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authorPaul E. McKenney <paulmck@linux.vnet.ibm.com>2010-04-14 17:39:26 -0700
committerPaul E. McKenney <paulmck@linux.vnet.ibm.com>2010-05-10 11:08:35 -0700
commitd21670acab9fcb4bc74a40b68a6941059234c55c (patch)
tree6a4c054bc4dbadf0524b4e221889a8da558dbdaf /kernel/rcutree_trace.c
parent4a90a0681cf6cd21cd444184302aa045156486b3 (diff)
downloadlwn-d21670acab9fcb4bc74a40b68a6941059234c55c.tar.gz
lwn-d21670acab9fcb4bc74a40b68a6941059234c55c.zip
rcu: reduce the number of spurious RCU_SOFTIRQ invocations
Lai Jiangshan noted that up to 10% of the RCU_SOFTIRQ are spurious, and traced this down to the fact that the current grace-period machinery will uselessly raise RCU_SOFTIRQ when a given CPU needs to go through a quiescent state, but has not yet done so. In this situation, there might well be nothing that RCU_SOFTIRQ can do, and the overhead can be worth worrying about in the ksoftirqd case. This patch therefore avoids raising RCU_SOFTIRQ in this situation. Changes since v1 (http://lkml.org/lkml/2010/3/30/122 from Lai Jiangshan): o Omit the rcu_qs_pending() prechecks, as they aren't that much less expensive than the quiescent-state checks. o Merge with the set_need_resched() patch that reduces IPIs. o Add the new n_rp_report_qs field to the rcu_pending tracing output. o Update the tracing documentation accordingly. Signed-off-by: Lai Jiangshan <laijs@cn.fujitsu.com> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Diffstat (limited to 'kernel/rcutree_trace.c')
-rw-r--r--kernel/rcutree_trace.c4
1 files changed, 3 insertions, 1 deletions
diff --git a/kernel/rcutree_trace.c b/kernel/rcutree_trace.c
index d45db2e35d27..36c95b45738e 100644
--- a/kernel/rcutree_trace.c
+++ b/kernel/rcutree_trace.c
@@ -241,11 +241,13 @@ static const struct file_operations rcugp_fops = {
static void print_one_rcu_pending(struct seq_file *m, struct rcu_data *rdp)
{
seq_printf(m, "%3d%cnp=%ld "
- "qsp=%ld cbr=%ld cng=%ld gpc=%ld gps=%ld nf=%ld nn=%ld\n",
+ "qsp=%ld rpq=%ld cbr=%ld cng=%ld "
+ "gpc=%ld gps=%ld nf=%ld nn=%ld\n",
rdp->cpu,
cpu_is_offline(rdp->cpu) ? '!' : ' ',
rdp->n_rcu_pending,
rdp->n_rp_qs_pending,
+ rdp->n_rp_report_qs,
rdp->n_rp_cb_ready,
rdp->n_rp_cpu_needs_gp,
rdp->n_rp_gp_completed,