linux-kernel - Re: [PATCH 6/7] thermal: netlink: Add a new event to notify CPU capabilities change

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Message-ID: <f31278f5-7d23-b213-0b5b-321a0d7a048a@linaro.org>
Date:   Thu, 9 Dec 2021 17:57:35 +0100
From:   Daniel Lezcano <daniel.lezcano@...aro.org>
To:     Ricardo Neri <ricardo.neri-calderon@...ux.intel.com>
Cc:     "Rafael J. Wysocki" <rafael.j.wysocki@...el.com>,
        linux-pm@...r.kernel.org, x86@...nel.org,
        linux-doc@...r.kernel.org, Len Brown <len.brown@...el.com>,
        Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>,
        Aubrey Li <aubrey.li@...ux.intel.com>,
        Amit Kucheria <amitk@...nel.org>,
        Andi Kleen <ak@...ux.intel.com>,
        Tim Chen <tim.c.chen@...ux.intel.com>,
        "Ravi V. Shankar" <ravi.v.shankar@...el.com>,
        Ricardo Neri <ricardo.neri@...el.com>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 6/7] thermal: netlink: Add a new event to notify CPU
 capabilities change

On 09/12/2021 17:03, Ricardo Neri wrote:
> On Tue, Nov 30, 2021 at 10:29:46AM +0100, Daniel Lezcano wrote:
>> On 06/11/2021 02:33, Ricardo Neri wrote:
>>> From: Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>
>>>
>>> Add a new netlink event to notify change in CPU capabilities in terms of
>>> performance and efficiency.
>>>
>>> Firmware may change CPU capabilities as a result of thermal events in the
>>> system or to account for changes in the TDP (thermal design power) level.
>>>
>>> This notification type will allow user space to avoid running workloads
>>> on certain CPUs or proactively adjust power limits to avoid future events.
>>>
>>
>> [ ... ]
>>
>>> +	[THERMAL_GENL_ATTR_CPU_CAPABILITY_ID]	= { .type = NLA_U32 },
>>> +	[THERMAL_GENL_ATTR_CPU_CAPABILITY_PERF]	= { .type = NLA_U32 },
>>> +	[THERMAL_GENL_ATTR_CPU_CAPABILITY_EFF]	= { .type = NLA_U32 },
>>>  };
>>
>> AFAIU, 0 <= perf < 256 and 0 <= eff < 256, right?
>>
>> Is the following true?
>>
>> 	0 <= perf + eff < 256
> 
> No, they are not. They are set independently.

I understand they can be set independently but is the constraint above
correct? For example, can the system send perf=255 and eff=255 or perf=0
and eff=0 ?

May be I misunderstood but I was expecting at least some kind of
connection between perf and eff (when eff is high, perf is low and the
opposite).


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