From 988ce13db9fdacf3b8b9e4fa2a77d186d50a157e Mon Sep 17 00:00:00 2001 From: Dimitri Sivanich Date: Thu, 8 Dec 2011 15:32:13 +1100 Subject: [PATCH] tick-sched: add specific do_timer_cpu value for nohz off mode Show and modify the tick_do_timer_cpu via sysfs. This determines the cpu on which global time (jiffies) updates occur. Modification can only be done on systems with nohz mode turned off. While not necessarily harmful, doing jiffies updates on an application cpu does cause some extra overhead that HPC benchmarking people notice. They prefer to have OS activity isolated to certain cpus. They like reproducibility of results, and having jiffies updates bouncing around introduces variability. Signed-off-by: Dimitri Sivanich Cc: John Stultz Cc: Thomas Gleixner Signed-off-by: Andrew Morton --- .../testing/sysfs-devices-system-timekeeping | 16 +++++ drivers/base/sys.c | 10 ++- include/linux/sysdev.h | 2 + kernel/time/tick-sched.c | 67 +++++++++++++++++++ 4 files changed, 89 insertions(+), 6 deletions(-) create mode 100644 Documentation/ABI/testing/sysfs-devices-system-timekeeping diff --git a/Documentation/ABI/testing/sysfs-devices-system-timekeeping b/Documentation/ABI/testing/sysfs-devices-system-timekeeping new file mode 100644 index 000000000000..a904c6da25e5 --- /dev/null +++ b/Documentation/ABI/testing/sysfs-devices-system-timekeeping @@ -0,0 +1,16 @@ +What: /sys/devices/system/timekeeping/ +Date: November 2011 +Contact: Linux kernel mailing list +Description: Timekeeping attributes + + +What: /sys/devices/system/timekeeping/timekeeping0/jiffies_cpu +Date: November 2011 +Contact: Linux kernel mailing list +Description: Show and modify the kernel's tick_do_timer_cpu. This + determines the cpu on which global time (jiffies) updates + occur. This can only be modified on systems running with + the nohz mode turned off (nohz=off). + + Possible values are: + 0 - diff --git a/drivers/base/sys.c b/drivers/base/sys.c index 9dff77bfe1e3..67d81a228d43 100644 --- a/drivers/base/sys.c +++ b/drivers/base/sys.c @@ -339,13 +339,11 @@ int __init system_bus_init(void) return 0; } -#define to_ext_attr(x) container_of(x, struct sysdev_ext_attribute, attr) - ssize_t sysdev_store_ulong(struct sys_device *sysdev, struct sysdev_attribute *attr, const char *buf, size_t size) { - struct sysdev_ext_attribute *ea = to_ext_attr(attr); + struct sysdev_ext_attribute *ea = SYSDEV_TO_EXT_ATTR(attr); char *end; unsigned long new = simple_strtoul(buf, &end, 0); if (end == buf) @@ -360,7 +358,7 @@ ssize_t sysdev_show_ulong(struct sys_device *sysdev, struct sysdev_attribute *attr, char *buf) { - struct sysdev_ext_attribute *ea = to_ext_attr(attr); + struct sysdev_ext_attribute *ea = SYSDEV_TO_EXT_ATTR(attr); return snprintf(buf, PAGE_SIZE, "%lx\n", *(unsigned long *)(ea->var)); } EXPORT_SYMBOL_GPL(sysdev_show_ulong); @@ -369,7 +367,7 @@ ssize_t sysdev_store_int(struct sys_device *sysdev, struct sysdev_attribute *attr, const char *buf, size_t size) { - struct sysdev_ext_attribute *ea = to_ext_attr(attr); + struct sysdev_ext_attribute *ea = SYSDEV_TO_EXT_ATTR(attr); char *end; long new = simple_strtol(buf, &end, 0); if (end == buf || new > INT_MAX || new < INT_MIN) @@ -384,7 +382,7 @@ ssize_t sysdev_show_int(struct sys_device *sysdev, struct sysdev_attribute *attr, char *buf) { - struct sysdev_ext_attribute *ea = to_ext_attr(attr); + struct sysdev_ext_attribute *ea = SYSDEV_TO_EXT_ATTR(attr); return snprintf(buf, PAGE_SIZE, "%d\n", *(int *)(ea->var)); } EXPORT_SYMBOL_GPL(sysdev_show_int); diff --git a/include/linux/sysdev.h b/include/linux/sysdev.h index 20f63d3e6144..7ab0c81cab1d 100644 --- a/include/linux/sysdev.h +++ b/include/linux/sysdev.h @@ -132,6 +132,8 @@ struct sysdev_ext_attribute { void *var; }; +#define SYSDEV_TO_EXT_ATTR(x) container_of(x, struct sysdev_ext_attribute, attr) + /* * Support for simple variable sysdev attributes. * The pointer to the variable is stored in a sysdev_ext_attribute diff --git a/kernel/time/tick-sched.c b/kernel/time/tick-sched.c index 31cc06163ed5..8fb8d6e4a031 100644 --- a/kernel/time/tick-sched.c +++ b/kernel/time/tick-sched.c @@ -843,6 +843,73 @@ void tick_cancel_sched_timer(int cpu) } #endif +#ifdef CONFIG_SYSFS +/* + * Allow modification of tick_do_timer_cpu when nohz mode is off. + */ +static ssize_t sysfs_store_do_timer_cpu(struct sys_device *dev, + struct sysdev_attribute *attr, + const char *buf, size_t size) +{ + struct sysdev_ext_attribute *ea = SYSDEV_TO_EXT_ATTR(attr); + unsigned int new; + int rv; + +#ifdef CONFIG_NO_HZ + /* nohz mode not supported */ + if (tick_nohz_enabled) + return -EINVAL; +#endif + + rv = kstrtouint(buf, 0, &new); + if (rv) + return rv; + + /* Protect against cpu-hotplug */ + get_online_cpus(); + + if (new >= nr_cpu_ids || !cpu_online(new)) { + put_online_cpus(); + return -ERANGE; + } + + *(unsigned int *)(ea->var) = new; + + put_online_cpus(); + + return size; +} + +static struct sysdev_ext_attribute attr_jiffies_cpu = { + _SYSDEV_ATTR(jiffies_cpu, 0644, sysdev_show_int, + sysfs_store_do_timer_cpu), + &tick_do_timer_cpu }; + +static struct sysdev_class timekeeping_sysclass = { + .name = "timekeeping", +}; + +static struct sys_device device_timekeeping = { + .id = 0, + .cls = &timekeeping_sysclass, +}; + +static int __init init_timekeeping_sysfs(void) +{ + int error = sysdev_class_register(&timekeeping_sysclass); + + if (!error) + error = sysdev_register(&device_timekeeping); + if (!error) + error = sysdev_create_file( + &device_timekeeping, + &attr_jiffies_cpu.attr); + return error; +} + +device_initcall(init_timekeeping_sysfs); +#endif /* SYSFS */ + /** * Async notification about clocksource changes */ -- 2.39.5