From: Daniel Lezcano <daniel.lezcano@linaro.org>
To: "Rafael J. Wysocki" <rafael@kernel.org>,
Abhishek Goel <huntbag@linux.vnet.ibm.com>
Cc: Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
linuxppc-dev <linuxppc-dev@lists.ozlabs.org>,
Linux PM <linux-pm@vger.kernel.org>,
"Rafael J. Wysocki" <rjw@rjwysocki.net>,
Michael Ellerman <mpe@ellerman.id.au>
Subject: Re: [PATCH 1/2] cpuidle : auto-promotion for cpuidle states
Date: Fri, 22 Mar 2019 14:26:07 +0100 [thread overview]
Message-ID: <cfb0076f-0b56-f12c-a736-469a3d11ab83@linaro.org> (raw)
In-Reply-To: <CAJZ5v0gY-theHng=bQQpw-33jHGe++iEigEM5j6Ls7vEuewuSQ@mail.gmail.com>
On 22/03/2019 10:45, Rafael J. Wysocki wrote:
> On Fri, Mar 22, 2019 at 8:31 AM Abhishek Goel
> <huntbag@linux.vnet.ibm.com> wrote:
>>
>> Currently, the cpuidle governors (menu /ladder) determine what idle state
>> an idling CPU should enter into based on heuristics that depend on the
>> idle history on that CPU. Given that no predictive heuristic is perfect,
>> there are cases where the governor predicts a shallow idle state, hoping
>> that the CPU will be busy soon. However, if no new workload is scheduled
>> on that CPU in the near future, the CPU will end up in the shallow state.
>>
>> In case of POWER, this is problematic, when the predicted state in the
>> aforementioned scenario is a lite stop state, as such lite states will
>> inhibit SMT folding, thereby depriving the other threads in the core from
>> using the core resources.
>>
>> To address this, such lite states need to be autopromoted. The cpuidle-
>> core can queue timer to correspond with the residency value of the next
>> available state. Thus leading to auto-promotion to a deeper idle state as
>> soon as possible.
>
> Isn't the tick stopping avoidance sufficient for that?
I was about to ask the same :)
--
<http://www.linaro.org/> Linaro.org │ Open source software for ARM SoCs
Follow Linaro: <http://www.facebook.com/pages/Linaro> Facebook |
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WARNING: multiple messages have this Message-ID (diff)
From: Daniel Lezcano <daniel.lezcano@linaro.org>
To: "Rafael J. Wysocki" <rafael@kernel.org>,
Abhishek Goel <huntbag@linux.vnet.ibm.com>
Cc: "Rafael J. Wysocki" <rjw@rjwysocki.net>,
linuxppc-dev <linuxppc-dev@lists.ozlabs.org>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
Linux PM <linux-pm@vger.kernel.org>
Subject: Re: [PATCH 1/2] cpuidle : auto-promotion for cpuidle states
Date: Fri, 22 Mar 2019 14:26:07 +0100 [thread overview]
Message-ID: <cfb0076f-0b56-f12c-a736-469a3d11ab83@linaro.org> (raw)
In-Reply-To: <CAJZ5v0gY-theHng=bQQpw-33jHGe++iEigEM5j6Ls7vEuewuSQ@mail.gmail.com>
On 22/03/2019 10:45, Rafael J. Wysocki wrote:
> On Fri, Mar 22, 2019 at 8:31 AM Abhishek Goel
> <huntbag@linux.vnet.ibm.com> wrote:
>>
>> Currently, the cpuidle governors (menu /ladder) determine what idle state
>> an idling CPU should enter into based on heuristics that depend on the
>> idle history on that CPU. Given that no predictive heuristic is perfect,
>> there are cases where the governor predicts a shallow idle state, hoping
>> that the CPU will be busy soon. However, if no new workload is scheduled
>> on that CPU in the near future, the CPU will end up in the shallow state.
>>
>> In case of POWER, this is problematic, when the predicted state in the
>> aforementioned scenario is a lite stop state, as such lite states will
>> inhibit SMT folding, thereby depriving the other threads in the core from
>> using the core resources.
>>
>> To address this, such lite states need to be autopromoted. The cpuidle-
>> core can queue timer to correspond with the residency value of the next
>> available state. Thus leading to auto-promotion to a deeper idle state as
>> soon as possible.
>
> Isn't the tick stopping avoidance sufficient for that?
I was about to ask the same :)
--
<http://www.linaro.org/> Linaro.org │ Open source software for ARM SoCs
Follow Linaro: <http://www.facebook.com/pages/Linaro> Facebook |
<http://twitter.com/#!/linaroorg> Twitter |
<http://www.linaro.org/linaro-blog/> Blog
next prev parent reply other threads:[~2019-03-22 13:26 UTC|newest]
Thread overview: 20+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-03-22 7:29 [PATCH 0/2] Auto-promotion logic for cpuidle states Abhishek Goel
2019-03-22 7:29 ` Abhishek Goel
2019-03-22 7:29 ` [PATCH 1/2] cpuidle : auto-promotion " Abhishek Goel
2019-03-22 7:29 ` Abhishek Goel
2019-03-22 9:45 ` Rafael J. Wysocki
2019-03-22 9:45 ` Rafael J. Wysocki
2019-03-22 13:26 ` Daniel Lezcano [this message]
2019-03-22 13:26 ` Daniel Lezcano
2019-04-01 5:11 ` Abhishek
2019-04-01 5:11 ` Abhishek
2019-04-04 10:21 ` Daniel Lezcano
2019-04-04 10:21 ` Daniel Lezcano
2019-04-04 10:54 ` Gautham R Shenoy
2019-04-04 10:54 ` Gautham R Shenoy
2019-04-04 11:10 ` Abhishek
2019-04-04 11:10 ` Abhishek
2019-03-22 7:29 ` [PATCH 2/2] cpuidle : Add auto-promotion flag to cpuidle flags Abhishek Goel
2019-03-22 7:29 ` Abhishek Goel
-- strict thread matches above, loose matches on Subject: below --
2019-03-22 6:25 [PATCH 0/2] Auto-promotion logic for cpuidle states Abhishek Goel
2019-03-22 6:25 ` [PATCH 1/2] cpuidle : auto-promotion " Abhishek Goel
2019-03-22 6:25 ` Abhishek Goel
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