netdev - Re: [PATCH V7 net-next 0/6] ethtool: add support to set/get tx copybreak buf size and rx buf len

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Date:   Thu, 27 Oct 2022 12:03:07 +0300
From:   Gal Pressman <gal@...dia.com>
To:     Yunsheng Lin <linyunsheng@...wei.com>,
        Guangbin Huang <huangguangbin2@...wei.com>,
        davem@...emloft.net, kuba@...nel.org, mkubecek@...e.cz,
        andrew@...n.ch, amitc@...lanox.com, idosch@...sch.org,
        danieller@...dia.com, jesse.brandeburg@...el.com,
        anthony.l.nguyen@...el.com, jdike@...toit.com, richard@....at,
        anton.ivanov@...bridgegreys.com, netanel@...zon.com,
        akiyano@...zon.com, gtzalik@...zon.com, saeedb@...zon.com,
        chris.snook@...il.com, ulli.kroll@...glemail.com,
        linus.walleij@...aro.org, jeroendb@...gle.com, csully@...gle.com,
        awogbemila@...gle.com, jdmason@...zu.us, rain.1986.08.12@...il.com,
        zyjzyj2000@...il.com, kys@...rosoft.com, haiyangz@...rosoft.com,
        mst@...hat.com, jasowang@...hat.com, doshir@...are.com,
        pv-drivers@...are.com, jwi@...ux.ibm.com, kgraul@...ux.ibm.com,
        hca@...ux.ibm.com, gor@...ux.ibm.com, johannes@...solutions.net
Cc:     netdev@...r.kernel.org, lipeng321@...wei.com,
        chenhao288@...ilicon.com, linux-s390@...r.kernel.org
Subject: Re: [PATCH V7 net-next 0/6] ethtool: add support to set/get tx
 copybreak buf size and rx buf len

On 27/10/2022 03:49, Yunsheng Lin wrote:
> On 2022/10/26 22:00, Gal Pressman wrote:
>> On 18/11/2021 14:12, Guangbin Huang wrote:
>>> From: Hao Chen <chenhao288@...ilicon.com>
>>>
>>> This series add support to set/get tx copybreak buf size and rx buf len via
>>> ethtool and hns3 driver implements them.
>>>
>>> Tx copybreak buf size is used for tx copybreak feature which for small size
>>> packet or frag. Use ethtool --get-tunable command to get it, and ethtool
>>> --set-tunable command to set it, examples are as follow:
>>>
>>> 1. set tx spare buf size to 102400:
>>> $ ethtool --set-tunable eth1 tx-buf-size 102400
>>>
>>> 2. get tx spare buf size:
>>> $ ethtool --get-tunable eth1 tx-buf-size
>>> tx-buf-size: 102400
>> Hi Guangbin,
>> Can you please clarify the difference between TX copybreak and TX
>> copybreak buf size?
> Hi Gal,
> 'TX copybreak buf size' is the size of buffer allocated to a queue
> in order to support copybreak handling when skb->len <= 'TX copybreak',
>
> see hns3_can_use_tx_bounce() for 'TX copybreak' and
> hns3_init_tx_spare_buffer() for 'TX copybreak buf size'.

Thanks Yunsheng!
IIUC, there's a single buffer per TX queue, not per TX packet, correct?

One way to implement TX copybreak is using an inline WQE, where the WQE
itself serves as the bounce buffer, sounds like 'TX copybreak buf size'
cannot be used in such case?