Re: Raspbian checks and question for Jessie
On Wed, Jun 05, 2013 at 09:38:43PM +0200, Axel Beckert wrote:
> So what would be the consequences of redefining armhf's minimum
> hardware requirements, i.e. would there a noticable performance loss
> on more modern systems if armhf would be built to include armv6 in the
> future?
I believe the answer when armhf was originally defined is: Yes.
Main reason as far as I understand it is that ARMv7 has thumb2, which
is what armhf uses by default, which means the code size is smaller
while having the same execution speed as normal arm instructions,
but the smaller code size means less cache usage, so effectively your
instruction cache is made larger and more effective, which certainly
will help performance.
I am not sure if ARMv6 has the same VFP3-D16 as ARMv7, but I think
it does.
Neon was considered, but at the time the number of nvidia tegras seemed
important enough to not require it (since nvidia left out neon support
probably expecting you to use their GPU instead).
I think there might be some cache handling instructions and other
improvements in ARMv7 that can make some mutex and such faster too,
but I might remember wrong on those details.
There were just so many ARMv7 designs around and just about no ARMv6
designs at the time the decision was made. Then the Raspberry Pi
happened a few months later and changed the issue a bit in terms of
number of devices out there.
--
Len Sorensen
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