Messages in this thread | | | Date | Sat, 8 Aug 2009 16:56:34 -0700 | From | "Paul E. McKenney" <> | Subject | Re: CONFIG_PREEMPT_RCU in next/mmotm |
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On Sat, Aug 08, 2009 at 08:34:03PM +0100, Hugh Dickins wrote: > Hi Paul, > > Is CONFIG_PREEMPT_RCU=y expected to be working in -next (or mmotm)? > > I ask because it appears to break down on PowerPC G5 when I try two > "make -j20" kernel builds in parallel. The "filp" slab which usually > contains a couple of thousand objects or so, jumps up to a couple of > hundred thousand before the builds complete, and continues rising > from then on - I think that's a sign of RCU in disgrace? > And rebooting hangs thereafter.
That would indeed be bad.
> And I notice that include/linux/rcupreempt.h currently says: > static inline void synchronize_rcu_expedited(void) > { > synchronize_rcu(); /* Placeholder for new rcupreempt implementation. */ > } > which gives an impression of work in progress?
Yep, but I would be surprised if this was causing your problem. In fact, I would be surprised if this function was being invoked. Then again, I have been surprised more than once.
For whatever it is worth, with luck, include/linux/rcupreempt.h disappears entirely at some point.
> CONFIG_PREEMPT_TREE=y seems okay on PowerPC; and when I briefly tried
CONFIG_TREE_RCU=y, you mean, right?
> CONFIG_PREEMPT_RCU=y on x86_64, it didn't show above symptoms there.
Interesting...
> I did try bisecting yesterday's linux-next git, but that led me to > > commit 8ca17c6082feee5841a7b0e91d00e18c3f85f063 > Merge: dafcc6e... 7256cf0... > Author: Ingo Molnar <mingo@elte.hu> > Date: Mon Aug 3 15:50:37 2009 +0200 > > Merge branch 'core/rcu' into auto-sched-next > > rather than to any particular patch of yours which that merges: > which seemed odd, but I'm not accustomed to bisecting next.
I honestly don't know how "git bisect" interacts with merges.
> Another odd thing is that mmotm .DATE=2009-07-30-05-01, the last > I tried before Thursday's, showed no such symptoms: yet appears to > contain all the larger RCU changes, just lacking some more recent > on/offline race fixes. I didn't notice any likely difference > between those mmotm trees down in arch/powerpc either. > > My guess is that there's some other issue which is triggering > the RCU disgrace, but that is just a guess.
The one other issue I know of is one that apparently happens only on one of Ingo's machines, which suddenly decides that it need not inform RCU when onlining a CPU (at boot time).
But you seem to be making it past boot, and I would guess that you are not doing any hotplug CPU operations, right?
> Config attached. Any suggestions?
/me scratches head... Will try some more CONFIG_PREEMPT_RCU testing locally.
Thanx, Paul
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