[OE-core] qemuarm: should it really have TUNE_ARCH armv5te?

[Martin Jansa]

On Tue, Sep 11, 2012 at 05:46:12PM +0100, Phil Blundell wrote:
> On Tue, 2012-09-11 at 15:01 +0200, Martin Jansa wrote:
> > Shouldn't spitz produce something like armv5te-xscale and qemuarm armv5te-arm926ejs?
> 
> That's a DISTRO policy decision really.
> 
> "armv5te", in common with most of the PACKAGE_ARCHes, represents an ISA.
> That is, it is guaranteed to only contain instructions which are
> supported by all v5TE cores (which includes both ARM926EJ-S and XScale).
> It obviously follows from this that packages with PACKAGE_ARCH=armv5te
> are suitable for running on both qemuarm and xscale MACHINEs.
> 
> Note that a binary that was built with -mtune=arm926ej-s is still an
> ARMv5TE binary and will run just fine on xscale.  It won't run quite as
> fast as one that was built -mtune=xscale, though the performance
> difference is not so great as to be completely crippling.  With current
> gcc, the reverse is true as well: a binary built -mtune=xscale is also
> still ARMv5TE and will run just fine on ARM926EJ-S, and in fact the
> performance penalty is less this way around.
> 
> Now, if your DISTRO feels that the performance difference is important
> enough to be worth distinguishing the packages, you can certainly
> arrange for those two tunings to get separate PACKAGE_ARCHes and
> maintain parallel feeds.  But in the general case it's not totally
> obvious that this would be worthwhile, and I'm not sure it is a very
> useful thing to do by default.

But that is default now, that's why I've started this thread.

It uses PACKAGE_ARCH=armv5te while using -mtune. Causing different
sstate checksums and rebuilds when you switch e.g. qemuarm and spitz.

If we drop DEFAULTTUNE from tune-xscale and tune-arm926ejs then
PACKAGE_ARCH=armv5te would be the same and the same feed will be built
only once.

And if DISTO feels that the performance difference is important then
something like OPTDEFAULTTUNE could be added:
http://lists.linuxtogo.org/pipermail/openembedded-core/2012-September/029455.html

Cheers,
-- 
Martin 'JaMa' Jansa     jabber: Martin.Jansa at gmail.com
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