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rcu: Update Requirements.rst for RCU Tasks Trace

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This commit updates the documentation to declare that RCU Tasks Trace
is implemented as a thin wrapper around SRCU-fast.

Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Cc: Andrii Nakryiko <andrii@kernel.org>
Cc: Alexei Starovoitov <ast@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: bpf@vger.kernel.org
Reviewed-by: Joel Fernandes <joelagnelf@nvidia.com>
Signed-off-by: Boqun Feng <boqun.feng@gmail.com>
This commit is contained in:
Paul E. McKenney
2025-12-29 11:11:01 -08:00
committed by Boqun Feng
parent 1a72f4bb6f
commit c0872be261
1 changed files with 6 additions and 6 deletions
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12
Documentation/RCU/Design/Requirements/Requirements.rst
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@@ -2780,12 +2780,12 @@ Tasks Trace RCU
~~~~~~~~~~~~~~~
Some forms of tracing need to sleep in readers, but cannot tolerate
SRCU's read-side overhead, which includes a full memory barrier in both
srcu_read_lock() and srcu_read_unlock(). This need is handled by a
Tasks Trace RCU that uses scheduler locking and IPIs to synchronize with
readers. Real-time systems that cannot tolerate IPIs may build their
kernels with ``CONFIG_TASKS_TRACE_RCU_READ_MB=y``, which avoids the IPIs at
the expense of adding full memory barriers to the read-side primitives.
SRCU's read-side overhead, which includes a full memory barrier in
both srcu_read_lock() and srcu_read_unlock(). This need is handled by
a Tasks Trace RCU API implemented as thin wrappers around SRCU-fast,
which avoids the read-side memory barriers, at least for architectures
that apply noinstr to kernel entry/exit code (or that build with
``CONFIG_TASKS_TRACE_RCU_NO_MB=y``.
The tasks-trace-RCU API is also reasonably compact,
consisting of rcu_read_lock_trace(), rcu_read_unlock_trace(),