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-rw-r--r--Documentation/timers/NO_HZ.txt21
1 files changed, 18 insertions, 3 deletions
diff --git a/Documentation/timers/NO_HZ.txt b/Documentation/timers/NO_HZ.txt
index d5323e075550..88697584242b 100644
--- a/Documentation/timers/NO_HZ.txt
+++ b/Documentation/timers/NO_HZ.txt
@@ -278,6 +278,11 @@ o Adaptive-ticks does not do anything unless there is only one
single runnable SCHED_FIFO task and multiple runnable SCHED_OTHER
tasks, even though these interrupts are unnecessary.
+ And even when there are multiple runnable tasks on a given CPU,
+ there is little point in interrupting that CPU until the current
+ running task's timeslice expires, which is almost always way
+ longer than the time of the next scheduling-clock interrupt.
+
Better handling of these sorts of situations is future work.
o A reboot is required to reconfigure both adaptive idle and RCU
@@ -308,6 +313,16 @@ o Unless all CPUs are idle, at least one CPU must keep the
scheduling-clock interrupt going in order to support accurate
timekeeping.
-o If there are adaptive-ticks CPUs, there will be at least one
- CPU keeping the scheduling-clock interrupt going, even if all
- CPUs are otherwise idle.
+o If there might potentially be some adaptive-ticks CPUs, there
+ will be at least one CPU keeping the scheduling-clock interrupt
+ going, even if all CPUs are otherwise idle.
+
+ Better handling of this situation is ongoing work.
+
+o Some process-handling operations still require the occasional
+ scheduling-clock tick. These operations include calculating CPU
+ load, maintaining sched average, computing CFS entity vruntime,
+ computing avenrun, and carrying out load balancing. They are
+ currently accommodated by scheduling-clock tick every second
+ or so. On-going work will eliminate the need even for these
+ infrequent scheduling-clock ticks.