From b878dc00595440586874952dd85ce9b803360b87 Mon Sep 17 00:00:00 2001 From: Anton Blanchard Date: Sun, 16 May 2010 20:02:39 +0000 Subject: [PATCH] powerpc: Use smt_snooze_delay=-1 to always busy loop Right now if we want to busy loop and not give up any time to the hypervisor we put a very large value into smt_snooze_delay. This is sometimes useful when running a single partition and you want to avoid any latencies due to the hypervisor or CPU power state transitions. While this works, it's a bit ugly - how big a number is enough now we have NO_HZ and can be idle for a very long time. The patch below makes smt_snooze_delay signed, and a negative value means loop forever: echo -1 > /sys/devices/system/cpu/cpu0/smt_snooze_delay This change shouldn't affect the existing userspace tools (eg ppc64_cpu), but I'm cc-ing Nathan just to be sure. Signed-off-by: Anton Blanchard Signed-off-by: Benjamin Herrenschmidt --- arch/powerpc/kernel/sysfs.c | 17 ++++++++--------- arch/powerpc/platforms/pseries/setup.c | 10 +++++----- 2 files changed, 13 insertions(+), 14 deletions(-) diff --git a/arch/powerpc/kernel/sysfs.c b/arch/powerpc/kernel/sysfs.c index 158fb731e199..c0d8c2006bf4 100644 --- a/arch/powerpc/kernel/sysfs.c +++ b/arch/powerpc/kernel/sysfs.c @@ -35,7 +35,7 @@ static DEFINE_PER_CPU(struct cpu, cpu_devices); #ifdef CONFIG_PPC64 /* Time in microseconds we delay before sleeping in the idle loop */ -DEFINE_PER_CPU(unsigned long, smt_snooze_delay) = { 100 }; +DEFINE_PER_CPU(long, smt_snooze_delay) = { 100 }; static ssize_t store_smt_snooze_delay(struct sys_device *dev, struct sysdev_attribute *attr, @@ -44,9 +44,9 @@ static ssize_t store_smt_snooze_delay(struct sys_device *dev, { struct cpu *cpu = container_of(dev, struct cpu, sysdev); ssize_t ret; - unsigned long snooze; + long snooze; - ret = sscanf(buf, "%lu", &snooze); + ret = sscanf(buf, "%ld", &snooze); if (ret != 1) return -EINVAL; @@ -61,7 +61,7 @@ static ssize_t show_smt_snooze_delay(struct sys_device *dev, { struct cpu *cpu = container_of(dev, struct cpu, sysdev); - return sprintf(buf, "%lu\n", per_cpu(smt_snooze_delay, cpu->sysdev.id)); + return sprintf(buf, "%ld\n", per_cpu(smt_snooze_delay, cpu->sysdev.id)); } static SYSDEV_ATTR(smt_snooze_delay, 0644, show_smt_snooze_delay, @@ -70,15 +70,14 @@ static SYSDEV_ATTR(smt_snooze_delay, 0644, show_smt_snooze_delay, static int __init setup_smt_snooze_delay(char *str) { unsigned int cpu; - int snooze; + long snooze; if (!cpu_has_feature(CPU_FTR_SMT)) return 1; - if (get_option(&str, &snooze)) { - for_each_possible_cpu(cpu) - per_cpu(smt_snooze_delay, cpu) = snooze; - } + snooze = simple_strtol(str, NULL, 10); + for_each_possible_cpu(cpu) + per_cpu(smt_snooze_delay, cpu) = snooze; return 1; } diff --git a/arch/powerpc/platforms/pseries/setup.c b/arch/powerpc/platforms/pseries/setup.c index 6710761bf60f..a6d19e3a505e 100644 --- a/arch/powerpc/platforms/pseries/setup.c +++ b/arch/powerpc/platforms/pseries/setup.c @@ -496,13 +496,14 @@ static int __init pSeries_probe(void) } -DECLARE_PER_CPU(unsigned long, smt_snooze_delay); +DECLARE_PER_CPU(long, smt_snooze_delay); static void pseries_dedicated_idle_sleep(void) { unsigned int cpu = smp_processor_id(); unsigned long start_snooze; unsigned long in_purr, out_purr; + long snooze = __get_cpu_var(smt_snooze_delay); /* * Indicate to the HV that we are idle. Now would be @@ -517,13 +518,12 @@ static void pseries_dedicated_idle_sleep(void) * has been checked recently. If we should poll for a little * while, do so. */ - if (__get_cpu_var(smt_snooze_delay)) { - start_snooze = get_tb() + - __get_cpu_var(smt_snooze_delay) * tb_ticks_per_usec; + if (snooze) { + start_snooze = get_tb() + snooze * tb_ticks_per_usec; local_irq_enable(); set_thread_flag(TIF_POLLING_NRFLAG); - while (get_tb() < start_snooze) { + while ((snooze < 0) || (get_tb() < start_snooze)) { if (need_resched() || cpu_is_offline(cpu)) goto out; ppc64_runlatch_off(); -- 2.20.1