Messages in this thread |  | | Date | Wed, 5 Nov 2025 12:31:00 -0800 | | From | "Paul E. McKenney" <> | | Subject | [PATCH v2 0/16] SRCU updates for v6.19 |
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Hello!
This series creates an srcu_expedite_current() function that allows after-the-fact expediting of SRCU grace periods, adds a DEFINE_SRCU_FAST() that further speeds things up by removing a conditional branch from srcu_read_lock_fast*(), updates documentation, uses SRCU-fast to guard event traces in PREEMPT_RT kernel (thus making such kernels safe for event tracing), adds srcu_read_{,un}lock_fast_updown() functions that are compatible with srcu_down_read() and srcu_up_read(), but do not permit use in NMI handlers (to permit further optimization of SRCU-fast readers by relieving them of the need to deal with irq/softirq/NMI handlers with unbalanced lock/unlock calls), and optimizes SRCU-fast-updown for large ARM servers that use LSE. It is expected that this optimization will be obsoleted by some arm64 architecture-specific work:
https://lore.kernel.org/all/aQU7l-qMKJTx4znJ@arm.com/
The patches are as follows:
1. Permit Tiny SRCU srcu_read_unlock() with interrupts disabled.
2. Create an srcu_expedite_current() function.
3. Test srcu_expedite_current().
4. Create a DEFINE_SRCU_FAST().
5. Make grace-period determination use ssp->srcu_reader_flavor.
6. Exercise DEFINE_STATIC_SRCU_FAST() and init_srcu_struct_fast().
7. Require special srcu_struct define/init for SRCU-fast readers.
8. Make SRCU-fast readers enforce use of SRCU-fast definition/init.
9. Update for SRCU-fast definitions and initialization.
10. Guard __DECLARE_TRACE() use of __DO_TRACE_CALL() with SRCU-fast.
11. Mark diagnostic functions as notrace.
12. Add SRCU_READ_FLAVOR_FAST_UPDOWN CPP macro.
13. Permit negative kvm.sh --kconfig numberic arguments.
14. Create an SRCU-fast-updown API.
15. Optimize SRCU-fast-updown for arm64.
16. Make srcu{,d}_torture_init() announce the SRCU type.
Changes since v1:
o Merge addition and testing of SRCU-fast-updown for bisectability.
https://lore.kernel.org/all/082fb8ba-91b8-448e-a472-195eb7b282fd@paulmck-laptop/
Many of these patches were previously associated with another series that re-implemented RCU tasks trace in terms of SRCU-fast. This work is being deferred pending resolution of the ARM LSE situation on the one hand or full debugging of the all-too-clever workaround optimization on the other. ;-)
https://lore.kernel.org/all/7fa58961-2dce-4e08-8174-1d1cc592210f@paulmck-laptop/
Thanx, Paul
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b/Documentation/RCU/Design/Requirements/Requirements.rst | 33 +-- b/Documentation/RCU/checklist.rst | 12 - b/Documentation/RCU/whatisRCU.rst | 3 b/include/linux/notifier.h | 2 b/include/linux/srcu.h | 16 + b/include/linux/srcutiny.h | 1 b/include/linux/srcutree.h | 8 b/include/linux/tracepoint.h | 45 ++-- b/include/trace/perf.h | 4 b/include/trace/trace_events.h | 4 b/kernel/rcu/rcutorture.c | 12 + b/kernel/rcu/srcutiny.c | 13 - b/kernel/rcu/srcutree.c | 58 +++++ b/kernel/rcu/tree.c | 2 b/kernel/rcu/update.c | 8 b/kernel/tracepoint.c | 21 +- b/tools/testing/selftests/rcutorture/bin/kvm.sh | 2 include/linux/srcu.h | 133 ++++++++++--- include/linux/srcutiny.h | 30 ++ include/linux/srcutree.h | 152 +++++++++++---- kernel/rcu/rcutorture.c | 84 ++++++-- kernel/rcu/srcutree.c | 78 +++++++ 22 files changed, 575 insertions(+), 146 deletions(-)
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