On 09/06/2023 9:17 am, Christian Lindig wrote:
>> On 8 Jun 2023, at 20:33, Andrew Cooper <andrew.coop...@citrix.com> wrote:
>>
>> +type arm_physinfo_caps =
>> + {
>> + sve_vl: int;
>> + }
>> +
>
> Does the OCaml side need to know about the structure of this value or is it
> enough to pass it around as an abstract value because all logic is on the C
> side? I assume the OCaml side needs at least a way to persist the value and
> hence needs to know some representation.
Yes, Ocaml does need to know about the structure.
info->arch_capabilities is a collection of misc info. It was intended
to be just a bitmap of things, hence why it's a list on the x86 side (We
added fields, then had to revert and I haven't got back around to
reworking that yet).
But now ARM have put a non-bit field field into it, where a toolstack
needs to select a domain_create sve_vl setting between min(0,
physinfo.sve_vl)
The Ocaml code doesn't have an #include <public/sysctl.h> so doesn't
have the masks/constants required to decompose the integer into it's
constitute parts.
>
>> Store_field(arch_obj, 0,
>> + Val_int(MASK_EXTR(info->arch_capabilities,
>> + XEN_SYSCTL_PHYSCAP_ARM_SVE_MASK) * 128));
>> +
> What is the “* 128” achieving as part of this encoding?
No functional change from before... except it was previously hidden in
a different header file which I'm in the process of deleting.
The vector length is a multiple of 128. This value is more amenable to
being understood in a log file by a human.
~Andrew
