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rcu: Avoid self-IPI in sync_rcu_exp_select_node_cpus()

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Although sync_rcu_exp_select_node_cpus() treats the current CPU as being
in a quiescent state, it might well migrate to some other CPU before
reaching the smp_call_function_single(), which could then result in an
unnecessary simulated self-IPI.  This commit therefore instead simply
refuses to invoke smp_call_function_single() on the current CPU, which
causes the later rcu_report_exp_cpu_mult() to report this CPU's quiescent
state with less overhead.

This also reduces the rcu_exp_handler() function's state space by removing
the direct call that this smp_call_function_single() uses to emulate the
requested self-IPI.

Signed-off-by: Paul E. McKenney <paulmck@linux.ibm.com>
[ paulmck: Use get_cpu() instead of preempt_disable() per Joel Fernandes. ]
This commit is contained in:
Paul E. McKenney 2019-03-27 09:09:47 -07:00
parent 43e903ad3e
commit b9ad4d6ed1
1 changed files with 5 additions and 0 deletions
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5
kernel/rcu/tree_exp.h
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@ -384,7 +384,12 @@ retry_ipi:
mask_ofl_test |= mask; mask_ofl_test |= mask;
continue; continue;
} }
if (get_cpu() == cpu) {
put_cpu();
continue;
}
ret = smp_call_function_single(cpu, rcu_exp_handler, NULL, 0); ret = smp_call_function_single(cpu, rcu_exp_handler, NULL, 0);
put_cpu();
if (!ret) { if (!ret) {
mask_ofl_ipi &= ~mask; mask_ofl_ipi &= ~mask;
continue; continue;