netdev - Re: [PATCH V5 net-next 0/6] ethtool: add support to set/get tx copybreak buf size and rx buf len

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Message-ID: <f4937fea-4693-e534-38db-e8c64158ce55@huawei.com>
Date:   Mon, 1 Nov 2021 11:42:18 +0800
From:   "huangguangbin (A)" <huangguangbin2@...wei.com>
To:     Andrew Lunn <andrew@...n.ch>
CC:     <davem@...emloft.net>, <kuba@...nel.org>, <mkubecek@...e.cz>,
        <amitc@...lanox.com>, <idosch@...sch.org>, <danieller@...dia.com>,
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        <linux-s390@...r.kernel.org>
Subject: Re: [PATCH V5 net-next 0/6] ethtool: add support to set/get tx
 copybreak buf size and rx buf len



On 2021/10/31 1:58, Andrew Lunn wrote:
>> Rx buf len is buffer length of each rx BD. Use ethtool -g command to get
>> it, and ethtool -G command to set it, examples are as follow:
>>
>> 1. set rx buf len to 4096
>> $ ethtool -G eth1 rx-buf-len 4096
>>
>> 2. get rx buf len
>> $ ethtool -g eth1
>> ...
>> RX Buf Len:     4096
> 
> How does this interact with MTU? If i have an MTU of 1500, and i set
> the rx-buf-len to 1000, can i expect all frames to the discarded?
> Should the core return -EINVAL? Or do you think some hardware will
> simply allocate two buffers and scatter/gather over them? Which
> implies that drivers which cannot SG must check if the rx-buf-len is
> less than the MTU and return -EINVAL?
> 
>       Andrew
> .
> 
Yes, hns3 driver supports scatter/gather for this situation, it's necessary
for driver which cannot support SG to check if rx buf len is less than mtu.