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-rw-r--r--Documentation/kernel-parameters.txt4
-rw-r--r--kernel/time/tick-sched.c54
2 files changed, 17 insertions, 41 deletions
diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt
index 82365dde00a8..887b29708447 100644
--- a/Documentation/kernel-parameters.txt
+++ b/Documentation/kernel-parameters.txt
@@ -1916,8 +1916,8 @@ bytes respectively. Such letter suffixes can also be entirely omitted.
nohz_full= [KNL,BOOT]
In kernels built with CONFIG_NO_HZ_FULL=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.
+ whenever possible. The boot CPU will be forced outside
+ the range to maintain the timekeeping.
noiotrap [SH] Disables trapped I/O port accesses.
diff --git a/kernel/time/tick-sched.c b/kernel/time/tick-sched.c
index 369b5769fc97..2bac5ea2c9af 100644
--- a/kernel/time/tick-sched.c
+++ b/kernel/time/tick-sched.c
@@ -158,11 +158,21 @@ int tick_nohz_full_cpu(int cpu)
/* Parse the boot-time nohz CPU list from the kernel parameters. */
static int __init tick_nohz_full_setup(char *str)
{
+ int cpu;
+
alloc_bootmem_cpumask_var(&nohz_full_mask);
- if (cpulist_parse(str, nohz_full_mask) < 0)
+ if (cpulist_parse(str, nohz_full_mask) < 0) {
pr_warning("NOHZ: Incorrect nohz_full cpumask\n");
- else
- have_nohz_full_mask = true;
+ return 1;
+ }
+
+ cpu = smp_processor_id();
+ if (cpumask_test_cpu(cpu, nohz_full_mask)) {
+ pr_warning("NO_HZ: Clearing %d from nohz_full range for timekeeping\n", cpu);
+ cpumask_clear_cpu(cpu, nohz_full_mask);
+ }
+ have_nohz_full_mask = true;
+
return 1;
}
__setup("nohz_full=", tick_nohz_full_setup);
@@ -195,42 +205,8 @@ static char __initdata nohz_full_buf[NR_CPUS + 1];
static int __init init_tick_nohz_full(void)
{
- cpumask_var_t online_nohz;
- int cpu;
-
- if (!have_nohz_full_mask)
- return 0;
-
- cpu_notifier(tick_nohz_cpu_down_callback, 0);
-
- if (!zalloc_cpumask_var(&online_nohz, GFP_KERNEL)) {
- pr_warning("NO_HZ: Not enough memory to check full 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_full_mask);
- if (cpumask_equal(online_nohz, cpu_online_mask)) {
- pr_warning("NO_HZ: Must keep at least one online CPU "
- "out of nohz_full range\n");
- /*
- * We know the current CPU doesn't have its tick stopped.
- * Let's use it for the timekeeping duty.
- */
- preempt_disable();
- cpu = smp_processor_id();
- pr_warning("NO_HZ: Clearing %d from nohz_full range\n", cpu);
- cpumask_clear_cpu(cpu, nohz_full_mask);
- preempt_enable();
- }
- put_online_cpus();
- free_cpumask_var(online_nohz);
+ if (have_nohz_full_mask)
+ cpu_notifier(tick_nohz_cpu_down_callback, 0);
cpulist_scnprintf(nohz_full_buf, sizeof(nohz_full_buf), nohz_full_mask);
pr_info("NO_HZ: Full dynticks CPUs: %s.\n", nohz_full_buf);