From: Lukasz Luba <lukasz.luba@arm.com>
To: "Rafael J. Wysocki" <rafael@kernel.org>
Cc: Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
Daniel Lezcano <daniel.lezcano@linaro.org>,
Linux PM <linux-pm@vger.kernel.org>,
Amit Kucheria <amitk@kernel.org>,
"Zhang, Rui" <rui.zhang@intel.com>,
Dietmar Eggemann <dietmar.eggemann@arm.com>,
Chris Redpath <Chris.Redpath@arm.com>,
Beata.Michalska@arm.com, Viresh Kumar <viresh.kumar@linaro.org>,
"Rafael J. Wysocki" <rjw@rjwysocki.net>,
Amit Kachhap <amit.kachhap@gmail.com>
Subject: Re: [RFC PATCH 2/4] cpuidle: Add Active Stats calls tracking idle entry/exit
Date: Tue, 22 Jun 2021 14:58:56 +0100 [thread overview]
Message-ID: <2f7d855c-5232-ddbe-8403-db3596dcebc5@arm.com> (raw)
In-Reply-To: <CAJZ5v0iGv_1d3BT0HowLgecOfhNHNQdOwH6Kef5WE4-zeBbp2Q@mail.gmail.com>
On 6/22/21 1:33 PM, Rafael J. Wysocki wrote:
> On Tue, Jun 22, 2021 at 9:59 AM Lukasz Luba <lukasz.luba@arm.com> wrote:
>>
>> The Active Stats framework tracks and accounts the activity of the CPU
>> for each performance level. It accounts the real residency,
>
> No, it doesn't. It just measures the time between the entry and exit
> and that's not the real residency (because it doesn't take the exit
> latency into account, for example).
It's 'just' a 'model' and as other models has limitations, but it's
better than existing one, which IPA has to use:
cpu_util + currect_freq_at_sampling_time
>
>> when the CPU was not idle, at a given performance level. This patch adds needed calls
>> which provide the CPU idle entry/exit events to the Active Stats
>> framework.
>
> And it adds overhead to overhead-sensitive code.
>
> AFAICS, some users of that code will not really get the benefit, so
> adding the overhead to it is questionable.
>
> First, why is the existing instrumentation in the idle loop insufficient?
The instrumentation (tracing) cannot be used at run time AFAIK. I need
this idle + freq information combined in a running platform, not for
post-processing (like we have in LISA). The thermal governor IPA would
use them for used power estimation.
>
> Second, why do you need to add locking to this code?
The idle entry/exit updates the CPU's accounting data structure.
There is a reader of those data structures: thermal governor,
run from different CPU, which is the reason why I put locking for them.
next prev parent reply other threads:[~2021-06-22 13:59 UTC|newest]
Thread overview: 21+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-06-22 7:59 [RFC PATCH 0/4] Introduce Active Stats framework with CPU performance statistics Lukasz Luba
2021-06-22 7:59 ` [RFC PATCH 1/4] PM: Introduce Active Stats framework Lukasz Luba
2021-06-22 7:59 ` [RFC PATCH 2/4] cpuidle: Add Active Stats calls tracking idle entry/exit Lukasz Luba
2021-06-22 12:33 ` Rafael J. Wysocki
2021-06-22 13:58 ` Lukasz Luba [this message]
2021-06-22 14:44 ` Rafael J. Wysocki
2021-06-22 15:02 ` Lukasz Luba
2021-06-22 7:59 ` [RFC PATCH 3/4] cpufreq: Add Active Stats calls tracking frequency changes Lukasz Luba
2021-06-22 9:32 ` Viresh Kumar
2021-06-22 11:07 ` Lukasz Luba
2021-06-23 3:15 ` Viresh Kumar
2021-06-23 9:14 ` Lukasz Luba
2021-06-22 12:28 ` Rafael J. Wysocki
2021-06-22 13:42 ` Lukasz Luba
2021-06-22 13:51 ` Rafael J. Wysocki
2021-06-22 14:09 ` Lukasz Luba
2021-06-22 14:51 ` Rafael J. Wysocki
2021-06-22 14:59 ` Rafael J. Wysocki
2021-06-22 15:10 ` Lukasz Luba
2021-06-22 15:02 ` Lukasz Luba
2021-06-22 7:59 ` [RFC PATCH 4/4] thermal: cpufreq_cooling: Improve power estimation based on Active Stats framework Lukasz Luba
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