Great explanation -- that cleared up a few questions I've had. Thanks, -Marc On Aug 7, 2014 5:31 PM, "Gordan Bobic" <[email protected]> wrote:
> On 08/08/2014 12:17 AM, Robert Moskowitz wrote: > >> I see that the rpms are labeled: armv5tel >> >> My Cubieboard is an armv7 (Allwinner A20 duo core) >> >> This bothers me a bit. I don't know if there are better and newer >> instructions available with the armv7 or if it is just more stuff. Or if >> the new stuff is all handled in the kernel. Or. Or. >> >> So what is the story here. Does Redsleeve need to be compiled >> specifically for the armv7 or does the armv5tel support all that is there? >> > > RedSleeve only comes with armv5tel soft-float support. Some packages in > the epel repository are armv6l, some may even be armv7l, but all are > soft-float. There are additional instructions available in higher target > platforms, but they make relatively little difference (a bit like on x86 > where back in the day there was just no point in specifically targetting, > say, i586, so all the binaries were targetted at i386 because the benefit > of more specialised binaries was not significant enough to justify the > overhead of maintaining multiple package sets. > > On ARM, the significant improvement comes from hard-float support, but > even that is mostly limited to apps that do heavy floating point number > crunching, and the difference in most desktop and server apps is negligible. > > Soft-float and hard-float are mutually ABI incompatible. You cannot run a > mixed set of soft-float and hard-float binaries on the same system like you > can with x86 and x86-64 because multilib support for that was never worked > out due to being too difficult and not giving enough benefits to be worth > bothering with. But as long as binaries are all soft-float (or all > hard-float) it doesn't matter what instruction set they are targetting, > they will interoperate cleanly as long as the CPU has the required > instructions. (Note: hard-float requires ARMv7 as FPU was not available on > ARMv5, and it was optional on ARMv6; ARMv7 must have a FPU, ARMv6 isn't > guaranteed to have it.) > > It is also worth mentioning that soft-float binaries CAN use the hardware > FPU if it is present. It's just that the overhead of using the hardware FPU > can be higher in the setup phase, so for small amounts of short FP > operations it is usually quicker to just emulate it. > > As far as RedSleeve EL6 is concerned - there is no hard-float version, nor > will there be. The EL6 (F11-F13) era toolchain doesn't support hard-float > sufficiently completely and sufficiently stably to facilitate it. You could > rebuild the entire distribution with a much more recent toolchain, but then > it would arguably be pretty far from being EL6 in terms of versions of key > libraries. > > So, diet version - on RSEL6 there is only soft-float armv5tel in the main > repository, and EPEL includes some higher soft-float variants but they are > all soft float because that is all the toolchain supports reliably. None of > this is of major concern in terms of performance unless you plan to do > gaming or other similarly heavy FP number crunching. > > Even more diet version - don't worry about it. Yum will do the right > thing, and for the packages for which armv6l or armv7l variants exist, it > will pick those if your CPU can handle it. > > Gordan > _______________________________________________ > users mailing list > [email protected] > http://lists.redsleeve.org/mailman/listinfo/users >
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