ARM network trouble after recent mbuf changes

[Andre Oppermann]

On 27.08.2013 08:30, Michael Tuexen wrote:
> On Aug 27, 2013, at 7:53 AM, Hans Petter Selasky <hps at bitfrost.no> wrote:
>
>> On 08/27/13 00:38, Michael Tuexen wrote:
>>> I did some tests with a small program. Having in struct pkthdr 64 bit entities
>>> results in a 64 bit alignment when used in struct mbuf. Using __packed
>>> for struct mbuf, removes the padding.
>>
>>
>> Hi,
>>
>> Maybe you could use __aligned(8) instead, and account for the extra padding on all platforms? Packed has other disadvantages on ARM platforms when accessing the structures, like that non-aligned access is possible, and that it is sometimes slower than aligned access.
> Isn't there a performance penalty when accessing 64-bit entities not being 64-bit
> aligned? If that is the case, wouldn't it make sense to add a 4 byte padding to
> struct m_hdr for ILP32? Then the problem should go away...

Either that or define MLEN and MHLEN in a way that actually reflects the true
size of what they are representing.  The latter is the true bug.

> We could also get rid of the 64 bit alignment by not having 64-bit entities in
> struct pkthdr. Removing sixtyfour should be easy. However, we now have also
> uint64_t csum_flags.

Yes, the 64 bit fields are to be used to store packet associated information
on its way through the stack.  Reducing it to 32 bits would somewhat defeat
their purpose.

-- 
Andre