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