Re: [Qemu-devel] strange situation, guest cpu thread spinning at ~100%, but display not yet initialized

[Chris Friesen]

On 11/2/2018 2:45 PM, Chris Friesen wrote:
> On 11/2/2018 11:51 AM, Dr. David Alan Gilbert wrote:

> >     so the fix is Fam's 'aio: Do aio_notify_accept only during blocking
> > aio_poll'.  I see you're running the qemu-kvm-ev from centos, if I read
> > the version tea-leaves right, then I think that patch is in the
> > 2.10.0-21.el7_5.7.1 package I can see.
>
> It looks like we do not have this fix in our code, will definitely be 
> giving it a try.
Well, it appears that this was not the fix.  With the patches applied we 
still saw the problem.

One of my coworkers has been investigating further, and he sent me the 
following information:

"One of the things the BIOS does before initializing the VGA is to start 
the CPUs. More specifically, from CPU-0, it broadcasts a Setup 
InterProcess Interrupt (SIPI) to all the remaining processors so that 
they wake up and are initialized. CPU-0 busy-waits for all the 
Instance’s CPUs to be initialized, and once that happens, it moves on to 
continue booting (which includes initializing the VGA).  In our case, 
one CPU fails to respond to the SIPI causing CPU-0 to keep busy waiting 
for it. I am in the process of adding more instrumentation to qemu so 
that we can know whether the missing CPU did not receive the SIPI or 
what happened."

Chris