Re: [PATCH RESEND v4 1/4] cpufreq: powernv: Remove cpu_to_chip_id() from hot-path
From: Shreyas B Prabhu <hidden>
Date: 2016-01-12 10:58:01
Also in:
linux-pm, lkml
On 01/12/2016 03:54 PM, Shilpasri G Bhat wrote:
quoted hunk ↗ jump to hunk
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 cpu_to_chip_id() use PIR of the cpu to find the chip id. Reported-by: Anton Blanchard <redacted> Signed-off-by: Shilpasri G Bhat <redacted> --- drivers/cpufreq/powernv-cpufreq.c | 7 +++++-- 1 file changed, 5 insertions(+), 2 deletions(-)diff --git a/drivers/cpufreq/powernv-cpufreq.c b/drivers/cpufreq/powernv-cpufreq.c index cb50138..597a084 100644 --- a/drivers/cpufreq/powernv-cpufreq.c +++ b/drivers/cpufreq/powernv-cpufreq.c@@ -39,6 +39,7 @@ #define PMSR_PSAFE_ENABLE (1UL << 30) #define PMSR_SPR_EM_DISABLE (1UL << 31) #define PMSR_MAX(x) ((x >> 32) & 0xFF) +#define pir_to_chip_id(pir) (((pir) >> 7) & 0x3f)
Since this is platform specific and true only for power8, this is not the right place to put it. Either you can move this to arch/powerpc or you can maintain a cpu to chip map within the driver.
quoted hunk ↗ jump to hunk
static struct cpufreq_frequency_table powernv_freqs[POWERNV_MAX_PSTATES+1]; static bool rebooting, throttled, occ_reset;@@ -312,13 +313,14 @@ 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 = pir_to_chip_id(hard_smp_processor_id()); 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 */@@ -558,7 +560,8 @@ static int init_chip_info(void) unsigned int prev_chip_id = UINT_MAX; for_each_possible_cpu(cpu) { - unsigned int id = cpu_to_chip_id(cpu); + unsigned int id = + pir_to_chip_id(get_hard_smp_processor_id(cpu)); if (prev_chip_id != id) { prev_chip_id = id;
Thanks, Shreyas