[fedora-arm] Fedora 20 for Raspberry Pi????

[Sean Omalley]

> On Wednesday, January 1, 2014 6:52 AM, Richard W.M. Jones <rjones at redhat.com> wrote:
> > On Wed, Jan 01, 2014 at 10:22:29AM +0000, Gordan Bobic wrote:
>>  On 01/01/2014 10:18 AM, Richard W.M. Jones wrote:
>>  >On Mon, Dec 30, 2013 at 10:27:38PM +0800, Andy Green wrote:
>>  >>Yeah I think until you realize why and how it's a problem (in 
> other
>>  >>words, you got bitten) most programmers wouldn't particularly 
> think
>>  >>to defend against it because the code is c-legal and works on x86.
>>  >
>>  >That's because it *isn't* a problem.
>>  >
>>  >We shouldn't worry about misalignment problems in Fedora ARM unless
>>  >you can demonstrate with hard numbers that a particular misalignment
>>  >causes a performance issue.
>>  >
>>  >Set alignment to fixup, and forget about it.
>> 
>>  How dare anyone suggest the developers be educated and the problem
>>  be fixed rather than worked around.
> 
> There's nothing to educate about.  It's a non-problem except in a
> narrow performance case.
> 
> Most developers don't need to worry about swap, for precisely the same
> reason.  Alignment fixups, swapping, cache lines, TLBs, huge pages, ...
> are details of the implementation, and you don't need to think about
> them unless you're chasing a performance problem.
> 

They are a problem. It is a performance issue at the very least on =ALL= platforms. There is a cost even on Intel's platform for alignment errors, they just fix them up in hardware so it isn't as big of a performance hit. It might be 5 cycles instead of 20. 


C is a language where the programmer has to know what they are doing.  You don't depend on the compiler to do the "right thing". In other words, you get the keys, if you decide to drive into a brick wall going 100mph, it will let you. It doesn't care. You fsck'd up. 

You aren't a good programmer if you are knowingly introducing errors into your program and are relying on hardware to fix them. Then make the excuse, the hardware fixes the problem, therefore it isn't a problem. That is just lame. 

It used to be the trick was identifying the issue and most projects would fix it up, sooner rather then later. Because it is rather embarrassing.