Re: Slow Kernel Boot

[Dave Hansen <haveblue-r/Jw6+rmf7HQT0dZR+AlfA@public.gmane.org>]

On Tue, 2008-01-08 at 00:46 +0200, Izik Eidus wrote:
> 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?

    GNU GRUB  version 0.97  (639K lower / 4193279K upper memory)

> how can i get the image that you are using?

The disk images?  I made them myself and I've been using them for quite
a while.  Probably a year or more.

> (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?)

Ahhh.  I'm using the ubuntu one, and it does the same thing.  I guess
that means I found a qemu bug.

> 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...

Yeah, I just updated the BIOSes.  They're right out of KVM's git repo.

-- Dave


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