Commit-ID: 20377f32dcb77941d450728da18cce5b1a7faec5 Gitweb: http://git.kernel.org/tip/20377f32dcb77941d450728da18cce5b1a7faec5 Author: Frederic Weisbecker <fweisbec@xxxxxxxxx> AuthorDate: Fri, 10 Dec 2010 22:11:10 +0100 Committer: Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx> CommitDate: Fri, 17 Dec 2010 12:34:18 -0800 rcu: Stop chasing QS if another CPU did it for us When a CPU is idle and others CPUs handled its extended quiescent state to complete grace periods on its behalf, it will catch up with completed grace periods numbers when it wakes up. But at this point there might be no more grace period to complete, but still the woken CPU always keeps its stale qs_pending value and will then continue to chase quiescent states even if its not needed anymore. This results in clusters of spurious softirqs until a new real grace period is started. Because if we continue to chase quiescent states but we have completed every grace periods, rcu_report_qs_rdp() is puzzled and makes that state run into infinite loops. As suggested by Lai Jiangshan, just reset qs_pending if someone completed every grace periods on our behalf. Suggested-by: Lai Jiangshan <laijs@xxxxxxxxxxxxxx> Signed-off-by: Frederic Weisbecker <fweisbec@xxxxxxxxx> Cc: Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx> Cc: Ingo Molnar <mingo@xxxxxxx> Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx> Cc: Peter Zijlstra <a.p.zijlstra@xxxxxxxxx> Cc: Steven Rostedt <rostedt@xxxxxxxxxxx> Signed-off-by: Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx> --- kernel/rcutree.c | 8 ++++++++ 1 files changed, 8 insertions(+), 0 deletions(-) diff --git a/kernel/rcutree.c b/kernel/rcutree.c index 120820f..916f42b 100644 --- a/kernel/rcutree.c +++ b/kernel/rcutree.c @@ -678,6 +678,14 @@ __rcu_process_gp_end(struct rcu_state *rsp, struct rcu_node *rnp, struct rcu_dat /* Remember that we saw this grace-period completion. */ rdp->completed = rnp->completed; + + /* + * If another CPU handled our extended quiescent states and + * we have no more grace period to complete yet, then stop + * chasing quiescent states. + */ + if (rdp->completed == rnp->gpnum) + rdp->qs_pending = 0; } } -- To unsubscribe from this list: send the line "unsubscribe linux-tip-commits" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
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