Change the default behavior of watchdog so it only runs on the housekeeping cores when nohz_full is enabled at build and boot time.
Allow modifying the set of cores the watchdog is currently running on with a new kernel.watchdog_cpumask sysctl. Acked-by: Don Zickus <[email protected]> Signed-off-by: Chris Metcalf <[email protected]> --- Documentation/lockup-watchdogs.txt | 6 ++++++ Documentation/sysctl/kernel.txt | 11 ++++++++++ include/linux/nmi.h | 3 +++ kernel/sysctl.c | 7 ++++++ kernel/watchdog.c | 44 ++++++++++++++++++++++++++++++++++++++ 5 files changed, 71 insertions(+) diff --git a/Documentation/lockup-watchdogs.txt b/Documentation/lockup-watchdogs.txt index ab0baa692c13..31c312853d4c 100644 --- a/Documentation/lockup-watchdogs.txt +++ b/Documentation/lockup-watchdogs.txt @@ -61,3 +61,9 @@ As explained above, a kernel knob is provided that allows administrators to configure the period of the hrtimer and the perf event. The right value for a particular environment is a trade-off between fast response to lockups and detection overhead. + +By default, the watchdog runs on all online cores. However, on a +kernel configured with NO_HZ_FULL, by default the watchdog runs only +on the housekeeping cores, not the cores specified in the "nohz_full" +boot argument. In either case, the set of cores excluded from running +the watchdog may be adjusted via the kernel.watchdog_cpumask sysctl. diff --git a/Documentation/sysctl/kernel.txt b/Documentation/sysctl/kernel.txt index c831001c45f1..f6a9dca8c100 100644 --- a/Documentation/sysctl/kernel.txt +++ b/Documentation/sysctl/kernel.txt @@ -923,6 +923,17 @@ and nmi_watchdog. ============================================================== +watchdog_cpumask: + +This value can be used to control on which cpus the watchdog may run. +The default cpumask is all possible cores, but if NO_HZ_FULL is +enabled in the kernel config, and cores are specified with the +nohz_full= boot argument, those cores are excluded by default. +Offline cores can be included in this mask, and if the core is later +brought online, the watchdog will be started based on the mask value. + +============================================================== + watchdog_thresh: This value can be used to control the frequency of hrtimer and NMI diff --git a/include/linux/nmi.h b/include/linux/nmi.h index 3d46fb4708e0..f94da0e65dea 100644 --- a/include/linux/nmi.h +++ b/include/linux/nmi.h @@ -67,6 +67,7 @@ extern int nmi_watchdog_enabled; extern int soft_watchdog_enabled; extern int watchdog_user_enabled; extern int watchdog_thresh; +extern unsigned long *watchdog_cpumask_bits; extern int sysctl_softlockup_all_cpu_backtrace; struct ctl_table; extern int proc_watchdog(struct ctl_table *, int , @@ -77,6 +78,8 @@ extern int proc_soft_watchdog(struct ctl_table *, int , void __user *, size_t *, loff_t *); extern int proc_watchdog_thresh(struct ctl_table *, int , void __user *, size_t *, loff_t *); +extern int proc_watchdog_cpumask(struct ctl_table *, int, + void __user *, size_t *, loff_t *); #endif #ifdef CONFIG_HAVE_ACPI_APEI_NMI diff --git a/kernel/sysctl.c b/kernel/sysctl.c index 2082b1a88fb9..699571a74e3b 100644 --- a/kernel/sysctl.c +++ b/kernel/sysctl.c @@ -881,6 +881,13 @@ static struct ctl_table kern_table[] = { .extra2 = &one, }, { + .procname = "watchdog_cpumask", + .data = &watchdog_cpumask_bits, + .maxlen = NR_CPUS, + .mode = 0644, + .proc_handler = proc_watchdog_cpumask, + }, + { .procname = "softlockup_panic", .data = &softlockup_panic, .maxlen = sizeof(int), diff --git a/kernel/watchdog.c b/kernel/watchdog.c index 2316f50b07a4..2199f1f0b5a5 100644 --- a/kernel/watchdog.c +++ b/kernel/watchdog.c @@ -19,6 +19,7 @@ #include <linux/sysctl.h> #include <linux/smpboot.h> #include <linux/sched/rt.h> +#include <linux/tick.h> #include <asm/irq_regs.h> #include <linux/kvm_para.h> @@ -56,6 +57,8 @@ int __read_mostly sysctl_softlockup_all_cpu_backtrace; #else #define sysctl_softlockup_all_cpu_backtrace 0 #endif +static cpumask_var_t watchdog_cpumask; +unsigned long *watchdog_cpumask_bits; static int __read_mostly watchdog_running; static u64 __read_mostly sample_period; @@ -869,12 +872,53 @@ out: mutex_unlock(&watchdog_proc_mutex); return err; } + +/* + * The cpumask is the mask of possible cpus that the watchdog can run + * on, not the mask of cpus it is actually running on. This allows the + * user to specify a mask that will include cpus that have not yet + * been brought online, if desired. + */ +int proc_watchdog_cpumask(struct ctl_table *table, int write, + void __user *buffer, size_t *lenp, loff_t *ppos) +{ + int err; + + mutex_lock(&watchdog_proc_mutex); + err = proc_do_large_bitmap(table, write, buffer, lenp, ppos); + if (!err && write) { + /* Remove impossible cpus to keep sysctl output cleaner. */ + cpumask_and(watchdog_cpumask, watchdog_cpumask, + cpu_possible_mask); + + if (watchdog_enabled && watchdog_thresh) + smpboot_update_cpumask_percpu_thread(&watchdog_threads); + } + mutex_unlock(&watchdog_proc_mutex); + return err; +} + #endif /* CONFIG_SYSCTL */ void __init lockup_detector_init(void) { set_sample_period(); + alloc_cpumask_var(&watchdog_cpumask, GFP_KERNEL); + watchdog_threads.cpumask = watchdog_cpumask; + +#ifdef CONFIG_NO_HZ_FULL + if (!cpumask_empty(tick_nohz_full_mask)) + pr_info("Disabling watchdog on nohz_full cores by default\n"); + cpumask_andnot(watchdog_cpumask, cpu_possible_mask, + tick_nohz_full_mask); +#else + cpumask_copy(watchdog_cpumask, cpu_possible_mask); +#endif + + /* The sysctl API requires a variable holding a pointer to the mask. */ + watchdog_cpumask_bits = cpumask_bits(watchdog_cpumask); + if (watchdog_enabled) watchdog_enable_all_cpus(); } -- 2.1.2 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
