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From: Daniel Lezcano <daniel.lezcano@linaro.org>
To: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
Cc: Viresh Kumar <viresh.kumar@linaro.org>,
	Sudeep Holla <sudeep.holla@arm.com>,
	edubezval@gmail.com, kevin.wangtao@linaro.org,
	leo.yan@linaro.org, vincent.guittot@linaro.org,
	linux-kernel@vger.kernel.org, javi.merino@kernel.org,
	rui.zhang@intel.com, daniel.thompson@linaro.org,
	linux-pm@vger.kernel.org,
	Amit Daniel Kachhap <amit.kachhap@gmail.com>
Subject: Re: [PATCH v3 6/7] thermal/drivers/cpu_cooling: Introduce the cpu idle cooling driver
Date: Tue, 17 Apr 2018 09:17:36 +0200	[thread overview]
Message-ID: <845fafa3-f0ab-2050-fe32-1780dc61b8a8@linaro.org> (raw)
In-Reply-To: <20180416142243.GB32565@red-moon>

On 16/04/2018 16:22, Lorenzo Pieralisi wrote:
> On Mon, Apr 16, 2018 at 03:57:03PM +0200, Daniel Lezcano wrote:
>> On 16/04/2018 14:30, Lorenzo Pieralisi wrote:
>>> On Mon, Apr 16, 2018 at 02:10:30PM +0200, Daniel Lezcano wrote:
>>>> On 16/04/2018 12:10, Viresh Kumar wrote:
>>>>> On 16-04-18, 12:03, Daniel Lezcano wrote:
>>>>>> On 16/04/2018 11:50, Viresh Kumar wrote:
>>>>>>> On 16-04-18, 11:45, Daniel Lezcano wrote:
>>>>>>>> Can you elaborate a bit ? I'm not sure to get the point.
>>>>>>>
>>>>>>> Sure. With your current code on Hikey960 (big/LITTLE), you end up
>>>>>>> creating two cooling devices, one for the big cluster and one for
>>>>>>> small cluster. Which is the right thing to do, as we also have two
>>>>>>> cpufreq cooling devices.
>>>>>>>
>>>>>>> But with the change Sudeep is referring to, the helper you used to get
>>>>>>> cluster id will return 0 (SoC id) for all the 8 CPUs. So your code
>>>>>>> will end up creating a single cpuidle cooling device for all the CPUs.
>>>>>>> Which would be wrong.
>>>>>>
>>>>>> Is the semantic of topology_physical_package_id changing ?
>>>>>
>>>>> That's what I understood from his email.
>>>>>
>>>>>> I don't
>>>>>> understand the change Sudeep is referring to.
>>>>
>>>> Actually there is no impact with the change Sudeep is referring to. It
>>>> is for ACPI, we are DT based. Confirmed with Jeremy.
>>>>
>>>> So AFAICT, it is not a problem.
>>>
>>> It is a problem - DT or ACPI alike. Sudeep was referring to the notion
>>> of "cluster" that has no architectural meaning whatsoever and using
>>> topology_physical_package_id() to detect a "cluster" was/is/will always
>>> be the wrong thing to do. The notion of cluster must not appear in the
>>> kernel at all, it has no architectural meaning. I understand you need
>>> to group CPUs but that has to be done in a different way, through
>>> cooling devices, thermal domains or power domains DT/ACPI bindings but
>>> not by using topology masks.
>>
>> I don't get it. What is the cluster concept defined in the ARM
>> documentation?
>>
>> ARM Cortex-A53 MPCore Processor Technical Reference Manual
>>
>> 4.5.2. Multiprocessor Affinity Register
>>
>> I see the documentation says:
>>
>> A cluster with two cores, three cores, ...
>>
>> How the kernel can represent that if you kill the
>> topology_physical_package_id() ?
> 
> From an Arm ARM perspective (ARM v8 reference manual), the MPIDR_EL1 has
> no notion of cluster which means that a cluster is not architecturally
> defined on Arm systems.

Sorry, I'm lost :/ You say the MPIDR_EL1 has no notion of cluster but
the documentation describing this register is all talking about cluster.

http://infocenter.arm.com/help/index.jsp?topic=/com.arm.doc.ddi0500g/BABHBJCI.html

> Currently, as Morten explained today, topology_physical_package_id()
> is supposed to represent a "cluster" and that's completely wrong
> because a "cluster" cannot be defined from an architectural perspective.
> 
> It was a bodge used as a shortcut, wrongly. We should have never used
> that API for that purpose and there must be no code in the kernel
> relying on:
> 
> topology_physical_package_id()
> 
> to define a cluster; the information you require to group CPUs must
> come from something else, which is firmware bindings(DT or ACPI) as
> I mentioned.

Why not ?

diff --git a/arch/arm64/include/asm/topology.h
b/arch/arm64/include/asm/topology.h
index c4f2d50..ac0776d 100644
--- a/arch/arm64/include/asm/topology.h
+++ b/arch/arm64/include/asm/topology.h
@@ -14,7 +14,8 @@ struct cpu_topology {

 extern struct cpu_topology cpu_topology[NR_CPUS];

-#define topology_physical_package_id(cpu)
(cpu_topology[cpu].cluster_id)
+#define topology_physical_package_id(cpu)      (0)
+#define topology_physical_cluster_id(cpu)
(cpu_topology[cpu].cluster_id)
 #define topology_core_id(cpu)          (cpu_topology[cpu].core_id)
 #define topology_core_cpumask(cpu)     (&cpu_topology[cpu].core_sibling)
 #define topology_sibling_cpumask(cpu)  (&cpu_topology[cpu].thread_sibling)


> Please speak to Sudeep who will fill you on the reasoning above.

Yes, Sudeep is next to me but I would prefer to keep the discussion on
the mailing list so everyone can get the reasoning.



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  reply	other threads:[~2018-04-17  7:17 UTC|newest]

Thread overview: 46+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-04-05 16:16 [PATCH v3 0/7] CPU cooling device new strategies Daniel Lezcano
2018-04-05 16:16 ` [PATCH v3 1/7] thermal/drivers/cpu_cooling: Fixup the header and copyright Daniel Lezcano
     [not found]   ` <20180411061514.GL7671@vireshk-i7>
2018-04-11  8:56     ` Daniel Lezcano
2018-04-05 16:16 ` [PATCH v3 2/7] thermal/drivers/cpu_cooling: Add Software Package Data Exchange (SPDX) Daniel Lezcano
2018-04-05 16:16 ` [PATCH v3 3/7] thermal/drivers/cpu_cooling: Remove pointless field Daniel Lezcano
2018-04-05 16:16 ` [PATCH v3 4/7] thermal/drivers/Kconfig: Convert the CPU cooling device to a choice Daniel Lezcano
     [not found]   ` <20180411061851.GM7671@vireshk-i7>
2018-04-11  8:58     ` Daniel Lezcano
2018-04-05 16:16 ` [PATCH v3 5/7] thermal/drivers/cpu_cooling: Add idle cooling device documentation Daniel Lezcano
2018-04-05 16:16 ` [PATCH v3 6/7] thermal/drivers/cpu_cooling: Introduce the cpu idle cooling driver Daniel Lezcano
2018-04-11  8:51   ` Viresh Kumar
2018-04-11  9:29     ` Daniel Lezcano
2018-04-13 11:23   ` Sudeep Holla
2018-04-13 11:47     ` Daniel Lezcano
2018-04-16  7:37       ` Viresh Kumar
2018-04-16  7:44         ` Daniel Lezcano
2018-04-16  9:34           ` Sudeep Holla
2018-04-16  9:37           ` Viresh Kumar
2018-04-16  9:45             ` Daniel Lezcano
2018-04-16  9:50               ` Viresh Kumar
2018-04-16 10:03                 ` Daniel Lezcano
2018-04-16 10:10                   ` Viresh Kumar
2018-04-16 12:10                     ` Daniel Lezcano
2018-04-16 12:30                       ` Lorenzo Pieralisi
2018-04-16 13:57                         ` Daniel Lezcano
2018-04-16 14:22                           ` Lorenzo Pieralisi
2018-04-17  7:17                             ` Daniel Lezcano [this message]
2018-04-17 10:24                               ` Lorenzo Pieralisi
2018-04-16 12:31                       ` Sudeep Holla
2018-04-16 12:49                         ` Daniel Lezcano
2018-04-16 13:03                           ` Sudeep Holla
2018-04-16 12:29                 ` Sudeep Holla
2018-04-13 11:38   ` Daniel Thompson
2018-04-13 11:46     ` Daniel Lezcano
2019-08-05  5:11   ` Martin Kepplinger
2019-08-05  6:53     ` Martin Kepplinger
2019-08-05  7:39       ` Daniel Lezcano
2019-08-05  7:42         ` Martin Kepplinger
2019-08-05  7:58           ` Daniel Lezcano
2019-10-25 11:22             ` Martin Kepplinger
2019-10-25 14:45               ` Daniel Lezcano
2019-10-26 18:23                 ` Martin Kepplinger
2019-10-28 15:16                   ` Daniel Lezcano
2019-08-05  7:37     ` Daniel Lezcano
2019-08-05  7:40       ` Martin Kepplinger
2018-04-05 16:16 ` [PATCH v3 7/7] cpuidle/drivers/cpuidle-arm: Register the cooling device Daniel Lezcano
2018-04-11  8:51   ` Viresh Kumar

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