Re: How many frequencies would cpufreq optimally like to manage?

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On 21/11/2014 04:36, Viresh Kumar wrote:

All current governors depend on background timers for their functionality.
These timers run at some sampling rate (in ms) and that time we change
CPU's frequency depending on existing load on system.. So, that might
not be fast enough.

As far as I can tell, on my SoC, the timer runs at 27 MHz.
But I have no idea how often it fires an interrupt.

I've been studying other cpufreq drivers, especially the OMAP driver.
I noticed that there is a lot of generic infrastructure that our driver
wasn't using, such as...


I've changed our driver to use those.

I'm still confused about cpufreq_generic_get.
This is not a typical get/put type function, right?

What is it supposed to get?
Apparently, the actual frequency of the 'cpu-th' CPU?
I see that it calls clk_get_rate(policy->clk)

This 'struct clk' is an elusive beast.
Where is it defined? I only run into forward declarations.

On my platform, clk_get_accuracy returns -524 unconditionally,
and clk_prepare just returns 0.

of_clk_get and of_clk_get_by_name both return ERR_PTR(-2)

I suppose all this means I can't use this infrastructure "as-is",
correct? Where can I read more about it?

How is the kernel supposed to know what frequency each core is running at?
I imagine that's what the .get method override is for?

One more question (for now). Is the .get method supposed to return numbers
that match in freq_table, or can they be slightly different? For example,
I've defined my freq_table like this:

static struct cpufreq_frequency_table freq_table[] = {
	{ .driver_data = REG_VAL(1,0), .frequency = 999000 },
	{ .driver_data = REG_VAL(1,8), .frequency = 750000 },
	{ .driver_data = REG_VAL(2,0), .frequency = 500000 },
	{ .driver_data = REG_VAL(4,0), .frequency = 250000 },
	{ .driver_data = REG_VAL(8,0), .frequency = 125000 },
	{ .frequency = CPUFREQ_TABLE_END },

but the 3rd frequency is actually 999/2 MHz, not 500 MHz, etc.
Will that be a problem?


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