Re: [PATCH for-4.17 v4 2/2] amd: remove VIRT_SC_MSR_HVM synthetic feature

[Roger Pau Monné <roger.pau@xxxxxxxxxx>]

On Wed, Nov 16, 2022 at 08:41:06AM +0100, Jan Beulich wrote:
> On 16.11.2022 00:54, Andrew Cooper wrote:
> > On 15/11/2022 16:44, Jan Beulich wrote:
> >> I think we need to settle on at least halfway firm rules on when to use
> >> synthetic feature bits and when to use plain global booleans. Without
> >> that the tastes of the three of us are going to collide again every once
> >> in a while.
> > 
> > Its very easy.  All other things being equal, synthetic features are the
> > most efficient option.
> 
> See Roger's better wording of "why use a more complicated construct when
> a simple one will do". Yes, generated code may be better in certain cases,
> but no, we don't always judge by that aspect alone. Source simplicity is
> an important criteria, which at other times I recall you also weighing
> higher than the performance of resulting code (especially when dealing
> with performance aspects when they don't really matter at most/all use
> sites of whichever construct).

I think it would be easier if we can discuss this in one of our x86
related meetings.  It's still unclear to me why a synthetic feature
would be preferred rather than a global variable in most cases (like
the one here, even if the variable didn't end up having the __init
attribute).

Thanks, Roger.