linux-kernel - Re: [PATCH net-next 0/2] Add mqprio hardware offload support in hns3 driver

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Date:   Fri, 13 Oct 2017 10:07:49 +0800
From:   Yunsheng Lin <linyunsheng@...wei.com>
To:     Yuval Mintz <yuvalm@...lanox.com>,
        "davem@...emloft.net" <davem@...emloft.net>
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>
Subject: Re: [PATCH net-next 0/2] Add mqprio hardware offload support in hns3
 driver

Hi, Yuval

On 2017/10/13 4:21, Yuval Mintz wrote:
>> This patchset adds a new hardware offload type in mqprio before adding
>> mqprio hardware offload support in hns3 driver.
> 
> I think one of the biggest issues in tying this to DCB configuration is the
> non-immediate [and possibly non persistent] configuration.
> 
> Scenario #1:
> User is configuring mqprio offloaded with 3 TCs while device is in willing mode.
> Would you expect the driver to immediately respond with a success or instead
> delay the return until the DCBx negotiation is complete and the operational
> num of TCs is actually 3?

Well, when user requsts the mqprio offloaded by a hardware shared by DCB, I expect
the user is not using the dcb tool.
If user is still using dcb tool, then result is undefined.

The scenario you mention maybe can be enforced by setting willing to zero when user
is requesting the mqprio offload, and restore the willing bit when unloaded the mqprio
offload.
But I think the real issue is that dcb and mqprio shares the tc system in the stack,
the problem may be better to be fixed in the stack rather than in the driver, as you
suggested in the DCB patchset. What do you think?

> 
> Scenario #2:
> Assume user explicitly offloaded mqprio with 3 TCs, but now DCB configuration
> has changed on the peer side and 4 TCs is the new negotiated operational value.
> Your current driver logic would change the number of TCs underneath the user
> configuration [and it would actually probably work due to mqprio being a crappy
> qdisc]. But was that the user actual intention?
> [I think the likely answer in this scenario is 'yes' since the alternative is no better.
> But I still thought it was worth mentioning]

You are right, the problem also have something to do with mqprio and dcb sharing
the tc in the stack.

Druing testing, when user explicitly offloaded mqprio with 3 TCs, all
queue has a default pfifo mqprio attached, after DCB changes the tc num to 4,
using tc qdisc shows some queue does not have a default pfifo mqprio attached.

Maybe we can add a callback to notify mqprio the configuration has changed.

Thanks
Yunsheng Lin

> 
> Cheers,
> Yuval
> 
>>
>> Yunsheng Lin (2):
>>   mqprio: Add a new hardware offload type in mqprio
>>   net: hns3: Add mqprio hardware offload support in hns3 driver
>>
>>  drivers/net/ethernet/hisilicon/hns3/hnae3.h        |  1 +
>>  .../net/ethernet/hisilicon/hns3/hns3pf/hclge_dcb.c | 23 +++++++++++
>>  .../net/ethernet/hisilicon/hns3/hns3pf/hns3_enet.c | 46 ++++++++++++++-
>> -------
>>  include/uapi/linux/pkt_sched.h                     |  1 +
>>  4 files changed, 55 insertions(+), 16 deletions(-)
>>
>> --
>> 1.9.1
> 
> 
>