On Fri-10/24/14-2014 10:20, Paul E. McKenney wrote:
> 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.
Doesn't seem to make a difference here
> 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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