linux-kernel - Re: [PATCH v1] arch_topology: Adjust initial CPU capacities with current freq

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Date:   Fri, 10 Jan 2020 13:01:24 +0100
From:   Dietmar Eggemann <dietmar.eggemann@....com>
To:     Sudeep Holla <sudeep.holla@....com>,
        Jeffy Chen <jeffy.chen@...k-chips.com>
Cc:     linux-kernel@...r.kernel.org,
        Brian Norris <briannorris@...omium.org>,
        Marc Zyngier <marc.zyngier@....com>,
        Douglas Anderson <dianders@...omium.org>,
        Robin Murphy <robin.murphy@....com>,
        Heiko Stuebner <heiko@...ech.de>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "Rafael J. Wysocki" <rafael@...nel.org>
Subject: Re: [PATCH v1] arch_topology: Adjust initial CPU capacities with
 current freq

On 10/01/2020 12:37, Sudeep Holla wrote:
> On Thu, Jan 09, 2020 at 03:52:14PM +0800, Jeffy Chen wrote:
>> The CPU freqs are not supposed to change before cpufreq policies
>> properly registered, meaning that they should be used to calculate the
>> initial CPU capacities.
>>
>> Doing this helps choosing the best CPU during early boot, especially
>> for the initramfs decompressing.
>>
>> Signed-off-by: Jeffy Chen <jeffy.chen@...k-chips.com>
> 
> [...]
> 
>> @@ -146,10 +153,15 @@ bool __init topology_parse_cpu_capacity(struct device_node *cpu_node, int cpu)
>>  				return false;
>>  			}
>>  		}
>> -		capacity_scale = max(cpu_capacity, capacity_scale);
>>  		raw_capacity[cpu] = cpu_capacity;
>>  		pr_debug("cpu_capacity: %pOF cpu_capacity=%u (raw)\n",
>>  			cpu_node, raw_capacity[cpu]);
>> +
>> +		cpu_clk = of_clk_get(cpu_node, 0);
>> +		if (!PTR_ERR_OR_ZERO(cpu_clk))
>> +			per_cpu(max_freq, cpu) = clk_get_rate(cpu_clk) / 1000;
>> +
>> +		clk_put(cpu_clk);
> 
> I don't like to assume DVFS to be supplied only using 'clk'. So NACK!
> We have other non-clk mechanism for CPU DVFS and this needs to simply
> use cpufreq APIs to get frequency value if required.

To support this, it's failing on my Arm64 Juno board.

...
[    0.084858] CPU1 cpu_clk=-517
[    0.087961] CPU2 cpu_clk=-517
[    0.091005] CPU0 cpu_clk=-517
[    0.094121] CPU3 cpu_clk=-517
[    0.097248] CPU4 cpu_clk=-517
[    0.100415] CPU5 cpu_clk=-517
...

Since you're on a big.LITTLE platform, did you specify
'capacity-dmips-mhz' for CPUs to be able to distinguish big and little
CPUs before CPUfreq kicks in?

$ grep capacity-dmips-mhz ./arch/arm64/boot/dts/arm/juno.dts
			capacity-dmips-mhz = <1024>;
			capacity-dmips-mhz = <1024>;
			capacity-dmips-mhz = <578>;
			capacity-dmips-mhz = <578>;
			capacity-dmips-mhz = <578>;
			capacity-dmips-mhz = <578>;