Re: [RFC 2/5] tune-xscale, tune-arm926ejs: add OPTDEFAULTTUNE variable and use more generic DEFAULTTUNE as default

[Mark Hatle <mark.hatle@windriver.com>]

Let me preface this by I have read the patch set.. Martin asked me to comment on 
the items below...

On 9/27/12 3:37 AM, Martin Jansa wrote:
> On Sat, Sep 22, 2012 at 06:45:44PM +0100, Richard Purdie wrote:
>> On Sat, 2012-09-22 at 18:51 +0200, Martin Jansa wrote:
>>> * bitbake.conf has OPTDEFAULTTUNE with weak default value of DEFAULTTUNE
>>> * this way xscale or arm926ejs is not used by default when some machine
>>>    includes its tune*.inc, but it's easy for DISTRO to say it wants
>>>    OPTDEFAULTTUNE for some packages or always (if they don't want to
>>>    share built packages between xscale and arm926ejs).
>>>
>>> Signed-off-by: Martin Jansa <Martin.Jansa@gmail.com>
>>> ---
>>>   meta/conf/bitbake.conf                       | 1 +
>>>   meta/conf/machine/include/tune-arm926ejs.inc | 3 ++-
>>>   meta/conf/machine/include/tune-xscale.inc    | 3 ++-
>>>   3 files changed, 5 insertions(+), 2 deletions(-)
>>>
>>> diff --git a/meta/conf/bitbake.conf b/meta/conf/bitbake.conf
>>> index 9b41749..e433fcb 100644
>>> --- a/meta/conf/bitbake.conf
>>> +++ b/meta/conf/bitbake.conf
>>> @@ -95,6 +95,7 @@ HOST_LD_ARCH = "${TARGET_LD_ARCH}"
>>>   HOST_AS_ARCH = "${TARGET_AS_ARCH}"
>>>   HOST_EXEEXT = ""
>>>
>>> +OPTDEFAULTTUNE ??= "${DEFAULTTUNE}"
>>>   TUNE_ARCH ??= "INVALID"
>>>   TUNE_CCARGS ??= ""
>>>   TUNE_LDARGS ??= ""
>>
>> As I've said previously, I do not think OPTDEFAULTTUNE is clear in usage
>> or in meaning and we need to find a better solution. I'm therefore not
>> keen on this change.
>
> OK, what about the rest of patchset (without OPTDEFAULTTUNE bits) to use
> different PKGARCH for different TUNE_CCARGS?

I've been an advocate for a while that the processor optimization (CCARGS) does 
make it into the PKGARCH.  ARMPKGSFX_CPU seems like a reasonable approach to do 
this.  It allows each tune to set something to tell people what that binary is 
really built for, and for the 'base' tunes (i.e. armv5) it can be left off.

The only concern I have with that is:

+ARMPKGSFX_CPU = "${@bb.utils.contains("TUNE_FEATURES", "arm926ejs", 
"-arm926ejs", "", d)}"

That probably should be a .= instead of just '='.  That way if the user loads 
multiple compatible tunes the right ARMPKGSFX_CPU will be used.  (Alternatively 
using the overrides would work as well for this.. i.e. 
ARMPKGSFX_CPU_tune-arm926ejs instead...

I see Patch 5/5 instead moves toward the ARMPKGARCH usage instead...  This is 
fine as well, and it was designed to be overriden.. but again the .= or 
-tune_... syntax should be used...

Anyway, my point in this is I like having the stuff unique, but we need to be 
sure that you can specify more then one tune file during a build w/o clashes.

>> I also still think this is a distro packaging issue and should be solved
>> by the distro, even if that means more complexity there. That is the
>> right place for this particular complexity IMO. I'm happy to support
>> that from the core but not in something as user visible and confusing as
>> this variable.
>
> Agreed OPTDEFAULTTUNE is to help distro configs, because complexity
> there will be much worse then when it's defined in tune-* files, because
> now will have to define DEFAULTTUNE/OPTDEFAULTTUNE for each MACHINE (or
> TUNE_FEATURE) it supports and it's less orthogonal (machine/distro
> config) then it could be.

I really don't have a strong opinion on this either way.  I know for the stuff 
I've done in the past (not oe-based) we've just manually configured (the 
equivalent of the distro conf) with the information on the handful of items that 
people wanted optimized the most...  eglibc, openssl, mysql/posgresql... 
otherwise folks don't seem to care, and re-use works fine.

If the list is small (i.e. less then 10 packages) that specifying it via package 
specific overrides in the distro file should be fine.. if it's more then 10 
(typically) then we need to start looking for another approach.

I'd almost suggest in the distro file you could do:

OPTDEFAULTTUNE = "$@{...}" where ... is check for something set by the BSP (or 
elsewhere), if set use that value, otherwise using the DEFAULTTUNE value.

DEFAULTTUNE-<pn> = "${OPTDEFAULTTUNE}"

and then everything can be encapsulated into the distro file (and distro BSPs). 
  The downside of this approach is that it's not the 'standard' implementation.

--Mark

> Cheers,
>
>
>
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