Re: [PATCH v3 4/4] x86/APIC: make connections between seemingly arbitrary numbers

[Jan Beulich <jbeulich@xxxxxxxx>]

On 11.03.2022 15:24, Roger Pau Monné wrote:
> On Mon, Feb 14, 2022 at 10:25:57AM +0100, Jan Beulich wrote:
>> Making adjustments to arbitrarily chosen values shouldn't require
>> auditing the code for possible derived numbers - such a change should
>> be doable in a single place, having an effect on all code depending on
>> that choice.
>>
>> For one make the TDCR write actually use APIC_DIVISOR. With the
>> necessary mask constant introduced, also use that in vLAPIC code. While
>> introducing the constant, drop APIC_TDR_DIV_TMBASE: The bit has been
>> undefined in halfway recent SDM and PM versions.
>>
>> And then introduce a constant tying together the scale used when
>> converting nanoseconds to bus clocks.
>>
>> No functional change intended.
>>
>> Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
> 
> Reviewed-by: Roger Pau Monné <roger.pau@xxxxxxxxxx>

Thanks.

>> ---
>> I thought we have a generic "glue" macro, but I couldn't find one. Hence
>> I'm (ab)using _AC().
> 
> I would be fine if you want to introduce something right in this
> commit to cover those needs, using _AC is not overly nice (or
> clear) IMO.

Hmm, I was rather hoping that you (or someone else) would point me
at what I thought I'm overlooking. If anything I'd likely clone
Linux'es __PASTE() (avoiding the leading underscores), but their
placement in linux/compiler_types.h seems pretty arbitrary and
hence not a good guideline for placement in our tree. To be honest
the only thing that would seem halfway consistent to me would be a
separate header, yet that seems somewhat overkill ... Or wait -
maybe xen/lib.h could be viewed as kind of suitable. Of course
there's then the immediate question of whether to make _AC() use
the new macro instead of open-coding it.

Jan