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Re: [PATCH v5 00/12] SVE feature for arm guests
- To: Luca Fancellu <Luca.Fancellu@xxxxxxx>
- From: Bertrand Marquis <Bertrand.Marquis@xxxxxxx>
- Date: Tue, 18 Apr 2023 13:13:26 +0000
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- Cc: Xen-devel <xen-devel@xxxxxxxxxxxxxxxxxxxx>, Wei Chen <Wei.Chen@xxxxxxx>, Stefano Stabellini <sstabellini@xxxxxxxxxx>, Julien Grall <julien@xxxxxxx>, Volodymyr Babchuk <Volodymyr_Babchuk@xxxxxxxx>, Andrew Cooper <andrew.cooper3@xxxxxxxxxx>, George Dunlap <george.dunlap@xxxxxxxxxx>, Jan Beulich <jbeulich@xxxxxxxx>, Wei Liu <wl@xxxxxxx>, Roger Pau Monné <roger.pau@xxxxxxxxxx>, Nick Rosbrook <rosbrookn@xxxxxxxxx>, Anthony PERARD <anthony.perard@xxxxxxxxxx>, Juergen Gross <jgross@xxxxxxxx>, Christian Lindig <christian.lindig@xxxxxxxxxx>, David Scott <dave@xxxxxxxxxx>, Marek Marczykowski-Górecki <marmarek@xxxxxxxxxxxxxxxxxxxxxx>, Henry Wang <Henry.Wang@xxxxxxx>, Community Manager <community.manager@xxxxxxxxxxxxxx>
- Delivery-date: Tue, 18 Apr 2023 13:13:58 +0000
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- Thread-topic: [PATCH v5 00/12] SVE feature for arm guests
Hi Luca,
On this serie I would like to open a discussion on how to handle the vector size
and the corresponding command line / configuration / device tree parameters.
In general the user must either give a vector size it wants or has a solution to
just request the maximum supported size.
In the current implementation if a size bigger than the supported one is
provided:
- we silently disable SVE for dom0
- we silently disable SVE for dom0less
- we do not create a guest when done through tools
This is not completely coherent and i think we should aim for a coherent
behaviour
unless we have arguments for this status.
Is there any good reason to silently disable for Dom0 and dom0less only ?
I see some possible solutions here:
- modify parameter behaviour to use the supported size if parameter is bigger
than
it. This would at least keep SVE enabled if a VM depends on it and could
simplify
some of the handling by using 2048 to use the maximum supported size.
- coherently stop if the parameter value is not supported (including if sve is
not supported)
- always disable SVE if the parameter value is not supported.
To be honest I am not quite sure which solution is better but I am not happy
with
the different kind of behaviour we have right now.
What are your thoughts ?
Regards
Bertrand
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