tjh.dev
+2
-5
Documentation/timers/no_hz.rst
+2
-5
Documentation/timers/no_hz.rst
···
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online to handle timekeeping tasks in order to ensure that system
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calls like gettimeofday() returns accurate values on adaptive-tick CPUs.
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(This is not an issue for CONFIG_NO_HZ_IDLE=y because there are no running
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-
user processes to observe slight drifts in clock rate.) Therefore, the
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-
boot CPU is prohibited from entering adaptive-ticks mode. Specifying a
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-
"nohz_full=" mask that includes the boot CPU will result in a boot-time
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-
error message, and the boot CPU will be removed from the mask. Note that
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-
this means that your system must have at least two CPUs in order for
132
+
user processes to observe slight drifts in clock rate.) Note that this
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+
means that your system must have at least two CPUs in order for
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134
CONFIG_NO_HZ_FULL=y to do anything for you.
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135
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Finally, adaptive-ticks CPUs must have their RCU callbacks offloaded.
+10
-1
kernel/sched/isolation.c
+10
-1
kernel/sched/isolation.c
···
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46
if (cpu < nr_cpu_ids)
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47
return cpu;
48
48
49
-
return cpumask_any_and(housekeeping.cpumasks[type], cpu_online_mask);
49
+
cpu = cpumask_any_and(housekeeping.cpumasks[type], cpu_online_mask);
50
+
if (likely(cpu < nr_cpu_ids))
51
+
return cpu;
52
+
/*
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+
* Unless we have another problem this can only happen
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+
* at boot time before start_secondary() brings the 1st
55
+
* housekeeping CPU up.
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+
*/
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+
WARN_ON_ONCE(system_state == SYSTEM_RUNNING ||
58
+
type != HK_TYPE_TIMER);
50
59
}
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60
}
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61
return smp_processor_id();