Messages in this thread | | | Date | Sun, 20 May 2018 20:02:25 -0700 | From | "Paul E. McKenney" <> | Subject | Re: [PATCH v2] rcu: Speed up calling of RCU tasks callbacks |
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On Sun, May 20, 2018 at 05:43:24PM -0700, Joel Fernandes wrote: > From: "Joel Fernandes (Google)" <joel@joelfernandes.org> > > RCU tasks callbacks can take atleast 1 second before the callbacks are > executed. This happens even if the hold-out tasks enter their quiescent states > quickly. I noticed this when I was testing trampoline callback execution. > > To test the trampoline freeing, I wrote a simple script: > cd /sys/kernel/debug/tracing/ > echo '__schedule_bug:traceon' > set_ftrace_filter; > echo '!__schedule_bug:traceon' > set_ftrace_filter; > > In the background I had simple bash while loop: > while [ 1 ]; do x=1; done & > > Total time of completion of above commands in seconds: > > With this patch: > real 0m0.179s > user 0m0.000s > sys 0m0.054s > > Without this patch: > real 0m1.098s > user 0m0.000s > sys 0m0.053s > > That's a great than 6X speed up in performance. In order to accomplish > this, I am waiting for HZ/10 time before entering the hold-out checking > loop. The loop still preserves its checking of held tasks every 1 second > as before, incase this first test doesn't succeed. > > Cc: Steven Rostedt <rostedt@goodmis.org>
Seems straightforward enough. The commit log needs a bit of cleanup ("atleast", "great than", ...).
Steve, thoughts? Any reason why this would be a problem?
Thanx, Paul
> Cc: Peter Zilstra <peterz@infradead.org> > Cc: Ingo Molnar <mingo@redhat.com> > Cc: Boqun Feng <boqun.feng@gmail.com> > Cc: Paul McKenney <paulmck@linux.vnet.ibm.com> > Cc: byungchul.park@lge.com > Cc: kernel-team@android.com > Signed-off-by: Joel Fernandes (Google) <joel@joelfernandes.org> > --- > Changes since v1->v2: > - Changed total wait time to HZ/10 instead of 2 jiffies > - Updated the commands to reproduce issue > > kernel/rcu/update.c | 12 +++++++++++- > 1 file changed, 11 insertions(+), 1 deletion(-) > > diff --git a/kernel/rcu/update.c b/kernel/rcu/update.c > index 5783bdf86e5a..a28698e44b08 100644 > --- a/kernel/rcu/update.c > +++ b/kernel/rcu/update.c > @@ -743,6 +743,12 @@ static int __noreturn rcu_tasks_kthread(void *arg) > */ > synchronize_srcu(&tasks_rcu_exit_srcu); > > + /* > + * Wait a little bit incase held tasks are released > + * during their next timer ticks. > + */ > + schedule_timeout_interruptible(HZ/10); > + > /* > * Each pass through the following loop scans the list > * of holdout tasks, removing any that are no longer > @@ -755,7 +761,6 @@ static int __noreturn rcu_tasks_kthread(void *arg) > int rtst; > struct task_struct *t1; > > - schedule_timeout_interruptible(HZ); > rtst = READ_ONCE(rcu_task_stall_timeout); > needreport = rtst > 0 && > time_after(jiffies, lastreport + rtst); > @@ -768,6 +773,11 @@ static int __noreturn rcu_tasks_kthread(void *arg) > check_holdout_task(t, needreport, &firstreport); > cond_resched(); > } > + > + if (list_empty(&rcu_tasks_holdouts)) > + break; > + > + schedule_timeout_interruptible(HZ); > } > > /* > -- > 2.17.0.441.gb46fe60e1d-goog >
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