Re: [PATCH v2] ath9k: collect statistics about Rx-Dup and Rx-STBC packets

[Oleksij Rempel <linux@rempel-privat.de>]

Am 27.04.2013 21:06, schrieb Adrian Chadd:
> On 27 April 2013 11:53, Oleksij Rempel <linux@rempel-privat.de> wrote:
>
>>> (And then go and re-align things inside that struct so you don't waste
>>> space.)
>>
>>
>> hmm.. what do you mean here?
>
> Structure alignment? Well, you typically want to have everything be
> dword aligned (32 bits) or word (16 bits) aligned. Otherwise the
> compiler may insert extra padding between fields in order to meet
> alignment requirements on platforms that need it (MIPS, older ARM) or
> platforms that perform slower (newer ARM.)
>
> Eg:
>
> u32 a;
> u16 b;
> u8 c;
> u8 d;
>
> .. that's fine - the u32 is dword aligned, the u16 is word aligned,
> the u8's don't need aligning.
>
> But, considder:
>
> u32 a;
> u8 b;
> u16 c;
> u8 d;
>
> .. u32 is dword aligned, u8 b is fine as it's a a byte and doesn't
> need aligning, but 'u16 c' isn't dword aligned! So the compiler will
> insert a byte padding between 'b' and 'c'.
>
> same deal with:
>
> u32 a;
> u16 b;
> u32 c;
>
> .. 'a' is fine; 'b' is fine, but 'c' starts at a word boundary, not a
> dword boundary.
>
> Hence why things like IP/TCP headers and such look the way they do. :-)
>
> Now, i don't know what 'bool' is, whether it's a byte, word or dword.
> That "is_mybeacon" field should probably be just another flag in
> rx_status, then just extend 'rs_flags' to 16 bits and include it. That
> way the alignment is easy to see - all the fields in rx_status and the
> htc rx_status structs have explicit sizes. :-)

ok, i was not sure if you mean what i think :)
I would prefer to do this in separate patch.

-- 
Regards,
Oleksij