linux-kernel - Re: [PATCH v2 2/4] powercap: idle_inject: Add prepare/complete callbacks

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Message-ID: <de6a5000-260e-bb4a-31c4-a0cfe533fad4@linaro.org>
Date:   Thu, 22 Dec 2022 10:50:29 +0100
From:   Daniel Lezcano <daniel.lezcano@...aro.org>
To:     srinivas pandruvada <srinivas.pandruvada@...ux.intel.com>,
        rafael@...nel.org
Cc:     linux-pm@...r.kernel.org, linux-kernel@...r.kernel.org,
        rui.zhang@...el.com, amitk@...nel.org
Subject: Re: [PATCH v2 2/4] powercap: idle_inject: Add prepare/complete
 callbacks


Hi Srinivas,


On 21/12/2022 21:58, srinivas pandruvada wrote:
> Hi Daniel,
> 
> On Wed, 2022-12-21 at 15:52 +0100, Daniel Lezcano wrote:
>>
>> Hi Srinivas,
>>
>> On 30/11/2022 00:34, Srinivas Pandruvada wrote:
>>> The actual idle percentage can be less than the desired because of
>>> interrupts. Since the objective for CPU Idle injection is for
>>> thermal
>>> control, there should be some way to compensate for lost idle
>>> percentage.
>>> Some architectures provide interface to get actual idle percent
>>> observed
>>> by the hardware. So, the idle percent can be adjusted using the
>>> hardware
>>> feedback. For example, Intel CPUs provides package idle counters,
>>> which
>>> is currently used by intel powerclamp driver to adjust idle time.
>> Can you provide an example in terms of timings?
>>
>> I'm not getting how 'prepare' would do by returning a positive value
>> to
>> skip the play_idle_precise() and what will do 'complete' ?
>>
> intel_powerclamp has a logic where if the current idle percentage
> observed from hardware is more than the desired target inject percent,
> it skips calling play_idle().
> 
> For example if you want to inject 50% idle and system is naturally idle
> for 60%, there is no use of calling play_idle in the idle injection
> framework to induce more idle. In this way a workload can run
> immediately.
> 
> So trying to emulate the same logic by using powercap/idle_inject
> framework. So prepare() callback in the intel_powerclamp driver calls
> the existing function to check if idle-inject should skip for this time
> or not.

The function 'prepare' has the 'cpu' parameter. How can it compare with 
the desired idle duration as this information is not passed to the 
callback ?


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