diff options
| -rw-r--r-- | Documentation/kernel-parameters.txt | 6 | ||||
| -rw-r--r-- | include/linux/tick.h | 7 | ||||
| -rw-r--r-- | kernel/time/Kconfig | 19 | ||||
| -rw-r--r-- | kernel/time/tick-sched.c | 62 |
4 files changed, 94 insertions, 0 deletions
diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt index 4609e81dbc3..231698feadd 100644 --- a/Documentation/kernel-parameters.txt +++ b/Documentation/kernel-parameters.txt @@ -1913,6 +1913,12 @@ bytes respectively. Such letter suffixes can also be entirely omitted. Valid arguments: on, off Default: on + nohz_extended= [KNL,BOOT] + In kernels built with CONFIG_NO_HZ_EXTENDED=y, set + the specified list of CPUs whose tick will be stopped + whenever possible. You need to keep at least one online + CPU outside the range to maintain the timekeeping. + noiotrap [SH] Disables trapped I/O port accesses. noirqdebug [X86-32] Disables the code which attempts to detect and diff --git a/include/linux/tick.h b/include/linux/tick.h index 553272e6af5..44bfa8aa439 100644 --- a/include/linux/tick.h +++ b/include/linux/tick.h @@ -157,6 +157,13 @@ static inline u64 get_cpu_idle_time_us(int cpu, u64 *unused) { return -1; } static inline u64 get_cpu_iowait_time_us(int cpu, u64 *unused) { return -1; } # endif /* !NO_HZ */ +#ifdef CONFIG_NO_HZ_EXTENDED +extern int tick_nohz_extended_cpu(int cpu); +#else +static inline int tick_nohz_extended_cpu(int cpu) { return 0; } +#endif + + # ifdef CONFIG_CPU_IDLE_GOV_MENU extern void menu_hrtimer_cancel(void); # else diff --git a/kernel/time/Kconfig b/kernel/time/Kconfig index 24510d84efd..5a87c03e45a 100644 --- a/kernel/time/Kconfig +++ b/kernel/time/Kconfig @@ -79,6 +79,25 @@ config NO_HZ only trigger on an as-needed basis both when the system is busy and when the system is idle. +config NO_HZ_EXTENDED + bool "Full dynticks system" + depends on NO_HZ && RCU_USER_QS && VIRT_CPU_ACCOUNTING_GEN && RCU_NOCB_CPU && SMP + select CONTEXT_TRACKING_FORCE + help + Adaptively try to shutdown the tick whenever possible, even when + the CPU is running tasks. Typically this requires running a single + task on the CPU. Chances for running tickless are maximized when + the task mostly runs in userspace and has few kernel activity. + + You need to fill up the nohz_extended boot parameter with the + desired range of dynticks CPUs. + + This is implemented at the expense of some overhead in user <-> kernel + transitions: syscalls, exceptions and interrupts. Even when it's + dynamically off. + + Say N. + config HIGH_RES_TIMERS bool "High Resolution Timer Support" depends on !ARCH_USES_GETTIMEOFFSET && GENERIC_CLOCKEVENTS diff --git a/kernel/time/tick-sched.c b/kernel/time/tick-sched.c index a19a39952c1..79c275f08b7 100644 --- a/kernel/time/tick-sched.c +++ b/kernel/time/tick-sched.c @@ -142,6 +142,68 @@ static void tick_sched_handle(struct tick_sched *ts, struct pt_regs *regs) profile_tick(CPU_PROFILING); } +#ifdef CONFIG_NO_HZ_EXTENDED +static cpumask_var_t nohz_extended_mask; +bool have_nohz_extended_mask; + +int tick_nohz_extended_cpu(int cpu) +{ + if (!have_nohz_extended_mask) + return 0; + + return cpumask_test_cpu(cpu, nohz_extended_mask); +} + +/* Parse the boot-time nohz CPU list from the kernel parameters. */ +static int __init tick_nohz_extended_setup(char *str) +{ + alloc_bootmem_cpumask_var(&nohz_extended_mask); + if (cpulist_parse(str, nohz_extended_mask) < 0) + pr_warning("NOHZ: Incorrect nohz_extended cpumask\n"); + else + have_nohz_extended_mask = true; + return 1; +} +__setup("nohz_extended=", tick_nohz_extended_setup); + +static int __init init_tick_nohz_extended(void) +{ + cpumask_var_t online_nohz; + int cpu; + + if (!have_nohz_extended_mask) + return 0; + + if (!zalloc_cpumask_var(&online_nohz, GFP_KERNEL)) { + pr_warning("NO_HZ: Not enough memory to check extended nohz mask\n"); + return -ENOMEM; + } + + /* + * CPUs can probably not be concurrently offlined on initcall time. + * But we are paranoid, aren't we? + */ + get_online_cpus(); + + /* Ensure we keep a CPU outside the dynticks range for timekeeping */ + cpumask_and(online_nohz, cpu_online_mask, nohz_extended_mask); + if (cpumask_equal(online_nohz, cpu_online_mask)) { + cpu = cpumask_any(cpu_online_mask); + pr_warning("NO_HZ: Must keep at least one online CPU " + "out of nohz_extended range\n"); + pr_warning("NO_HZ: Clearing %d from nohz_extended range\n", cpu); + cpumask_clear_cpu(cpu, nohz_extended_mask); + } + put_online_cpus(); + free_cpumask_var(online_nohz); + + return 0; +} +core_initcall(init_tick_nohz_extended); +#else +#define have_nohz_extended_mask (0) +#endif + /* * NOHZ - aka dynamic tick functionality */ |