netdev - Re: [PATCH V3 net-next 2/4] ethtool: extend coalesce setting uAPI with CQE mode

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Date:   Tue, 24 Aug 2021 11:14:49 +0800
From:   moyufeng <moyufeng@...wei.com>
To:     Jakub Kicinski <kuba@...nel.org>,
        Grygorii Strashko <grygorii.strashko@...com>
CC:     <davem@...emloft.net>, <netdev@...r.kernel.org>,
        <shenjian15@...wei.com>, <lipeng321@...wei.com>,
        <yisen.zhuang@...wei.com>, <linyunsheng@...wei.com>,
        <huangguangbin2@...wei.com>, <chenhao288@...ilicon.com>,
        <salil.mehta@...wei.com>, <linuxarm@...wei.com>,
        <linuxarm@...neuler.org>, <dledford@...hat.com>, <jgg@...pe.ca>,
        <netanel@...zon.com>, <akiyano@...zon.com>,
        <thomas.lendacky@....com>, <irusskikh@...vell.com>,
        <michael.chan@...adcom.com>, <edwin.peer@...adcom.com>,
        <rohitm@...lsio.com>, <jacob.e.keller@...el.com>,
        <ioana.ciornei@....com>, <vladimir.oltean@....com>,
        <sgoutham@...vell.com>, <sbhatta@...vell.com>, <saeedm@...dia.com>,
        <ecree.xilinx@...il.com>, <merez@...eaurora.org>,
        <kvalo@...eaurora.org>, <linux-wireless@...r.kernel.org>
Subject: Re: [PATCH V3 net-next 2/4] ethtool: extend coalesce setting uAPI
 with CQE mode



On 2021/8/23 11:06, moyufeng wrote:
> 
> 
> On 2021/8/21 6:21, Jakub Kicinski wrote:
>> On Fri, 20 Aug 2021 21:27:13 +0300 Grygorii Strashko wrote:
>>> This is very big change which is not only mix two separate changes, but also looks
>>> half-done. From one side you're adding HW feature supported by limited number of HW,
>>> from another - changing most of net drivers to support it by generating mix of legacy
>>> and new kernel_ethtool_coalesce parameters.
>>>
>>> There is also an issue - you do not account get/set_per_queue_coalesce() in any way.
>>
>> ethtool's netlink interface does not support per queue coalescing.
>> I don't think it's fair to require it as part of this series.
>>
>>> Would it be possible to consider following, please?
>>>
>>> - move extack change out of this series
>>
>> Why? To have to change all the drivers twice?
>>
>>> - option (a)
>>>    add new callbacks in ethtool_ops as set_coalesce_cqe/get_coalesce_cqe for CQE support.
>>>    Only required drivers will need to be changed.
>>
>> All the params are changed as one operation from user space's
>> perspective. Having two ops would make it problematic for drivers 
>> to fail the entire op without modifying half of the parameters in 
>> a previous callback.
>>
>>> - option (b)
>>>    add struct ethtool_coalesce as first field of kernel_ethtool_coalesce
>>
>> This ends up being more painful than passing an extra parameter 
>> in my experience.
>>
>>> struct kernel_ethtool_coalesce {
>>> 	/* legacy */
>>> 	struct ethtool_coalesce coal;
>>>
>>> 	/* new */
>>> 	u8 use_cqe_mode_tx;
>>> 	u8 use_cqe_mode_rx;
>>> };
>>>
>>> --  then b.1
>>>    drivers can be updated as
>>>     static int set_coalesce(struct net_device *dev,
>>>     			    struct kernel_ethtool_coalesce *kernel_coal)
>>>     {
>>> 	struct ethtool_coalesce *coal = &kernel_coal->coal;
>>>     
>>>     (which will clearly indicate migration to the new interface )
>>>
>>> -- then b.2
>>>      add new callbacks in ethtool_ops as set_coalesce_ext/get_coalesce_ext (extended)
>>>      which will accept struct kernel_ethtool_coalesce as parameter an allow drivers to migrate when needed
>>>      (or as separate patch which will do only migration).
>>>
>>> Personally, I like "b.2".
>>
>> These options were considered. None of the options is great to 
>> be honest. Let's try the new params, I say. 
>> .
>>
> 
> Yes, these have been considered in previous RFCs. For details, please refer to [1].
> 
> [1]https://lore.kernel.org/netdev/20210526165633.3f7982c9@kicinski-fedora-pc1c0hjn.dhcp.thefacebook.com/
> 
> .
> 
Hi Grygorii & Jakub

Is this patch still good? Or do I need to resend this series
with RFC link above in change log?

Thanks