Re: Slow Kernel Boot

[Izik Eidus <izike-atKUWr5tajBWk0Htik3J/w@public.gmane.org>]

Dave Hansen wrote:
> On Tue, 2008-01-08 at 00:16 +0200, Izik Eidus wrote:
>   
>> Dave Hansen wrote:
>>     
>>> With kvm-44, I thought my kernel was freezing during boot if I gave it
>>> 1G of RAM.  But, it boots fine with 512M.
>>>
>>> So, I instrumented the kernel, and found out that it is just taking a
>>> long time to memset a 58MB area of memory for mem_map[].  It appears to
>>> be taking a mmio_exit for every access of every byte of memory.  The end
>>> result is a ~100kbps memset() speed.  Yes, 100 kilobytes/sec.
>>>
>>> I just tried kvm from git, and the kernel doesn't even get that far.  I
>>> see this in debugfs
>>>  
>>> 	insn_emulation:1393985
>>>
>>> even before I get a single kernel message.  And it keeps going up, fast.
>>> I can get the kernel to boot just fine if I give it less than 896MB of
>>> RAM.
>>>
>>> kvm-44 boots long enough for me to see a really funky e820 table:
>>>
>>> BIOS-provided physical RAM map:
>>>  BIOS-e820: 0000000000000000 - 000000000009fc00 (usable)
>>>  BIOS-e820: 000000000009fc00 - 00000000000a0000 (reserved)
>>>  BIOS-e820: 00000000000e8000 - 0000000000100000 (reserved)
>>>  BIOS-e820: 0000000000100000 - 00000000fffbd000 (usable)
>>>  BIOS-e820: 00000000fffbd000 - 00000000ffff0000 (reserved)
>>>
>>> Note that this is with '-m 1G'!!  It looks to me like one of those
>>> sections is basically from 0x100000 up to ~4G and *usable*.  That
>>> doesn't look right.
>>>   
>>>       
>> yea it really dont look right, it look like it for some reason map the 
>> whole memory up untill the bios to the kernel as memory
>> it even map it on the pci hole so...
>> hrmmm, very weird,
>>
>> what is your host info (32/64 amd/intel kernel...)?
>>     
>
> 64-bit intel host, kernel 2.6.24-rc5
>
> Running kvm's current git userspace with modules from the same version.
>
>   
>> and what is the 
>> guest info (kernel 32/64...) ?
>>     
>
> 32-bit 2.6.23-rc6-mm1
>
>   
>> and what happen if you run it with -no-kvm ?
>>     
>
> Both current -git and kvm-44 seem to lock up at early kernel boot before
> even early printk is available.  But, GRUB comes up in both cases. 
>
> -no-kvm doesn't seem to change things at all.
>
> -- Dave
>
>   
when you see the grub how much memory is it saying you have?
how can i get the image that you are using?
(i dont know if it will be too much to ask, but if you run it with pure 
qemu (from qemu.org) is it working?)

for some reason the e820 return a really false values for your guest...
i would have suggest to check if you have the latest kvm bios(not in 
your physical computer bios) but it cannot be the problem as that you 
dont run it with more than 3.something giga...

i am going to sleep now, i will look at this tomorrow (this is strange)

thanks for reporting

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