On Wed, 2016-02-03 at 01:11 +0530, Shilpasri G Bhat wrote:
> 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.
>
> Reported-by: Anton Blanchard <an...@samba.org>
> Signed-off-by: Shilpasri G Bhat <shilpa.b...@linux.vnet.ibm.com>
> Reviewed-by: Gautham R. Shenoy <e...@linux.vnet.ibm.com>
> Acked-by: Viresh Kumar <viresh.ku...@linaro.org>
> ---
> No changes from v7.
How about this instead? It removes the linear lookup and seems a lot
less complex.
Mikey
diff --git a/drivers/cpufreq/powernv-cpufreq.c
b/drivers/cpufreq/powernv-cpufreq.c
index 547890f..d63d2cb 100644
--- a/drivers/cpufreq/powernv-cpufreq.c
+++ b/drivers/cpufreq/powernv-cpufreq.c
@@ -52,6 +52,7 @@ static struct chip {
} *chips;
static int nr_chips;
+static DEFINE_PER_CPU(unsigned int, chip_id);
/*
* Note: The set of pstates consists of contiguous integers, the
@@ -317,9 +318,7 @@ static void powernv_cpufreq_throttle_check(void *data)
pmsr = get_pmspr(SPRN_PMSR);
- for (i = 0; i < nr_chips; i++)
- if (chips[i].id == cpu_to_chip_id(cpu))
- break;
+ i = this_cpu_read(chip_id);
/* Check for Pmax Capping */
pmsr_pmax = (s8)PMSR_MAX(pmsr);
@@ -560,6 +559,7 @@ static int init_chip_info(void)
for_each_possible_cpu(cpu) {
unsigned int id = cpu_to_chip_id(cpu);
+ per_cpu(chip_id, cpu) = nr_chips;
if (prev_chip_id != id) {
prev_chip_id = id;
chip[nr_chips++] = id;
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