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| author | Paul E. McKenney <paul.mckenney@linaro.org> | 2011-11-22 17:46:19 -0800 |
|---|---|---|
| committer | Paul E. McKenney <paulmck@linux.vnet.ibm.com> | 2011-12-11 10:32:01 -0800 |
| commit | 84ad00cb61f1cb21f0b63bc6f7dc254399eb3830 (patch) | |
| tree | 7f275af0caaead54a5e8847afa308f5e2b33997a /kernel/rcutree_plugin.h | |
| parent | 3084f2f80cc8a1fd66233722d88beac0fe85e26f (diff) | |
| download | linux-84ad00cb61f1cb21f0b63bc6f7dc254399eb3830.tar.bz2 | |
rcu: Avoid needlessly IPIing CPUs at GP end
If a CPU enters dyntick-idle mode with callbacks pending, it will need
an IPI at the end of the grace period. However, if it exits dyntick-idle
mode before the grace period ends, it will be needlessly IPIed at the
end of the grace period.
Therefore, this commit clears the per-CPU rcu_awake_at_gp_end flag
when a CPU determines that it does not need it. This in turn requires
disabling interrupts across much of rcu_prepare_for_idle() in order to
avoid having nested interrupts clearing this state out from under us.
Signed-off-by: Paul E. McKenney <paul.mckenney@linaro.org>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Diffstat (limited to 'kernel/rcutree_plugin.h')
| -rw-r--r-- | kernel/rcutree_plugin.h | 16 |
1 files changed, 14 insertions, 2 deletions
diff --git a/kernel/rcutree_plugin.h b/kernel/rcutree_plugin.h index 45790bfb6e8c..c4daf1e19e01 100644 --- a/kernel/rcutree_plugin.h +++ b/kernel/rcutree_plugin.h @@ -2027,6 +2027,9 @@ int rcu_needs_cpu(int cpu) static void rcu_prepare_for_idle(int cpu) { int c = 0; + unsigned long flags; + + local_irq_save(flags); /* * If there are no callbacks on this CPU or if RCU has no further @@ -2036,14 +2039,17 @@ static void rcu_prepare_for_idle(int cpu) if (!rcu_cpu_has_callbacks(cpu)) { per_cpu(rcu_dyntick_holdoff, cpu) = jiffies - 1; per_cpu(rcu_dyntick_drain, cpu) = 0; + per_cpu(rcu_awake_at_gp_end, cpu) = 0; + local_irq_restore(flags); trace_rcu_prep_idle("No callbacks"); return; } if (!rcu_pending(cpu)) { - trace_rcu_prep_idle("Dyntick with callbacks"); per_cpu(rcu_dyntick_holdoff, cpu) = jiffies - 1; per_cpu(rcu_dyntick_drain, cpu) = 0; per_cpu(rcu_awake_at_gp_end, cpu) = 1; + local_irq_restore(flags); + trace_rcu_prep_idle("Dyntick with callbacks"); return; /* Nothing to do immediately. */ } @@ -2052,6 +2058,7 @@ static void rcu_prepare_for_idle(int cpu) * refrained from disabling the scheduling-clock tick. */ if (per_cpu(rcu_dyntick_holdoff, cpu) == jiffies) { + local_irq_restore(flags); trace_rcu_prep_idle("In holdoff"); return; } @@ -2060,9 +2067,11 @@ static void rcu_prepare_for_idle(int cpu) if (per_cpu(rcu_dyntick_drain, cpu) <= 0) { /* First time through, initialize the counter. */ per_cpu(rcu_dyntick_drain, cpu) = RCU_NEEDS_CPU_FLUSHES; + per_cpu(rcu_awake_at_gp_end, cpu) = 0; } else if (--per_cpu(rcu_dyntick_drain, cpu) <= 0) { /* We have hit the limit, so time to give up. */ per_cpu(rcu_dyntick_holdoff, cpu) = jiffies; + local_irq_restore(flags); trace_rcu_prep_idle("Begin holdoff"); invoke_rcu_core(); /* Force the CPU out of dyntick-idle. */ return; @@ -2095,10 +2104,13 @@ static void rcu_prepare_for_idle(int cpu) * So try forcing the callbacks through the grace period. */ if (c) { + local_irq_restore(flags); trace_rcu_prep_idle("More callbacks"); invoke_rcu_core(); - } else + } else { + local_irq_restore(flags); trace_rcu_prep_idle("Callbacks drained"); + } } /* |