From: Daniel Lezcano <daniel.lezcano@linaro.org>
To: Viresh Kumar <viresh.kumar@linaro.org>
Cc: catalin.marinas@arm.com, Rob Herring <robh+dt@kernel.org>,
Mark Rutland <mark.rutland@arm.com>,
linux-arm-kernel@lists.infradead.org,
Vincent Guittot <vincent.guittot@linaro.org>,
devicetree@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH] dt-bindings: arm: Fix cpu capacity mismatch in example
Date: Mon, 29 Oct 2018 10:26:57 +0100 [thread overview]
Message-ID: <1297c984-789f-0298-c3b8-8668f5b898de@linaro.org> (raw)
In-Reply-To: <20181029063450.3o3ay7pazik5tgne@vireshk-i7>
On 29/10/2018 07:34, Viresh Kumar wrote:
> On 26-10-18, 10:30, Daniel Lezcano wrote:
>> On 26/10/2018 06:11, Viresh Kumar wrote:
>>> On 25-10-18, 14:04, Daniel Lezcano wrote:
>>>> I think it is actually correct. The example is confusing on what the
>>>> numbers are. IIUC, it is:
>>>>
>>>> (after normalizing)
>>>>
>>>> dhrystone result on big CPU is 1024 at 1100MHz
>>>> dhrystone result on little CPU is 446 at 850MHz
>>>>
>>>> We have to scale the result of the little for 1100MHz in order to compare.
>>>>
>>>> 1100/850 = 1.294
>>>>
>>>> dhrystone result on little CPU is 446 * 1.294 = 577 at 1100MHz
>>>>
>>>> So we put the normalized values 1024 and 577. The arch_topology will
>>>> scale 577 back to 446 as it will compute the max capacity based on the
>>>> max freq which is 850MHz.
>>>>
>>>> The *final* capacities are 1024 for cluster0 and 446 for cluster1 (read
>>>> the cpu max capacity, the ones showed in the sysfs).
>>>>
>>>> Did I miss something ?
>>>
>>> No. What about making it more clear in the example to save the next idiot (like
>>> me) from wasting time :)
>>>
>>> diff --git a/Documentation/devicetree/bindings/arm/cpu-capacity.txt b/Documentation/devicetree/bindings/arm/cpu-capacity.txt
>>> index 9b5685a1d15d..d061e6575bde 100644
>>> --- a/Documentation/devicetree/bindings/arm/cpu-capacity.txt
>>> +++ b/Documentation/devicetree/bindings/arm/cpu-capacity.txt
>>> @@ -61,7 +61,10 @@ mhz values (normalized w.r.t. the highest value found while parsing the DT).
>>> Example 1 (ARM 64-bit, 6-cpu system, two clusters):
>>> capacities-dmips-mhz are scaled w.r.t. 1024 (cpu@0 and cpu@1)
>>> supposing cluster0@max-freq=1100 and custer1@max-freq=850,
>>> -final capacities are 1024 for cluster0 and 446 for cluster1
>>> +final capacities are 1024 for cluster0 and 446 for cluster1.
>>> +Note that the values mentioned below in the example (1024 and 578)
>>> +aren't normalized based on max frequency of each cluster and that is
>>> +left for the operating system to do.
>>
>> Yes, it will help but if you want to make things even more clear, I
>> suggest to elaborate the text a bit and give the numbers above to
>> explain (1100/850=1.294, 446 * 1.294 = 577, ...)
>
> I didn't wanted to explain way too much, but how about this..
>
> diff --git a/Documentation/devicetree/bindings/arm/cpu-capacity.txt b/Documentation/devicetree/bindings/arm/cpu-capacity.txt
> index 9b5685a1d15d..84262cdb8d29 100644
> --- a/Documentation/devicetree/bindings/arm/cpu-capacity.txt
> +++ b/Documentation/devicetree/bindings/arm/cpu-capacity.txt
> @@ -59,9 +59,11 @@ mhz values (normalized w.r.t. the highest value found while parsing the DT).
> ===========================================
>
> Example 1 (ARM 64-bit, 6-cpu system, two clusters):
> -capacities-dmips-mhz are scaled w.r.t. 1024 (cpu@0 and cpu@1)
> -supposing cluster0@max-freq=1100 and custer1@max-freq=850,
> -final capacities are 1024 for cluster0 and 446 for cluster1
> +The capacities-dmips-mhz or DMIPS/MHz values (scaled to 1024)
> +are 1024 and 578 for cluster0 and cluster1. Further normalization
> +is done by the operating system based on cluster0@max-freq=1100 and
> +custer1@max-freq=850, final capacities are 1024 for cluster0 and
> +446 for cluster1 (576*850/1100).
Acked-by: Daniel Lezcano <daniel.lezcano@linaro.org>
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prev parent reply other threads:[~2018-10-29 9:27 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-10-25 8:27 [PATCH] dt-bindings: arm: Fix cpu capacity mismatch in example Viresh Kumar
2018-10-25 12:04 ` Daniel Lezcano
2018-10-26 4:11 ` Viresh Kumar
2018-10-26 8:30 ` Daniel Lezcano
2018-10-29 6:34 ` Viresh Kumar
2018-10-29 9:26 ` Daniel Lezcano [this message]
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