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Groups > linux.kernel > #1534371
| From | Peter Zijlstra <peterz@infradead.org> |
|---|---|
| Newsgroups | linux.kernel |
| Subject | Re: INFO: rcu_sched detected stalls on CPUs/tasks with `kswapd` and `mem_cgroup_shrink_node` |
| Date | 2016-12-01 19:20 +0100 |
| Message-ID | <sJE7E-85V-39@gated-at.bofh.it> (permalink) |
| References | (5 earlier) <sJkLD-2XW-11@gated-at.bofh.it> <sJsg9-7Ys-1@gated-at.bofh.it> <sJyYh-3Vi-9@gated-at.bofh.it> <sJCyS-6te-35@gated-at.bofh.it> <sJCSe-6Dp-3@gated-at.bofh.it> |
| Organization | linux.* mail to news gateway |
On Thu, Dec 01, 2016 at 08:59:18AM -0800, Paul E. McKenney wrote:
> On Thu, Dec 01, 2016 at 05:36:14PM +0100, Peter Zijlstra wrote:
> > Well, with the above change cond_resched() is already sufficient, no?
>
> Maybe. Right now, cond_resched_rcu_qs() gets a quiescent state to
> the RCU core in less than one jiffy, with my other change, this becomes
> a handful of jiffies depending on HZ and NR_CPUS. I expect this
> increase to a handful of jiffies to be a non-event.
>
> After my upcoming patch, cond_resched() will get a quiescent state to
> the RCU core in about ten seconds. While I am am not all that nervous
> about the increase from less than a jiffy to a handful of jiffies,
> increasing to ten seconds via cond_resched() does make me quite nervous.
> Past experience indicates that someone's kernel will likely be fatally
> inconvenienced by this magnitude of change.
>
> Or am I misunderstanding what you are proposing?
No, that is indeed what I was proposing. Hurm.. OK let me ponder that a
bit. There might be a few games we can play with !PREEMPT to avoid IPIs.
Thing is, I'm slightly uncomfortable with de-coupling rcu-sched from
actual schedule() calls.
> > In fact, by doing the IPI thing we get the entire cond_resched*()
> > family, and we could add the should_resched() guard to
> > cond_resched_rcu().
>
> So that cond_resched_rcu_qs() looks something like this, in order
> to avoid the function call in the case where the scheduler has nothing
> to do?
I was actually thinking of this:
diff --git a/include/linux/sched.h b/include/linux/sched.h
index 2d0c82e1d348..2dc7d8056b2a 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -3374,9 +3374,11 @@ static inline int signal_pending_state(long state, struct task_struct *p)
static inline void cond_resched_rcu(void)
{
#if defined(CONFIG_DEBUG_ATOMIC_SLEEP) || !defined(CONFIG_PREEMPT_RCU)
- rcu_read_unlock();
- cond_resched();
- rcu_read_lock();
+ if (should_resched(1)) {
+ rcu_read_unlock();
+ cond_resched();
+ rcu_read_lock();
+ }
#endif
}
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Re: INFO: rcu_sched detected stalls on CPUs/tasks with `kswapd` and `mem_cgroup_shrink_node` Donald Buczek <buczek@molgen.mpg.de> - 2016-11-27 10:20 +0100
Re: INFO: rcu_sched detected stalls on CPUs/tasks with `kswapd` and `mem_cgroup_shrink_node` Michal Hocko <mhocko@kernel.org> - 2016-11-28 12:10 +0100
Re: INFO: rcu_sched detected stalls on CPUs/tasks with `kswapd` and `mem_cgroup_shrink_node` Paul Menzel <pmenzel@molgen.mpg.de> - 2016-11-28 13:30 +0100
Re: INFO: rcu_sched detected stalls on CPUs/tasks with `kswapd` and `mem_cgroup_shrink_node` Donald Buczek <buczek@molgen.mpg.de> - 2016-11-30 11:30 +0100
Re: INFO: rcu_sched detected stalls on CPUs/tasks with `kswapd` and `mem_cgroup_shrink_node` Michal Hocko <mhocko@kernel.org> - 2016-11-30 12:20 +0100
Re: INFO: rcu_sched detected stalls on CPUs/tasks with `kswapd` and `mem_cgroup_shrink_node` Donald Buczek <buczek@molgen.mpg.de> - 2016-11-30 12:50 +0100
Re: INFO: rcu_sched detected stalls on CPUs/tasks with `kswapd` and `mem_cgroup_shrink_node` Donald Buczek <buczek@molgen.mpg.de> - 2016-12-02 10:20 +0100
Re: INFO: rcu_sched detected stalls on CPUs/tasks with `kswapd` and `mem_cgroup_shrink_node` Donald Buczek <buczek@molgen.mpg.de> - 2016-12-06 09:40 +0100
Re: INFO: rcu_sched detected stalls on CPUs/tasks with `kswapd` and `mem_cgroup_shrink_node` "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2016-11-30 13:00 +0100
Re: INFO: rcu_sched detected stalls on CPUs/tasks with `kswapd` and `mem_cgroup_shrink_node` Paul Menzel <pmenzel@molgen.mpg.de> - 2016-11-30 13:40 +0100
Re: INFO: rcu_sched detected stalls on CPUs/tasks with `kswapd` and `mem_cgroup_shrink_node` "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2016-11-30 15:40 +0100
Re: INFO: rcu_sched detected stalls on CPUs/tasks with `kswapd` and `mem_cgroup_shrink_node` "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2016-11-30 13:00 +0100
Re: INFO: rcu_sched detected stalls on CPUs/tasks with `kswapd` and `mem_cgroup_shrink_node` Michal Hocko <mhocko@kernel.org> - 2016-11-30 14:20 +0100
Re: INFO: rcu_sched detected stalls on CPUs/tasks with `kswapd` and `mem_cgroup_shrink_node` "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2016-11-30 15:40 +0100
Re: INFO: rcu_sched detected stalls on CPUs/tasks with `kswapd` and `mem_cgroup_shrink_node` Peter Zijlstra <peterz@infradead.org> - 2016-11-30 17:40 +0100
Re: INFO: rcu_sched detected stalls on CPUs/tasks with `kswapd` and `mem_cgroup_shrink_node` Michal Hocko <mhocko@kernel.org> - 2016-11-30 18:10 +0100
Re: INFO: rcu_sched detected stalls on CPUs/tasks with `kswapd` and `mem_cgroup_shrink_node` "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2016-11-30 18:30 +0100
Re: INFO: rcu_sched detected stalls on CPUs/tasks with `kswapd` and `mem_cgroup_shrink_node` Michal Hocko <mhocko@kernel.org> - 2016-11-30 18:40 +0100
Re: INFO: rcu_sched detected stalls on CPUs/tasks with `kswapd` and `mem_cgroup_shrink_node` Peter Zijlstra <peterz@infradead.org> - 2016-11-30 19:00 +0100
Re: INFO: rcu_sched detected stalls on CPUs/tasks with `kswapd` and `mem_cgroup_shrink_node` "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2016-11-30 22:40 +0100
Re: INFO: rcu_sched detected stalls on CPUs/tasks with `kswapd` and `mem_cgroup_shrink_node` Peter Zijlstra <peterz@infradead.org> - 2016-12-01 06:40 +0100
Re: INFO: rcu_sched detected stalls on CPUs/tasks with `kswapd` and `mem_cgroup_shrink_node` "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2016-12-01 13:50 +0100
Re: INFO: rcu_sched detected stalls on CPUs/tasks with `kswapd` and `mem_cgroup_shrink_node` Peter Zijlstra <peterz@infradead.org> - 2016-12-01 17:40 +0100
Re: INFO: rcu_sched detected stalls on CPUs/tasks with `kswapd` and `mem_cgroup_shrink_node` "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2016-12-01 18:00 +0100
Re: INFO: rcu_sched detected stalls on CPUs/tasks with `kswapd` and `mem_cgroup_shrink_node` Peter Zijlstra <peterz@infradead.org> - 2016-12-01 19:20 +0100
Re: INFO: rcu_sched detected stalls on CPUs/tasks with `kswapd` and `mem_cgroup_shrink_node` "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2016-12-01 19:50 +0100
Re: INFO: rcu_sched detected stalls on CPUs/tasks with `kswapd` and `mem_cgroup_shrink_node` Peter Zijlstra <peterz@infradead.org> - 2016-12-01 20:00 +0100
Re: INFO: rcu_sched detected stalls on CPUs/tasks with `kswapd` and `mem_cgroup_shrink_node` "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2016-11-30 18:10 +0100
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