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Re: INFO: rcu_sched detected stalls on CPUs/tasks with `kswapd` and `mem_cgroup_shrink_node`

From Michal Hocko <mhocko@kernel.org>
Newsgroups linux.kernel
Subject Re: INFO: rcu_sched detected stalls on CPUs/tasks with `kswapd` and `mem_cgroup_shrink_node`
Date 2016-11-30 18:10 +0100
Message-ID <sJgyl-s0-13@gated-at.bofh.it> (permalink)
References (5 earlier) <sJb5D-5oB-7@gated-at.bofh.it> <sJbIl-5Bx-15@gated-at.bofh.it> <sJcXL-6zu-1@gated-at.bofh.it> <sJedc-7iT-25@gated-at.bofh.it> <sJg5j-8ux-9@gated-at.bofh.it>
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On Wed 30-11-16 17:38:20, Peter Zijlstra wrote:
> On Wed, Nov 30, 2016 at 06:29:55AM -0800, Paul E. McKenney wrote:
> > We can, and you are correct that cond_resched() does not unconditionally
> > supply RCU quiescent states, and never has.  Last time I tried to add
> > cond_resched_rcu_qs() semantics to cond_resched(), I got told "no",
> > but perhaps it is time to try again.
> 
> Well, you got told: "ARRGH my benchmark goes all regress", or something
> along those lines. Didn't we recently dig out those commits for some
> reason or other?
> 
> Finding out what benchmark that was and running it against this patch
> would make sense.
> 
> Also, I seem to have missed, why are we going through this again?

Well, the point I've brought that up is because having basically two
APIs for cond_resched is more than confusing. Basically all longer in
kernel loops do cond_resched() but it seems that this will not help the
silence RCU lockup detector in rare cases where nothing really wants to
schedule. I am really not sure whether we want to sprinkle
cond_resched_rcu_qs at random places just to silence RCU detector...

-- 
Michal Hocko
SUSE Labs

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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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