Re: [MirageOS-devel] Mirage on Xen/ARM status

[Anil Madhavapeddy <anil@xxxxxxxxxx>]

On 13 Jun 2014, at 10:15, Thomas Leonard <talex5@xxxxxxxxx> wrote:

> On 13 June 2014 10:09, Anil Madhavapeddy <anil@xxxxxxxxxx> wrote:
>> On 12 Jun 2014, at 15:46, Thomas Leonard <talex5@xxxxxxxxx> wrote:
>>>> 
>>>> The next step is to get networking working on ARM.
>>> 
>>> This seems to be working now (I can telnet to port 80 and send it a
>>> message), which it displays on the console.
>> 
>> Fantastic!!
>> 
>>> The main problem turned out to be ones_complement_checksum_bigarray,
>>> which was doing unaligned double-word (64-bit) memory access. This
>>> faults on ARM. For testing, I replaced it with the version in the unix
>>> directory.
>> 
>> Interesting -- they were meant to be exactly the same if I remember.
>> Is there an actual code difference between the two aside from include
>> headers?
> 
> They are very different. Looks like one got optimised without the other here:
> 
> https://github.com/mirage/mirage-platform/commit/6fc97d77d0846bc7f17bd0702832ea1faa8a7e71
> 

Ah yes, istr the reasoning behind this was that the Unix one would never
be used in a high-performance context, so portability was more useful than
performance.

Still, being able to unify these is very desirable, as being able to test
the stack independently of Xen (and expecting similar behavioural 
characteristics)
is extremely important.

-anil
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