[PATCH v7 3/6] cpufreq: powernv: Remove cpu_to_chip_id() from hot-path

Shilpasri G Bhat
2016-01-28T07:27:12Z

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 <anton@samba.org>
Signed-off-by: Shilpasri G Bhat <shilpa.bhat@linux.vnet.ibm.com>
---
Changes from v6:
- Minor changes to move the code 'cpumask_copy()' after 'core_to_chip_map'
is allocated.
- Move 'kfree(chips)' to a separate patch.

No changes from v5.

Changes from v4:
- Taken care of Shreyas's comments to add a core_to_chip_map array to
store the chip id.

drivers/cpufreq/powernv-cpufreq.c | 23 ++++++++++++++++++++---
1 file changed, 20 insertions(+), 3 deletions(-)

diff --git a/drivers/cpufreq/powernv-cpufreq.c b/drivers/cpufreq/powernv-cpufreq.c
index a271b0f..c670314 100644
--- a/drivers/cpufreq/powernv-cpufreq.c
+++ b/drivers/cpufreq/powernv-cpufreq.c
@@ -43,6 +43,7 @@

static struct cpufreq_frequency_table powernv_freqs[POWERNV_MAX_PSTATES+1];
static bool rebooting, throttled, occ_reset;
+static unsigned int *core_to_chip_map;

static struct chip {
unsigned int id;
@@ -313,13 +314,14 @@ static inline unsigned int get_nominal_index(void)
static void powernv_cpufreq_throttle_check(void *data)
{
unsigned int cpu = smp_processor_id();
+ unsigned int chip_id = core_to_chip_map[cpu_core_index_of_thread(cpu)];
unsigned long pmsr;
int pmsr_pmax, i;

pmsr = get_pmspr(SPRN_PMSR);

for (i = 0; i < nr_chips; i++)
- if (chips[i].id == cpu_to_chip_id(cpu))
+ if (chips[i].id == chip_id)
break;

/* Check for Pmax Capping */
@@ -559,19 +561,29 @@ static int init_chip_info(void)
unsigned int chip[256];
unsigned int cpu, i;
unsigned int prev_chip_id = UINT_MAX;
+ cpumask_t cpu_mask;
+ int ret = -ENOMEM;

- for_each_possible_cpu(cpu) {
+ core_to_chip_map = kcalloc(cpu_nr_cores(), sizeof(unsigned int),
+ GFP_KERNEL);
+ if (!core_to_chip_map)
+ goto out;
+
+ cpumask_copy(&cpu_mask, cpu_possible_mask);
+ for_each_cpu(cpu, &cpu_mask) {
unsigned int id = cpu_to_chip_id(cpu);

if (prev_chip_id != id) {
prev_chip_id = id;
chip[nr_chips++] = id;
}
+ core_to_chip_map[cpu_core_index_of_thread(cpu)] = id;
+ cpumask_andnot(&cpu_mask, &cpu_mask, cpu_sibling_mask(cpu));
}

chips = kmalloc_array(nr_chips, sizeof(struct chip), GFP_KERNEL);
if (!chips)
- return -ENOMEM;
+ goto free_chip_map;

for (i = 0; i < nr_chips; i++) {
chips[i].id = chip[i];
@@ -582,6 +594,10 @@ static int init_chip_info(void)
}

return 0;
+free_chip_map:
+ kfree(core_to_chip_map);
+out:
+ return ret;
}

static int __init powernv_cpufreq_init(void)
@@ -616,6 +632,7 @@ static void __exit powernv_cpufreq_exit(void)
opal_message_notifier_unregister(OPAL_MSG_OCC,
&powernv_cpufreq_opal_nb);
kfree(chips);
+ kfree(core_to_chip_map);
cpufreq_unregister_driver(&powernv_cpufreq_driver);
}
module_exit(powernv_cpufreq_exit);
--
1.9.3