[PATCH 0/3] v2 Make hierarchical RCU less IPI-happy and add more tracing

[Paul E. McKenney]

This three-patch set fixes a hierarchical-RCU performance bug located
by Anton Blanchard.  This bug affects certain high-end floating-point
computation-heavy workloads with closely spaced barrier-synchronized
iterations, where an interruption of any one CPU's processing during a
given iteration slows the system as a whole.  This bug manifests itself
as excessive resched IPIs, and is strictly a performance regression.
It does not affect correctness.

The first patch provides the fix for the problem, the second patch
adds the tracing, and the third patch adds the documentation for the
tracing.

Located-by: Anton Blanchard <anton@xxxxxxxxxxx>
Tested-by: Anton Blanchard <anton@xxxxxxxxxxx>
Signed-off-by: Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx>
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