On Fri, May 6, 2011 at 7:51 AM, Gordan Bobic <gordan(a)bobich.net> wrote:
Matt Domsch wrote:
> On Wed, May 04, 2011 at 01:46:06PM -0500, Jon Masters wrote:
>> Folks,
>>
>> I'd like to kick off a discussion about flags for ARMv7. My proposal
>> here is that we treat v7hl as an entirely different architecture, and
>> don't try any multi-arch kind of hacks (there isn't the established user
>> base for Fedora ARM to justify doing any of those things at the moment).
>>
>> Things I think we should consider as a minimum:
>>
>> *). Little endian (obviously, but worth stating) (l)
>> *). Cortex-A8 or higher fully compliant core(s)
>
> Is there a measureable difference in code optimized for A8 vs A9 when
> running on A9? If so, my inclination would be to build for the future
> - A9. It's not like A9 hardware is hard to come by these days.
I think the key thing to consider is cost/benefit. If the code optimized
for A9 runs poorly on A8, but the code optimized for A8 runs on A9
almost as well as the code optimized for the A9, then it would be better
to optimize for the A8.
Since A8 doesn't have OoOE, it wouldn't surprise me if latter was the
case (A8 code running imperceptibly worse on A9 but A9 code running
much worse on A8).
There is also the more philosophical issue - A9 is already faster than
A8, so it may be better to target the A8 on the basis that it is more in
need of that extra boost.
Having said that, the only real hardware platforms that are likely to be
affected here are the Genesi Efika and the Beagleboard. Everything else
that is popular seems to be either ARMv5 (Sheeva/Guru plugs) or A9
(AC100, Pandaboard, Trimslice).
Actually there's dozens of devices that use A8 processors. The Nokia
n900 and dozens of other phones. They may or may not be desirable to
support but there are a number of other tablet or netbook devices that
would be nice to be able to use.
Peter