On Fri, Oct 24, 2014 at 08:09:31PM +0300, Yanko Kaneti wrote:
> On Fri-10/24/14-2014 09:54, Paul E. McKenney wrote:
> > On Fri, Oct 24, 2014 at 07:29:43PM +0300, Yanko Kaneti wrote:
> > > On Fri-10/24/14-2014 08:40, Paul E. McKenney wrote:
> > > > On Fri, Oct 24, 2014 at 12:08:57PM +0300, Yanko Kaneti wrote:
> > > > > On Thu-10/23/14-2014 15:04, Paul E. McKenney wrote:
> > > > > > On Fri, Oct 24, 2014 at 12:45:40AM +0300, Yanko Kaneti wrote:
> > > > > > >
> > > > > > > On Thu, 2014-10-23 at 13:05 -0700, Paul E. McKenney wrote:
> > > > > > > > On Thu, Oct 23, 2014 at 10:51:59PM +0300, Yanko Kaneti wrote:
> >
> > [ . . . ]
> >
> > > > > Ok, unless I've messsed up something major, bisecting points to:
> > > > >
> > > > > 35ce7f29a44a rcu: Create rcuo kthreads only for onlined CPUs
> > > > >
> > > > > Makes any sense ?
> > > >
> > > > Good question. ;-)
> > > >
> > > > Are any of your online CPUs missing rcuo kthreads? There should be
> > > > kthreads named rcuos/0, rcuos/1, rcuos/2, and so on for each online CPU.
> > >
> > > Its a Phenom II X6. With 3.17 and linux-tip with 35ce7f29a44a reverted,
> > > the rcuos are 8
> > > and the modprobe ppp_generic testcase reliably works, libvirt also manages
> > > to setup its bridge.
> > >
> > > Just with linux-tip , the rcuos are 6 but the failure is as reliable as
> > > before.
>
> > Thank you, very interesting. Which 6 of the rcuos are present?
>
> Well, the rcuos are 0 to 5. Which sounds right for a 6 core CPU like this
> Phenom II.
Ah, you get 8 without the patch because it creates them for potential
CPUs as well as real ones. OK, got it.
> > > Awating instructions: :)
> >
> > Well, I thought I understood the problem until you found that only 6 of
> > the expected 8 rcuos are present with linux-tip without the revert. ;-)
> >
> > I am putting together a patch for the part of the problem that I think
> > I understand, of course, but it would help a lot to know which two of
> > the rcuos are missing. ;-)
>
> Ready to test
Well, if you are feeling aggressive, give the following patch a spin.
I am doing sanity tests on it in the meantime.
Thanx, Paul
------------------------------------------------------------------------
diff --git a/kernel/rcu/tree_plugin.h b/kernel/rcu/tree_plugin.h
index 29fb23f33c18..927c17b081c7 100644
--- a/kernel/rcu/tree_plugin.h
+++ b/kernel/rcu/tree_plugin.h
@@ -2546,9 +2546,13 @@ static void rcu_spawn_one_nocb_kthread(struct rcu_state
*rsp, int cpu)
rdp->nocb_leader = rdp_spawn;
if (rdp_last && rdp != rdp_spawn)
rdp_last->nocb_next_follower = rdp;
- rdp_last = rdp;
- rdp = rdp->nocb_next_follower;
- rdp_last->nocb_next_follower = NULL;
+ if (rdp == rdp_spawn) {
+ rdp = rdp->nocb_next_follower;
+ } else {
+ rdp_last = rdp;
+ rdp = rdp->nocb_next_follower;
+ rdp_last->nocb_next_follower = NULL;
+ }
} while (rdp);
rdp_spawn->nocb_next_follower = rdp_old_leader;
}
--
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