Re: Arndale secondary CPU boot issue Was Re: [xen-unstable test] 60076: regressions - FAIL

[Andrew Cooper <andrew.cooper3@citrix.com>]

On 29/07/15 19:18, Julien Grall wrote:
> On 29/07/15 15:15, Julien Grall wrote:
>>>> Can it be that things are "just" slow, since we're creating a 4 vcpus
>>>> guest on a 1 pcpu (not so powerful, I guess) host?
>>> The arndale board has a 2 physical CPUs. Although it looks like that the
>>> secondary cpu is never coming up:
>>>
>>> Jul 28 01:35:39.057076 (XEN) Adding cpu 1 to runqueue 0
>>> Jul 28 01:35:39.057104 (XEN) Bringing up CPU1
>>> Jul 28 01:35:39.064998 (XEN) CPU1 never came online
>>> Jul 28 01:35:40.065133 (XEN) Removing cpu 1 from runqueue 0
>>> Jul 28 01:35:40.065176 (XEN) Failed to bring up CPU 1 (error -5)
>>>
>>> This has been broken at some point in Xen 4.6. Xen 4.5 is booting with
>>> the right number of physical on the Arndale.
> I figured out what's going on. The problem interestingly came after the
> commit which added the support of the ticket lock [1] in Xen.
>
> While the problem is solved by reverting this patch, the source of the
> issue is not because of a ticket lock issue with ARM (thanks god!).

As an aside, why is failing to bring up a cpu not fatal under ARM?

I admit that x86 isn't much better in this regard - it will spin in an
infinite loop waiting for the upcoming cpu to call in, but it least it
doesn't proceed booting with some cpus unexpectedly missing.

~Andrew