netdev - Re: [PATCH V2 net-next 1/6] ethtool: add support to set/get tx copybreak buf size via ethtool

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Date:   Wed, 29 Sep 2021 10:19:51 +0800
From:   "huangguangbin (A)" <huangguangbin2@...wei.com>
To:     Michal Kubecek <mkubecek@...e.cz>
CC:     <davem@...emloft.net>, <kuba@...nel.org>, <andrew@...n.ch>,
        <amitc@...lanox.com>, <idosch@...sch.org>, <danieller@...dia.com>,
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        <jdike@...toit.com>, <richard@....at>,
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        <csully@...gle.com>, <awogbemila@...gle.com>, <jdmason@...zu.us>,
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        <pv-drivers@...are.com>, <jwi@...ux.ibm.com>,
        <kgraul@...ux.ibm.com>, <hca@...ux.ibm.com>, <gor@...ux.ibm.com>,
        <johannes@...solutions.net>, <netdev@...r.kernel.org>,
        <lipeng321@...wei.com>, <chenhao288@...ilicon.com>,
        <linux-s390@...r.kernel.org>
Subject: Re: [PATCH V2 net-next 1/6] ethtool: add support to set/get tx
 copybreak buf size via ethtool



On 2021/9/25 7:05, Michal Kubecek wrote:
> On Fri, Sep 24, 2021 at 10:29:54PM +0800, Guangbin Huang wrote:
>> From: Hao Chen <chenhao288@...ilicon.com>
>>
>> Add support for ethtool to set/get tx copybreak buf size.
>>
>> Signed-off-by: Hao Chen <chenhao288@...ilicon.com>
>> Signed-off-by: Guangbin Huang <huangguangbin2@...wei.com>
>> ---
>>   Documentation/networking/ethtool-netlink.rst | 24 ++++++++++++++++++++
>>   include/uapi/linux/ethtool.h                 |  1 +
>>   net/ethtool/common.c                         |  1 +
>>   net/ethtool/ioctl.c                          |  1 +
>>   4 files changed, 27 insertions(+)
>>
>> diff --git a/Documentation/networking/ethtool-netlink.rst b/Documentation/networking/ethtool-netlink.rst
>> index d9b55b7a1a4d..a47b0255aaf9 100644
>> --- a/Documentation/networking/ethtool-netlink.rst
>> +++ b/Documentation/networking/ethtool-netlink.rst
>> @@ -1521,6 +1521,30 @@ Kernel response contents:
>>     ``ETHTOOL_A_PHC_VCLOCKS_INDEX``       s32     PHC index array
>>     ====================================  ======  ==========================
>>   
>> +TUNABLE_SET
>> +===========
>> +
>> +Request contents:
>> +
>> +  =====================================  ======  ==========================
>> +  ``ETHTOOL_TX_COPYBREAK_BUF_SIZE``      u32     buf size for tx copybreak
>> +  =====================================  ======  ==========================
>> +
>> +Tx copybreak buf size is used for tx copybreak feature, the feature is used
>> +for small size packet or frag. It adds a queue based tx shared bounce buffer
>> +to memcpy the small packet when the len of xmitted skb is below tx_copybreak
>> +(value to distinguish small size and normal size), and reduce the overhead
>> +of dma map and unmap when IOMMU is on.
>> +
>> +TUNABLE_GET
>> +===========
>> +
>> +Kernel response contents:
>> +
>> +  ====================================  ======  ==========================
>> +  ``ETHTOOL_TX_COPYBREAK_BUF_SIZE``     u32     buf size for tx copybreak
>> +  ====================================  ======  ==========================
> 
> I have to repeat my concerns expressed in
> 
>    https://lore.kernel.org/netdev/20210826072618.2lu6spapkzdcuhyv@lion.mk-sys.cz
> 
> and earlier in more details in
> 
>    https://lore.kernel.org/netdev/20200325164958.GZ31519@unicorn.suse.cz
> 
> That being said, I don't understand why this patch adds description of
> two new message types to the documentation of ethtool netlink API but it
> does not actually add them to the API. Instead, it adds the new tunable
> to ioctl API.
> 
> Michal
> 

Hi Michal, thanks for your opinion.
Is there any documentation for ioctl API? We didn't find it.
Or we add a new documentation of ioctl API for the new tunable?

Guangbin