On 09/14/2016 03:19 PM, Linus Torvalds wrote:
> On Wed, Sep 14, 2016 at 12:14 PM, Waiman Long<waiman.long@hpe.com>  wrote:
>> In the stack backtrace above, the kernel hadn't even reached SMP boot after
>> about 50s. That was extremely slow. I tried the 4.7.3 kernel and it booted
>> up fine. So I suspect that there may be too many interrupts going on and it
>> consumes most of the CPU cycles. The prime suspect is the random driver, I
>> think.
> Any chance of bisecting it at least partially? The random driver
> doesn't do interrupts itself, it just gets called by other drivers
> doing intterrupts. So if there are too many of them, that would be
> something else..
>
>                 Linus

I have finally finished bisecting the problem. I was wrong in saying 
that the 4.7.3 kernel had no problem. It did have. There were some 
slight differences between the 4.8 and 4.7 kernel config files that I 
used. After some further testing, it was found that the bootup problem 
only happened when the following kernel config option was defined:

CONFIG_EFI_MIXED=y

Bisecting reviewed that the following 4.6 patch was the first patch that 
had this problem:

c9f2a9a65e4855b74d92cdad688f6ee4a1a323ff
[PATCH] x86/efi: Hoist page table switching code into efi_call_virt()

I did testing on my test system with three different partition sizes:
1) 16-socket Broadwell-EX with 12TB memory
2) 8-socket Broadwell-EX with 6TB memory
3) 4-socket Broadwell-EX with 3TB memory

Only the 16-socket and 8-socket configurations had this problem. I am 
not sure if over 4TB of main memory is a factor or not.

I have attached several slightly different panic messages that had 
happened in my testing. I know little about the EFI code and so I am not 
sure if it is a kernel problem, firmware problem or a combination of 
both. Hopefully someone with knowledge on this code will shed light on 
this problem.

Cheers,
Longman