netdev - Re: [PATCH V4 net-next 1/6] ethtool: add support to set/get tx copybreak buf size via ethtool

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Message-ID: <a8b9b95a-d7e3-53ad-cf87-9bb6f1610c5a@huawei.com>
Date:   Tue, 19 Oct 2021 21:44:36 +0800
From:   "huangguangbin (A)" <huangguangbin2@...wei.com>
To:     Eric Dumazet <eric.dumazet@...il.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 V4 net-next 1/6] ethtool: add support to set/get tx
 copybreak buf size via ethtool



On 2021/10/14 21:58, Eric Dumazet wrote:
> 
> 
> On 10/14/21 4:39 AM, Guangbin Huang wrote:
>> From: Hao Chen <chenhao288@...ilicon.com>
>>
>> Add support for ethtool to set/get tx copybreak buf size.
> 
> What is the unit ?
> 
> Frankly, having to size the 'buffer' based on number of slots in TX ring buffer
> is not good.
> 
> What happens later when/if ethtool -G tx xxxxx' is trying
> to change number of slots ?
> 
> The 'tx copybreak' should instead give a number of bytes per TX ring slot.
> 
> Eg, 128 or 256 bytes.
> 
> This is very similar to what drivers using net/core/tso.c do.
> 
> They usually use TSO_HEADER_SIZE for this.
> 
Hi Eric,
The unit is bytes.

Tx copybreak buf is a queue based tx shared bounce buffer and it is allocated
based on page size, not based on slot numbers. When the len of xmitted skb is
below tx_copybreak, tx copybreak buf will share buffer of specific size(slot size)
for tx to memcpy the small packet.

So, what you mentioned seems not related to this patch.

>>
>> Signed-off-by: Hao Chen <chenhao288@...ilicon.com>
>> Signed-off-by: Guangbin Huang <huangguangbin2@...wei.com>
>> ---
>>   include/uapi/linux/ethtool.h | 1 +
>>   net/ethtool/common.c         | 1 +
>>   net/ethtool/ioctl.c          | 1 +
>>   3 files changed, 3 insertions(+)
>>
>> diff --git a/include/uapi/linux/ethtool.h b/include/uapi/linux/ethtool.h
>> index a2223b685451..7bc4b8def12c 100644
>> --- a/include/uapi/linux/ethtool.h
>> +++ b/include/uapi/linux/ethtool.h
>> @@ -231,6 +231,7 @@ enum tunable_id {
>>   	ETHTOOL_RX_COPYBREAK,
>>   	ETHTOOL_TX_COPYBREAK,
>>   	ETHTOOL_PFC_PREVENTION_TOUT, /* timeout in msecs */
>> +	ETHTOOL_TX_COPYBREAK_BUF_SIZE,
>>   	/*
>>   	 * Add your fresh new tunable attribute above and remember to update
>>   	 * tunable_strings[] in net/ethtool/common.c
>> diff --git a/net/ethtool/common.c b/net/ethtool/common.c
>> index c63e0739dc6a..0c5210015911 100644
>> --- a/net/ethtool/common.c
>> +++ b/net/ethtool/common.c
>> @@ -89,6 +89,7 @@ tunable_strings[__ETHTOOL_TUNABLE_COUNT][ETH_GSTRING_LEN] = {
>>   	[ETHTOOL_RX_COPYBREAK]	= "rx-copybreak",
>>   	[ETHTOOL_TX_COPYBREAK]	= "tx-copybreak",
>>   	[ETHTOOL_PFC_PREVENTION_TOUT] = "pfc-prevention-tout",
>> +	[ETHTOOL_TX_COPYBREAK_BUF_SIZE] = "tx-copybreak-buf-size",
>>   };
>>   
>>   const char
>> diff --git a/net/ethtool/ioctl.c b/net/ethtool/ioctl.c
>> index bf6e8c2f9bf7..617ebc4183d9 100644
>> --- a/net/ethtool/ioctl.c
>> +++ b/net/ethtool/ioctl.c
>> @@ -2383,6 +2383,7 @@ static int ethtool_tunable_valid(const struct ethtool_tunable *tuna)
>>   	switch (tuna->id) {
>>   	case ETHTOOL_RX_COPYBREAK:
>>   	case ETHTOOL_TX_COPYBREAK:
>> +	case ETHTOOL_TX_COPYBREAK_BUF_SIZE:
>>   		if (tuna->len != sizeof(u32) ||
>>   		    tuna->type_id != ETHTOOL_TUNABLE_U32)
>>   			return -EINVAL;
>>
> .
>