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authorPaul E. McKenney <paulmck@kernel.org>2021-04-14 13:00:10 -0700
committerPaul E. McKenney <paulmck@kernel.org>2021-05-10 16:05:07 -0700
commit063f5a4df99145ba0a5d4879d171a8175235f37b (patch)
tree71dbfa274cc1d7780ca193bd502591425372ab6d /kernel/rcu/rcutorture.c
parent0260b92e1c39412b1e345e202355c43169c16274 (diff)
rcutorture: Don't count CPU-stalled time against priority boosting
It will frequently be the case that rcu_torture_boost() will get a ->start_gp_poll() cookie that needs almost all of the current grace period plus an additional grace period to elapse before ->poll_gp_state() will return true. It is quite possible that the current grace period will have (say) two seconds of stall by a CPU failing to pass through a quiescent state, followed by 300 milliseconds of delay due to a preempted reader. The next grace period might suffer only one second of stall by a CPU, followed by another 300 milliseconds of delay due to a preempted reader. This is an example of RCU priority boosting doing its job, but the full elapsed time of 3.6 seconds exceeds the 3.5-second limit. In addition, there is no CPU stall in force at the 3.5-second mark, so this would nevertheless currently be counted as an RCU priority boosting failure. This commit therefore avoids this sort of false positive by resetting the gp_state_time timestamp any time that the current grace period is being blocked by a CPU. This results in extremely frequent calls to the ->check_boost_failed() function, so this commit provides a lockless fastpath that is selected by supplying a NULL CPU-number pointer. Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Diffstat (limited to 'kernel/rcu/rcutorture.c')
-rw-r--r--kernel/rcu/rcutorture.c13
1 files changed, 8 insertions, 5 deletions
diff --git a/kernel/rcu/rcutorture.c b/kernel/rcu/rcutorture.c
index 5ae4dcc6ba27..8b347b9659aa 100644
--- a/kernel/rcu/rcutorture.c
+++ b/kernel/rcu/rcutorture.c
@@ -918,17 +918,18 @@ static void rcu_torture_enable_rt_throttle(void)
old_rt_runtime = -1;
}
-static bool rcu_torture_boost_failed(unsigned long gp_state, unsigned long start, unsigned long end)
+static bool rcu_torture_boost_failed(unsigned long gp_state, unsigned long *start)
{
int cpu;
static int dbg_done;
+ unsigned long end = jiffies;
bool gp_done;
unsigned long j;
static unsigned long last_persist;
unsigned long lp;
unsigned long mininterval = test_boost_duration * HZ - HZ / 2;
- if (end - start > mininterval) {
+ if (end - *start > mininterval) {
// Recheck after checking time to avoid false positives.
smp_mb(); // Time check before grace-period check.
if (cur_ops->poll_gp_state(gp_state))
@@ -945,7 +946,7 @@ static bool rcu_torture_boost_failed(unsigned long gp_state, unsigned long start
n_rcu_torture_boost_failure++;
if (!xchg(&dbg_done, 1) && cur_ops->gp_kthread_dbg) {
pr_info("Boost inversion thread ->rt_priority %u gp_state %lu jiffies %lu\n",
- current->rt_priority, gp_state, end - start);
+ current->rt_priority, gp_state, end - *start);
cur_ops->gp_kthread_dbg();
// Recheck after print to flag grace period ending during splat.
gp_done = cur_ops->poll_gp_state(gp_state);
@@ -955,6 +956,8 @@ static bool rcu_torture_boost_failed(unsigned long gp_state, unsigned long start
}
return true; // failed
+ } else if (cur_ops->check_boost_failed && !cur_ops->check_boost_failed(gp_state, NULL)) {
+ *start = jiffies;
}
return false; // passed
@@ -995,7 +998,7 @@ static int rcu_torture_boost(void *arg)
while (time_before(jiffies, endtime)) {
// Has current GP gone too long?
if (gp_initiated && !failed && !cur_ops->poll_gp_state(gp_state))
- failed = rcu_torture_boost_failed(gp_state, gp_state_time, jiffies);
+ failed = rcu_torture_boost_failed(gp_state, &gp_state_time);
// If we don't have a grace period in flight, start one.
if (!gp_initiated || cur_ops->poll_gp_state(gp_state)) {
gp_state = cur_ops->start_gp_poll();
@@ -1016,7 +1019,7 @@ static int rcu_torture_boost(void *arg)
// In case the grace period extended beyond the end of the loop.
if (gp_initiated && !failed && !cur_ops->poll_gp_state(gp_state))
- rcu_torture_boost_failed(gp_state, gp_state_time, jiffies);
+ rcu_torture_boost_failed(gp_state, &gp_state_time);
/*
* Set the start time of the next test interval.