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Re: [PATCH v5 18/18] xen/cpufreq: Adapt SET/GET_CPUFREQ_CPPC xen_sysctl_pm_op for amd-cppc driver
- To: "Penny, Zheng" <penny.zheng@xxxxxxx>
- From: Jan Beulich <jbeulich@xxxxxxxx>
- Date: Tue, 8 Jul 2025 09:14:44 +0200
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- Cc: "Huang, Ray" <Ray.Huang@xxxxxxx>, Anthony PERARD <anthony.perard@xxxxxxxxxx>, Andrew Cooper <andrew.cooper3@xxxxxxxxxx>, "Orzel, Michal" <Michal.Orzel@xxxxxxx>, Julien Grall <julien@xxxxxxx>, Roger Pau Monné <roger.pau@xxxxxxxxxx>, Stefano Stabellini <sstabellini@xxxxxxxxxx>, "xen-devel@xxxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxxx>
- Delivery-date: Tue, 08 Jul 2025 07:14:59 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
On 08.07.2025 06:02, Penny, Zheng wrote:
>> -----Original Message-----
>> From: Jan Beulich <jbeulich@xxxxxxxx>
>> Sent: Tuesday, June 17, 2025 6:38 PM
>>
>> On 27.05.2025 10:48, Penny Zheng wrote:
>>> --- a/tools/misc/xenpm.c
>>> +++ b/tools/misc/xenpm.c
>>> +
>>> + case XEN_SYSCTL_CPPC_SET_PRESET_BALANCE:
>>> + if ( set_cppc->set_params & XEN_SYSCTL_CPPC_SET_DESIRED )
>>> + return -EINVAL;
>>> + policy->policy = CPUFREQ_POLICY_BALANCE;
>>> + min_perf = data->caps.lowest_perf;
>>> + max_perf = data->caps.highest_perf;
>>> + epp = CPPC_ENERGY_PERF_BALANCE;
>>> + break;
>>
>> Isn't this more line "ondemand"? To me, "balance" would mean tying perf to
>> at least
>> close around the middle of lowest and highest.
>
> The "balance" word comes from the epp value, it is 127, which is the middle
> value
> In actual hardware algorithm, the value of Energy Performance Preference
> register(EPP) will be translated to frequency setting,
> And it sets the minimum active frequency.
> An EPP of zero sets the min active frequency to Fmax, while an EPP of 255
> sets the min active frequency to Fmin (~IdleFreq). It is linear scaling, so
> epp of 127 is calculated to the middle of Fmax and Fmin.
> And Fmax corresponds to the highest perf, and Fmin corresponds to the
> non-linear lowest perf
I'm fine with the EPP value picked here. My question - as to the min_perf and
max_perf values that you set - remains, though.
Jan
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