Re: [PATCH v2 6/8] kvm tools: Add rwlock wrapper

[Sasha Levin <levinsasha928@gmail.com>]

On Fri, 2011-06-03 at 09:34 +0200, Ingo Molnar wrote:
> * Sasha Levin <levinsasha928@gmail.com> wrote:
> 
> > > with no apparent progress being made.
> > 
> > Since it's something that worked in 2.6.37, I've looked into it to 
> > find what might have caused this issue.
> > 
> > I've bisected guest kernels and found that the problem starts with:
> > 
> > a26ac2455ffcf3be5c6ef92bc6df7182700f2114 is the first bad commit
> > commit a26ac2455ffcf3be5c6ef92bc6df7182700f2114
> > Author: Paul E. McKenney <paul.mckenney@linaro.org>
> > Date:   Wed Jan 12 14:10:23 2011 -0800
> > 
> >     rcu: move TREE_RCU from softirq to kthread
> > 
> > Ingo, could you confirm that the problem goes away for you when you 
> > use an earlier commit?
> 
> testing will have to wait, but there's a recent upstream fix:
> 
>   d72bce0e67e8: rcu: Cure load woes
> 
> That *might* perhaps address this problem too.
> 
I've re-tested with Linus's current git, the problem is still there.

> If not then this appears to be some sort of RCU related livelock with 
> brutally overcommitted vcpus. On native this would show up too, in a 
> less drastic form, as a spurious bootup delay.

I don't think it was overcommited by *that* much. With that commit it
usually hangs at 20-40 vcpus, while without it I can go up to 255.

-- 

Sasha.