Re: [Xen-devel] Xen 4.8 + Linux 4.9 + Credit2 = can't bootup

[Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>]

On 01/04/2017 09:10 PM, Konrad Rzeszutek Wilk wrote:
> On Wed, Jan 04, 2017 at 08:52:03PM -0500, Konrad Rzeszutek Wilk wrote:
> > Hey,
> >
> > I was trying to bootup on an 30 CPU machine (15 core, SMT).
> >
> > It works just fine with credit1 (see further down the log)
> > but if I try credit2 it ends up hanging during bootup.
> >
> > I am a going to naively assume it is due to how the vCPUs are
> > exposed (Where they match the physical CPUs under credit1),
> > but under credit2 they are different.
> >
> > The dom0_max_vcpus does not seem to have any affect. When I remove it
> > things are still being problematic.
> >
> > Help!?
> It seems now that I took dom0_max_vcpus out of the picture I can
> reproduce this with credit1 scheduler. So it looks like an Linux issue.
>
> Boris, any ideas? This is 4.9.
I think 4.9 is broken. There were changes in topology initialization 
that broke Xen in early 4.9 RCs. tglx posted a patch that resolved this 
issue (he was actually addressing something else and fixing dom0 crash 
was a side effect). I thought it would make it to 4.9 but apparently it 
didn't: I just tried 4.9 with default Xen scheduler and it crashed. Not 
with the error that you are seeing though:
...
[   41.327438] cpu 31 spinlock event irq 327
[   41.386455] x86: Booted up 1 node, 32 CPUs
[   41.400223] BUG: arch topology borken
[   41.412415]      the SMT domain not a subset of the MC domain
...
[   42.375375] BUG: arch topology borken
[   42.387665]      the SMT domain not a subset of the MC domain
[   42.412511] divide error: 0000 [#1] SMP
[   42.424831] Modules linked in:
[   42.435129] CPU: 1 PID: 2 Comm: kthreadd Not tainted 4.9.0 #66
[   42.454579] Hardware name: Intel Corporation S2600CP/S2600CP, BIOS 
SE5C600.86B.99.99.x032.072520111118 07/25/2011
[   42.488610] task: ffff8808143a0dc0 task.stack: ffffc90004240000
[   42.508346] RIP: e030:[<ffffffff810cfe4b>]  [<ffffffff810cfe4b>] 
select_task_rq_fair+0x2fb/0x730
...

Latest 4.10-rc2 boots both credit1 and credit2. So you can either try 
that or apply 9d85eb9119f4eeeb48e87adfcd71f752655700e9, which I think is 
the missing patch.
-boris

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