kernel bootup slow issue on ovm3.1.1

["zhenzhong.duan" <zhenzhong.duan@oracle.com>]

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Hi maintainers,

We meet a uek2 bootup slow issue on our ovm product(ovm3.0.3 and ovm3.1.1).

The system env is an exalogic node with 24 cores + 100G mem (2 socket ,
6 cores per socket, 2 HT threads per core).
After boot up this node with all cores enabled,
We boot a pvhvm with 12vpcus (or 24) + 90 GB + pci passthroughed device,
it takes 30+ mins to boot.
If we remove passthrough device from vm.cfg, bootup takes about 2 mins.
If we use a small mem(eg. 10G + 24 vcpus), bootup takes about 3 mins.
So a big mem + passthrough device made the worst case.

If we boot this node with HT disabled from BIOS. Now only 12 cores are
available.
OVM on same node, same config with 12vpcus+90GB boots in 1.5 mins!

After some debug, we found it's in kernel mtrr init that make this delay.

mtrr_aps_init() 
 \-> set_mtrr() 
     \-> mtrr_work_handler() 

kernel spin in mtrr_work_handler.

But we don't know the scene hide in the hypervisor. Why big mem +
passthrough made the worst case.
Is this already fixed in xen upstream?
Any comments are welcome, I'll upload all data depend on your need.

thanks
zduan

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