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Re: [PATCH v3 07/14 RESEND] cpufreq: Export HWP parameters to userspace
- To: Jason Andryuk <jandryuk@xxxxxxxxx>
- From: Jan Beulich <jbeulich@xxxxxxxx>
- Date: Mon, 8 May 2023 12:46:57 +0200
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- Cc: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>, Roger Pau Monné <roger.pau@xxxxxxxxxx>, Wei Liu <wl@xxxxxxx>, George Dunlap <george.dunlap@xxxxxxxxxx>, Julien Grall <julien@xxxxxxx>, Stefano Stabellini <sstabellini@xxxxxxxxxx>, xen-devel@xxxxxxxxxxxxxxxxxxxx
- Delivery-date: Mon, 08 May 2023 10:47:25 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
On 08.05.2023 12:25, Jan Beulich wrote:
> On 01.05.2023 21:30, Jason Andryuk wrote:
>> Extend xen_get_cpufreq_para to return hwp parameters. These match the
>> hardware rather closely.
>>
>> We need the features bitmask to indicated fields supported by the actual
>> hardware.
>>
>> The use of uint8_t parameters matches the hardware size. uint32_t
>> entries grows the sysctl_t past the build assertion in setup.c. The
>> uint8_t ranges are supported across multiple generations, so hopefully
>> they won't change.
>
> Still it feels a little odd for values to be this narrow. Aiui the
> scaling_governor[] and scaling_{max,min}_freq fields aren't (really)
> used by HWP. So you could widen the union in struct
> xen_get_cpufreq_para (in a binary but not necessarily source compatible
> manner), gaining you 6 more uint32_t slots. Possibly the somewhat oddly
> placed scaling_cur_freq could be included as well ...
Having seen patch 9 now as well, I wonder whether here (or in a separate
patch) you don't want to limit providing inapplicable data (for example
not filling *scaling_available_governors would even avoid an allocation,
thus removing a possible reason for failure), while there (or again in a
separate patch) you'd also limit what the tool reports (inapplicable
output causes confusion / questions at best).
Jan
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