wei.com>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH net-next 10/10] net: hns3: Add mqprio support when
 interacting with network stack

Mon, Sep 25, 2017 at 02:45:08AM CEST, linyunsheng@...wei.com wrote:
>Hi, Jiri
>
>On 2017/9/24 19:37, Jiri Pirko wrote:
>> Sat, Sep 23, 2017 at 02:47:20AM CEST, linyunsheng@...wei.com wrote:
>>> Hi, Jiri
>>>
>>> On 2017/9/23 0:03, Jiri Pirko wrote:
>>>> Fri, Sep 22, 2017 at 04:11:51PM CEST, linyunsheng@...wei.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.
>> 
>> Okay. I understand that you have a usecase for mqprio mapping offload
>> without lldptool being involved. Ok. I believe it is wrong to call dcb_ops
>> from tc callback. You should have a generic layer inside the driver and
>> call it from both dcb_ops and tc callbacks.
>
>Actually, dcb_ops is our generic layer inside the driver.
>Below is high level architecture:
>
>       [ tc qdisc ]	       [ lldpad ]
>             |                     |
>             |                     |
>             |                     |
>       [ hns3_enet ]        [ hns3_dcbnl ]
>             \                    /
>                \              /
>                   \        /
>                 [ hclge_dcb ]
>                   /      \
>                /            \
>             /                  \
>     [ hclgc_main ]        [ hclge_tm ]
>
>hns3_enet.c implements the ndo_setup_tc callback.
>hns3_dcbnl.c implements the dcbnl_rtnl_ops for stack's DCBNL system.
>hclge_dcb implements the dcb_ops.
>So we already have a generic layer that tc and dcbnl all call from.
>
>> 
>> Also, what happens If I run lldptool concurrently with mqprio? Who wins
>> and is going to configure the mapping?
>
>Both lldptool and tc qdisc cmd use rtnl interface provided by stack, so
>they are both protected by rtnl_lock, so we do not have to do the locking
>in the driver.

I was not asking about locking, which is obvious, I was asking about the
behaviour. Like for example:
If I use tc to configure some mapping, later on I run lldptool and change
the mapping. Does the tc dump show the updated values or the original
ones?

>
>The locking is in rtnetlink_rcv_msg:
>
>	rtnl_lock();
>	handlers = rtnl_dereference(rtnl_msg_handlers[family]);
>	if (handlers) {
>		doit = READ_ONCE(handlers[type].doit);
>		if (doit)
>			err = doit(skb, nlh, extack);
>	}
>	rtnl_unlock();
>
>Thanks.
>
>> 
>> 
>>>
>>>>
>>>>
>>>>
>>>>> I hope I did not misunderstand your question, thanks
>>>>> for your time reviewing.
>>>>
>>>> .
>>>>
>>>
>> 
>> .
>> 
>

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