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    SubjectRe: [PATCH tip/core/rcu 0/19] RCU flavor-consolidation changes for v4.20/v5.0
    On Wed, Aug 29, 2018 at 03:20:21PM -0700, Paul E. McKenney wrote:
    > Hello!
    >
    > This series contains the RCU flavor consolidation, along with some initial
    > cleanup work enabled by that consolidation (and some that became apparent
    > while cleaning up):
    >
    > 1. Refactor rcu_{nmi,irq}_{enter,exit}(), saving a branch on the
    > idle entry/exit hotpaths, courtesy of Byungchul Park,
    >
    > 2. Defer reporting RCU-preempt quiescent states when disabled.
    > This is the key commit that consolidates the RCU-bh and RCU-sched
    > flavors into RCU, however, the RCU-bh and RCU-sched flavors
    > still exist independently as well at this point.
    >
    > 3. Test extended "rcu" read-side critical sections. This commit
    > causes rcutorture to test RCU's new-found ability to act as
    > the combination of RCU, RCU-bh, and RCU-sched.
    >
    > 4. Allow processing deferred QSes for exiting RCU-preempt readers.
    > This is a optimization.
    >
    > 5. Remove now-unused ->b.exp_need_qs field from the rcu_special union.
    >
    > 6. Add warning to detect half-interrupts. Test the claim that
    > the Linux kernel no longer does half-interrupts.
    >
    > 7. Apply RCU-bh QSes to RCU-sched and RCU-preempt when safe, that is,
    > make the consolidated RCU inherit RCU-bh's denial-of-service
    > avoidance mechanism.
    >
    > 8. Report expedited grace periods at context-switch time. This is
    > an optimization enabled by the RCU flavor consolidation.
    >
    > 9. Define RCU-bh update API in terms of RCU. This commit gets rid
    > of the RCU-bh update mechanism.
    >
    > 10. Update comments and help text to account for the removal of
    > the RCU-bh update mechanism.
    >
    > 11. Drop "wake" parameter from rcu_report_exp_rdp().
    >
    > 12. Fix typo in rcu_get_gp_kthreads_prio() header comment.
    >
    > 13. Define RCU-sched API in terms of RCU for Tree RCU PREEMPT builds.
    > Although this commit gets rid of the RCU-sched update mechanism
    > from PREEMPT builds, it of course remains as the sole RCU flavor
    > for !PREEMPT && !SMP builds.
    >
    > 14. Express Tiny RCU updates in terms of RCU rather than RCU-sched.
    > This will enable additional cleanups and code savings.
    >
    > 15. Remove RCU_STATE_INITIALIZER() in favor of just using an open-coded
    > initializer for the sole remaining rcu_state structure.
    >
    > 16. Eliminate rcu_state structure's ->call field, as it is now always
    > just call_rcu().
    >
    > 17. Remove rcu_state structure's ->rda field, as there is now only one
    > set of per-CPU rcu_data structures.

    And last, but perhaps not least:

    18. Remove rcu_state_p pointer to default rcu_state structure, now
    that there is only one rcu_state structure.

    19. Remove rcu_data_p pointer to default rcu_data structure, now that
    there is only one set of per-CPU rcu_data structures.

    Thanx, Paul

    > ------------------------------------------------------------------------
    >
    > Documentation/RCU/Design/Requirements/Requirements.html | 50 -
    > include/linux/rcupdate.h | 48 -
    > include/linux/rcupdate_wait.h | 6
    > include/linux/rcutiny.h | 61 +
    > include/linux/rcutree.h | 31
    > include/linux/sched.h | 6
    > kernel/rcu/Kconfig | 10
    > kernel/rcu/rcutorture.c | 1
    > kernel/rcu/tiny.c | 163 +--
    > kernel/rcu/tree.c | 655 +++++-----------
    > kernel/rcu/tree.h | 44 -
    > kernel/rcu/tree_exp.h | 256 +++---
    > kernel/rcu/tree_plugin.h | 523 ++++++------
    > kernel/rcu/update.c | 2
    > kernel/softirq.c | 3
    > 15 files changed, 836 insertions(+), 1023 deletions(-)

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