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Subject: Re: [PATCH V3 net-next 2/4] ethtool: extend coalesce setting uAPI
 with CQE mode
To:     Jakub Kicinski <kuba@kernel.org>,
        Grygorii Strashko <grygorii.strashko@ti.com>
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From:   moyufeng <moyufeng@huawei.com>
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Date:   Mon, 23 Aug 2021 11:06:59 +0800
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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/