netdev - Re: [PATCH 2/3] net:ethernet:rmnet:Support for downlink MAPv5 csum offload

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Message-ID: <f950b355214bd78f80df24391b85c4cc@codeaurora.org>
Date:   Fri, 12 Feb 2021 13:11:26 -0700
From:   subashab@...eaurora.org
To:     Alex Elder <elder@...e.org>
Cc:     Jakub Kicinski <kuba@...nel.org>,
        Sharath Chandra Vurukala <sharathv@...eaurora.org>,
        davem@...emloft.net, elder@...nel.org, cpratapa@...eaurora.org,
        netdev@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/3] net:ethernet:rmnet:Support for downlink MAPv5 csum
 offload

On 2021-02-12 12:06, Alex Elder wrote:
> On 2/12/21 12:51 PM, Jakub Kicinski wrote:
>> On Fri, 12 Feb 2021 08:01:15 -0600 Alex Elder wrote:
>>> On 2/11/21 8:04 PM, Jakub Kicinski wrote:
>>>> On Fri, 12 Feb 2021 03:05:23 +0530 Sharath Chandra Vurukala wrote:
>>>>> +/* MAP CSUM headers */
>>>>> +struct rmnet_map_v5_csum_header {
>>>>> +	u8  next_hdr:1;
>>>>> +	u8  header_type:7;
>>>>> +	u8  hw_reserved:5;
>>>>> +	u8  priority:1;
>>>>> +	u8  hw_reserved_bit:1;
>>>>> +	u8  csum_valid_required:1;
>>>>> +	__be16 reserved;
>>>>> +} __aligned(1);
>>>> 
>>>> Will this work on big endian?
>>> 
>>> Sort of related to this point...
>>> 
>>> I'm sure the response to this will be to add two versions
>>> of the definition, surrounded __LITTLE_ENDIAN_BITFIELD
>>> and __BIG_ENDIAN_BITFIELD tests.
>>> 
>>> I really find this non-intuitive, and every time I
>>> look at it I have to think about it a bit to figure
>>> out where the bits actually lie in the word.
>>> 
>>> I know this pattern is used elsewhere in the networking
>>> code, but that doesn't make it any easier for me to
>>> understand...
>>> 
>>> Can we used mask, defined in host byte order, to
>>> specify the positions of these fields?
>>> 
>>> I proposed a change at one time that did this and
>>> this *_ENDIAN_BITFIELD thing was used instead.
>>> 
>>> I will gladly implement this change (completely
>>> separate from what's being done here), but thought
>>> it might be best to see what people think about it
>>> before doing that work.
>> 
>> Most definitely agree, please convert.
> 
> KS, would you like me to do this to the existing code
> first?
> 
> I don't think it will take me very long.  If it were
> a priority I could probably get it done by the end of
> today, but I'd want to ensure the result worked for
> the testing you do.
> 
> 					-Alex

Sorry, I am not convinced that it is helping
to improve anything. It just adds a big
overhead of testing everything again without any
apparent improvement of performance or readablity
of code.