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rcu/nocb: Check for deferred nocb wakeups before nohz_full early exit
In theory, a timer is used to defer wakeups of no-CBs grace-period kthreads when the wakeup cannot be done safely directly from the call_rcu(). In practice, the one-jiffy delay is not always consistent with timely callback invocation under heavy call_rcu() loads. Therefore, there are a number of checks for a pending deferred wakeup, including from the scheduling-clock interrupt. Unfortunately, this check follows the rcu_nohz_full_cpu() early exit, which renders it useless on such CPUs. This commit therefore moves the check for the pending deferred no-CB wakeup to precede the rcu_nohz_full_cpu() early exit. Signed-off-by: Paul E. McKenney <paulmck@linux.ibm.com>
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1 changed files with 4 additions and 4 deletions
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@ -2739,6 +2739,10 @@ static int rcu_pending(void)
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/* Check for CPU stalls, if enabled. */
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check_cpu_stall(rdp);
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/* Does this CPU need a deferred NOCB wakeup? */
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if (rcu_nocb_need_deferred_wakeup(rdp))
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return 1;
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/* Is this CPU a NO_HZ_FULL CPU that should ignore RCU? */
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if (rcu_nohz_full_cpu())
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return 0;
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@ -2763,10 +2767,6 @@ static int rcu_pending(void)
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unlikely(READ_ONCE(rdp->gpwrap))) /* outside lock */
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return 1;
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/* Does this CPU need a deferred NOCB wakeup? */
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if (rcu_nocb_need_deferred_wakeup(rdp))
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return 1;
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/* nothing to do */
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return 0;
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}
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