Design/Expedited-Grace-Periods/Expedited-Grace-Periods.rst

2 A Tour Through TREE_RCU's Expedited Grace Periods
8 This document describes RCU's expedited grace periods.
9 Unlike RCU's normal grace periods, which accept long latencies to attain
10 high efficiency and minimal disturbance, expedited grace periods accept
20 The expedited RCU grace periods cannot be accused of being subtle,
38 RCU-preempt Expedited Grace Periods
112 RCU-sched Expedited Grace Periods
140 The expedited nature of expedited grace periods require a much tighter
142 grace periods. In addition, attempting to IPI offline CPUs will result
144 periods. Neither option is acceptable in production kernels.
146 The interaction between expedited grace periods and CPU hotplug
244 In summary, RCU expedited grace periods check for idle when building the
252 periods would have abysmal scalability and problematic high-load
262 the number of completed grace periods. During any given update request,
386 periods and carrying out their wakeups.
434 Expediting grace periods does nothing to speed things up when RCU
435 readers take too long, and therefore expedited grace periods check for
436 stalls just as normal grace periods do.
443 | expedited grace periods?                                              |
467 really do want to execute grace periods during this mid-boot “dead
468 zone”, expedited grace periods must do something else during this time.
477 Non-expedited non-SRCU synchronous grace periods must also operate
479 periods to take the expedited code path during mid-boot.
488 With this refinement, synchronous grace periods can now be used from
496 Expedited grace periods use a sequence-number approach to promote
505 tight synchronization between expedited grace periods and CPU-hotplug
517 This combination of mechanisms allows expedited grace periods to run
519 grace periods should be used instead because their longer duration