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

[Chris Tyler]

On Wed, 2012-03-21 at 07:24 +0000, Gordan Bobic wrote:
> On 03/20/2012 08:00 PM, 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.
> 
> I disagree. ARMv5 is going to be around for a while yet, and the fix-up 
> in software at least needs to be implemented either by default or set as 
> the very first thing in rc.sysinit:
> 
> https://bugzilla.redhat.com/show_bug.cgi?id=673691

Agreed, alignment fixups must be enabled early.

> Otherwise not paying attention to alignment in something like e2fsprogs 
> could plausibly trash the file system:
> 
> https://bugzilla.redhat.com/show_bug.cgi?id=680090
> 
> Even if sloppy programming is not an issue on later ARMs, IMO the 
> alignment issues should be treated as bugs at least until ARMv5 support 
> is completely dropped.

Alignment issues happen on x86 too, but we accept the cost of the
hardware fixup and ignore them. Alignment issues are not necessarily
bugs; sometimes they're the result of conscious decisions that the fixup
is cheaper than the pages and pages of code required to avoid them in
the first place (e.g., in streamed data).

> > Anaconda isn't *quite* ready to go yet. And you don't actually gain much
> > by using Anaconda for many devices- you still have to write an image to
> > a removal storage device. Which you then run boot... and it writes a new
> > image to a storage device. You've just made more work for yourself when
> > you could have installed a working image directly.
> 
> In that case you might as well use the same installation procedure on 
> x86, too - there's no reason not to.

We do, after a fashion (and then wrap it in some extra layers): it's
called a Live Disc :-)

-Chris