[fedora-arm] ARM Primary FESCO discussion results, round 1

[Leif Lindholm]

On 03/20/12 20:00, Brendan Conoboy wrote:
> On 03/20/2012 02:48 AM, Gordan Bobic wrote:
>> Are alignment problems not considered bugs? It's not just that this will
>> break code on ARM<  v7 and IIRC SPARC, but alignment issues also cause
>> cache line straddling which has a performance impact.
>
> I took this question to be a case of
> knowing-just-enough-about-ARM-to-be-harmful.  It's really a non-issue,
> particularly since later ARM chips don't have the problem.

Well...

It is a real (but usually small) performance issue on on some ARMv7 
processors for the basic LDR/STR/LDRH/STRH instructions.

However, LDM/STM/LDRD/STRD still need to be word aligned. So you're 
still looking at the choice between an application crashing or a risk of 
a two-orders-of-magnitude slowdown of some accesses due to kernel fixup 
in the exception handler unless the code is fixed.

/
     Leif