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Re: [PATCH] xen/smp: Speed up on_selected_cpus()
- To: Andrew Cooper <Andrew.Cooper3@xxxxxxxxxx>
- From: Jan Beulich <jbeulich@xxxxxxxx>
- Date: Tue, 8 Feb 2022 11:39:51 +0100
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- Cc: Roger Pau Monne <roger.pau@xxxxxxxxxx>, Wei Liu <wl@xxxxxxx>, Juergen Gross <jgross@xxxxxxxx>, Stefano Stabellini <sstabellini@xxxxxxxxxx>, Julien Grall <julien@xxxxxxx>, Volodymyr Babchuk <Volodymyr_Babchuk@xxxxxxxx>, Bertrand Marquis <bertrand.marquis@xxxxxxx>, Xen-devel <xen-devel@xxxxxxxxxxxxxxxxxxxx>
- Delivery-date: Tue, 08 Feb 2022 10:40:05 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
On 07.02.2022 18:06, Andrew Cooper wrote:
> On 07/02/2022 08:11, Jan Beulich wrote:
>> (And of
>> course I still have that conversion to POPCNT alternatives patching pending,
>> where Roger did ask for some re-work in reply to v2, but where it has
>> remained unclear whether investing time into that wouldn't be in vein,
>> considering some of your replies on v1. Thus would have further shrunk the
>> difference, without me meaning to say the change here isn't a good one.)
>
> There is a perfectly clear and simple way forward. It's the one which
> doesn't fight the optimiser and actively regress the code generation in
> the calling functions, and add an unreasonable quantity technical debt
> into the marginal paths.
>
> I will ack a version where you're not adding complexity for negative gains.
Thanks, at least some form of a reply. I'm afraid I can't really translate
this to which parts of the change you'd be okay with and which parts need
changing. I didn't think I would "fight the optimiser and actively regress
the code generation in the calling functions" in v2 (this may have been
different in v1, but I haven't gone back to check; I wonder though whether
you're mixing this with e.g. the BMI patching series I've long given up on).
Jan
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