diff options
Diffstat (limited to 'Documentation/timers/NO_HZ.txt')
-rw-r--r-- | Documentation/timers/NO_HZ.txt | 21 |
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 | |||
278 | single runnable SCHED_FIFO task and multiple runnable SCHED_OTHER | 278 | single runnable SCHED_FIFO task and multiple runnable SCHED_OTHER |
279 | tasks, even though these interrupts are unnecessary. | 279 | tasks, even though these interrupts are unnecessary. |
280 | 280 | ||
281 | And even when there are multiple runnable tasks on a given CPU, | ||
282 | there is little point in interrupting that CPU until the current | ||
283 | running task's timeslice expires, which is almost always way | ||
284 | longer than the time of the next scheduling-clock interrupt. | ||
285 | |||
281 | Better handling of these sorts of situations is future work. | 286 | Better handling of these sorts of situations is future work. |
282 | 287 | ||
283 | o A reboot is required to reconfigure both adaptive idle and RCU | 288 | 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 | |||
308 | scheduling-clock interrupt going in order to support accurate | 313 | scheduling-clock interrupt going in order to support accurate |
309 | timekeeping. | 314 | timekeeping. |
310 | 315 | ||
311 | o If there are adaptive-ticks CPUs, there will be at least one | 316 | o If there might potentially be some adaptive-ticks CPUs, there |
312 | CPU keeping the scheduling-clock interrupt going, even if all | 317 | will be at least one CPU keeping the scheduling-clock interrupt |
313 | CPUs are otherwise idle. | 318 | going, even if all CPUs are otherwise idle. |
319 | |||
320 | Better handling of this situation is ongoing work. | ||
321 | |||
322 | o Some process-handling operations still require the occasional | ||
323 | scheduling-clock tick. These operations include calculating CPU | ||
324 | load, maintaining sched average, computing CFS entity vruntime, | ||
325 | computing avenrun, and carrying out load balancing. They are | ||
326 | currently accommodated by scheduling-clock tick every second | ||
327 | or so. On-going work will eliminate the need even for these | ||
328 | infrequent scheduling-clock ticks. | ||