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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Message-ID: <0cf97cc1-1a99-21f6-93ef-e8c2f4c6f03c@huawei.com>
Date:   Fri, 28 Oct 2022 08:50:00 +0800
From:   Yunsheng Lin <linyunsheng@...wei.com>
To:     Gal Pressman <gal@...dia.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 2022/10/27 17:03, Gal Pressman wrote:
> 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?

Yes.

> 
> 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?

If TX copybreak is using an inline WQE, I suppose 'TX copybreak buf size'
is not needed.

> .
>