netdev - RE: [PATCH net-next 0/2] Add mqprio hardware offload support in hns3 driver

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Date:   Thu, 12 Oct 2017 20:21:04 +0000
From:   Yuval Mintz <yuvalm@...lanox.com>
To:     Yunsheng Lin <linyunsheng@...wei.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>,
        "yisen.zhuang@...wei.com" <yisen.zhuang@...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

> 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?

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]

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