Re: [kvm-devel] Second KVM process hangs eating 80-100% CPU on host during startup

[Alex D. <ale...@ya...>]

--- On Fri, 4/18/08, Avi Kivity <av...@qu...> wrote:

> From: Avi Kivity <av...@qu...>
> Subject: Re: [kvm-devel] Second KVM process hangs eating 80-100% CPU on host during startup
> To: "Alex Davis" <ale...@ya...>
> Cc: kvm...@li...
> Date: Friday, April 18, 2008, 12:12 PM
> Alex Davis wrote:
> > Host software:
> > Linux 2.6.24.4
> > KVM 65 (I am using the kernel modules from this
> release).
> > X11 7.2 from Xorg
> > SDL 1.2.13
> > GCC 4.1.1
> > Glibc 2.4
> >
> > Host hardware:
> > Asus P5B Deluxe (P965 chipset based) motherboard
> > 4 GB RAM
> > Intel E6700 CPU
> >
> > Guest software:
> > Slackware 12.0 installed from CD-ROM.
> >
> > Command used to first KVM instance:
> > /usr/local/bin/qemu-system-x86_64 -hda
> /spare/vdisk1.img -cdrom /dev/cdrom -boot c -m 384 -net
> > nic,macaddr=DE:AD:BE:EF:11:29 -net
> tap,ifname=tap0,script=no &
> >
> > Command used to start second KVM instance:
> > /usr/local/bin/qemu-system-x86_64 -hda
> /spare/vdisk2.img -cdrom /dev/cdrom -boot c -m 384 -net
> > nic,macaddr=DE:AD:BE:EF:11:30 -net
> tap,ifname=tap1,script=no &
> >
> > tap0 and tap1 are bridged on the host. The guest OS
> was installed on /spare/vdisk1.img, 
> > which was initially created by /usr/local/bin/qemu-img
> create -f qcow /spare/vdisk.img 10G
> > After the guest installation completed, vdisk1 was
> copied to vdisk2.
> >
> > The second instance always stops after printing
> > Checking if the processor honours the WP bit even in
> supervisor mode... Ok.
> > It stays hung until I press the return key in the
> first instance; sometimes clicking in another X
> > window will wake it up as well. 
> >
> > This is a test machine so I can test patches (almost)
> at will.
> >
> >   
> 
> Strange.  Does pinning each guest to a different cpu help
> (use 'taskset 
> 1 qemu ... vdisk1.img &  ', taskset 2 qemu ...
> vdisk2.img)

Some additional information:

I upgraded the guest to 2.6.25, and added some printk's to init_32.c and
init/calibrate.c in the kernel source tree. Here's the output from dmesg
for the guest boot:

[    0.004000] Checking if this processor honours the WP bit even in supervisor mode...Ok.
[    0.004000] Before cpa_init.
[    0.004000] CPA: page pool initialized 1 of 1 pages preallocated
[    0.004000] After cpa_init.
[    0.004000] After pagealloc
[    0.004000] After cpu_hotplug_init
[    0.004000] After kmem_cache_init
[    0.004000] After setup_percpu_pageset
[    0.004000] After numa_policy_init
[    0.004005] After late_time_init
[    0.004622] Before read_current_timer(&pre_start)
[    0.005314] After read_current_timer()
[    0.006493] Before read_current_timer(&start)
[   16.065027] Before read_current_timer(&post_start)  
[   16.065753] Before read_current_timer(&post_end)
[   16.066437] Before read_current_timer(&start)
[   16.073007] Before read_current_timer(&post_start)
[   16.081007] Before read_current_timer(&post_end)
[   16.081703] Before read_current_timer(&start)
[   16.089008] Before read_current_timer(&post_start)
[   16.097008] Before read_current_timer(&post_end)
[   16.097695] Before read_current_timer(&start)
[   16.105010] Before read_current_timer(&post_start)
[   16.113009] Before read_current_timer(&post_end)
[   16.113697] Before read_current_timer(&start)
[   16.121010] Before read_current_timer(&post_start)
[   16.129010] Before read_current_timer(&post_end)
[   16.129697] calibrate_delay_direct() failed to get a good estimate for loops_per_jiffy.
[   16.129698] Probably due to long platform interrupts. Consider using "lpj=" boot option.
[   16.132180] Calibrating delay loop... 5308.41 BogoMIPS (lpj=10616832)
[   16.237019] After calibrate_delay



Notice how the time jumped from about 0 seconds to 16 seconds. That's where I woke it up by typing in another window. The code seems to be hanging in the call to read_current_timer(&start) in function calibrate_delay_direct in init/calibrate.c. Also notice that 
calibrate_delay_direct() failed.




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