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| author | Steven Rostedt (VMware) <rostedt@goodmis.org> | 2018-05-25 01:49:46 +0300 |
|---|---|---|
| committer | Paul E. McKenney <paulmck@linux.vnet.ibm.com> | 2018-07-13 01:39:21 +0300 |
| commit | c03be752d39dc64dcfda0ac8ce87fb10b1ee5621 (patch) | |
| tree | 7fa3b8a9bb7dd09558e6d549de49fcecee81d262 /kernel/rcu/update.c | |
| parent | 0d805a70a652a6eef8d0283e5183879e7acb85ad (diff) | |
| download | linux-c03be752d39dc64dcfda0ac8ce87fb10b1ee5621.tar.xz | |
rcu: Speed up calling of RCU tasks callbacks
Joel Fernandes found that the synchronize_rcu_tasks() was taking a
significant amount of time. He demonstrated it with the following test:
# cd /sys/kernel/tracing
# while [ 1 ]; do x=1; done &
# echo '__schedule_bug:traceon' > set_ftrace_filter
# time echo '!__schedule_bug:traceon' > set_ftrace_filter;
real 0m1.064s
user 0m0.000s
sys 0m0.004s
Where it takes a little over a second to perform the synchronize,
because there's a loop that waits 1 second at a time for tasks to get
through their quiescent points when there's a task that must be waited
for.
After discussion we came up with a simple way to wait for holdouts but
increase the time for each iteration of the loop but no more than a
full second.
With the new patch we have:
# time echo '!__schedule_bug:traceon' > set_ftrace_filter;
real 0m0.131s
user 0m0.000s
sys 0m0.004s
Which drops it down to 13% of what the original wait time was.
Link: http://lkml.kernel.org/r/20180523063815.198302-2-joel@joelfernandes.org
Reported-by: Joel Fernandes (Google) <joel@joelfernandes.org>
Suggested-by: Joel Fernandes (Google) <joel@joelfernandes.org>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Diffstat (limited to 'kernel/rcu/update.c')
| -rw-r--r-- | kernel/rcu/update.c | 17 |
1 files changed, 15 insertions, 2 deletions
diff --git a/kernel/rcu/update.c b/kernel/rcu/update.c index 5783bdf86e5a..4c7c49c106ee 100644 --- a/kernel/rcu/update.c +++ b/kernel/rcu/update.c @@ -668,6 +668,7 @@ static int __noreturn rcu_tasks_kthread(void *arg) struct rcu_head *list; struct rcu_head *next; LIST_HEAD(rcu_tasks_holdouts); + int fract; /* Run on housekeeping CPUs by default. Sysadm can move if desired. */ housekeeping_affine(current, HK_FLAG_RCU); @@ -749,13 +750,25 @@ static int __noreturn rcu_tasks_kthread(void *arg) * holdouts. When the list is empty, we are done. */ lastreport = jiffies; - while (!list_empty(&rcu_tasks_holdouts)) { + + /* Start off with HZ/10 wait and slowly back off to 1 HZ wait*/ + fract = 10; + + for (;;) { bool firstreport; bool needreport; int rtst; struct task_struct *t1; - schedule_timeout_interruptible(HZ); + if (list_empty(&rcu_tasks_holdouts)) + break; + + /* Slowly back off waiting for holdouts */ + schedule_timeout_interruptible(HZ/fract); + + if (fract > 1) + fract--; + rtst = READ_ONCE(rcu_task_stall_timeout); needreport = rtst > 0 && time_after(jiffies, lastreport + rtst); |