On Tue, Sep 23, 2025 at 4:21 PM Paul E. McKenney <paul...@kernel.org> wrote:
>
> Hello!
>
> This series re-implements RCU Tasks Trace in terms of SRCU-fast,
> reducing the size of the Linux-kernel RCU implementation by several
> hundred lines of code. It also removes a conditional branch from the
> srcu_read_lock_fast() implementation in order to make SRCU-fast a
> bit more fastpath-friendly. The patches are as follows:
>
> 1. Re-implement RCU Tasks Trace in terms of SRCU-fast.
>
> 2. Remove unused ->trc_ipi_to_cpu and ->trc_blkd_cpu from
> task_struct.
>
> 3. Remove ->trc_blkd_node from task_struct.
>
> 4. Remove ->trc_holdout_list from task_struct.
>
> 5. Remove rcu_tasks_trace_qs() and the functions that it calls.
>
> 6. context_tracking: Remove
> rcu_task_trace_heavyweight_{enter,exit}().
>
> 7. Remove ->trc_reader_special from task_struct.
>
> 8. Remove now-empty RCU Tasks Trace functions and calls to them.
>
> 9. Remove unused rcu_tasks_trace_lazy_ms and trc_stall_chk_rdr
> struct.
>
> 10. Remove now-empty show_rcu_tasks_trace_gp_kthread() function.
>
> 11. Remove now-empty rcu_tasks_trace_get_gp_data() function.
>
> 12. Remove now-empty rcu_tasks_trace_torture_stats_print() function.
>
> 13. Remove now-empty get_rcu_tasks_trace_gp_kthread() function.
>
> 14. Move rcu_tasks_trace_srcu_struct out of #ifdef
> CONFIG_TASKS_RCU_GENERIC.
>
> 15. Add noinstr-fast rcu_read_{,un}lock_tasks_trace() APIs.
>
> 16. Remove now-unused rcu_task_ipi_delay and TASKS_TRACE_RCU_READ_MB.
>
> 17. Create a DEFINE_SRCU_FAST().
>
> 18. Use smp_mb() only when necessary in RCU Tasks Trace readers.
>
> 19. Update Requirements.rst for RCU Tasks Trace.
>
> 20. Deprecate rcu_read_{,un}lock_trace().
>
> 21. Mark diagnostic functions as notrace.
>
> 22. Guard __DECLARE_TRACE() use of __DO_TRACE_CALL() with SRCU-fast.
>
> 23. Create an srcu_expedite_current() function.
>
> 24. Test srcu_expedite_current().
>
> 25. Create an rcu_tasks_trace_expedite_current() function.
>
> 26. Test rcu_tasks_trace_expedite_current().
>
> 27. Make DEFINE_SRCU_FAST() available to modules.
>
> 28. Make SRCU-fast available to heap srcu_struct structures.
>
> 29. Make grace-period determination use ssp->srcu_reader_flavor.
>
> 30. Exercise DEFINE_STATIC_SRCU_FAST() and init_srcu_struct_fast().
>
> 31. Exercise DEFINE_STATIC_SRCU_FAST() and init_srcu_struct_fast().
>
> 32. Require special srcu_struct define/init for SRCU-fast readers.
>
> 33. Make SRCU-fast readers enforce use of SRCU-fast definition/init.
>
> 34. Update for SRCU-fast definitions and initialization.
Maybe it's just me, but the patch set is too fine grained.
These 34 patches could be squashed into a handful for better
review. All these steps: add smp_mb(), make it conditional,
make it more conditional, remove one field,
remove another field is a distraction from actual logic at the end.
