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Re: [PATCH for-4.17 v4 2/2] amd: remove VIRT_SC_MSR_HVM synthetic feature
- To: Andrew Cooper <Andrew.Cooper3@xxxxxxxxxx>
- From: Jan Beulich <jbeulich@xxxxxxxx>
- Date: Wed, 16 Nov 2022 08:41:06 +0100
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- Cc: "Henry.Wang@xxxxxxx" <Henry.Wang@xxxxxxx>, Wei Liu <wl@xxxxxxx>, Roger Pau Monne <roger.pau@xxxxxxxxxx>, "xen-devel@xxxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxxx>
- Delivery-date: Wed, 16 Nov 2022 07:41:22 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
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).
Jan
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