Re: [PATCH v8 3/6] cpufreq: powernv: Remove cpu_to_chip_id() from hot-path

On Fri, 2016-03-18 at 15:04 +1100, Michael Neuling wrote:

On Wed, 2016-02-03 at 01:11 +0530, Shilpasri G Bhat wrote:
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quoted

cpu_to_chip_id() does a DT walk through to find out the chip id by
taking a contended device tree lock. This adds an unnecessary
overhead
in a hot path. So instead of calling cpu_to_chip_id() everytime
cache
the chip ids for all cores in the array 'core_to_chip_map' and use
it
in the hotpath.
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Reported-by: Anton Blanchard <redacted>
Signed-off-by: Shilpasri G Bhat <redacted>
Reviewed-by: Gautham R. Shenoy <redacted>
Acked-by: Viresh Kumar <viresh.kumar@linaro.org>
---
No changes from v7.

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How about this instead?  It removes the linear lookup and seems a lot
less complex.

BTW we never init nr_chips before using it.  We also need something
like.

diff --git a/drivers/cpufreq/powernv-cpufreq.c b/drivers/cpufreq/powernv-cp=

ufreq.c
index d63d2cb..c819ed4 100644

--- a/drivers/cpufreq/powernv-cpufreq.c
+++ b/drivers/cpufreq/powernv-cpufreq.c

@@ -556,6 +556,8 @@ static int init_chip_info(void)
 	unsigned int cpu, i;
 	unsigned int prev_chip_id =3D UINT_MAX;

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+	nr_chips =3D 0;
+
 	for_each_possible_cpu(cpu) {
 		unsigned int id =3D cpu_to_chip_id(cpu);
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