[Bug 65081] New: Starting a second guest with -smp 2 makes the first guest very slow and the second one hang (or also very slow)

[Bug 65081] New: Starting a second guest with -smp 2 makes the first guest very slow and the second one hang (or also very slow)

[bugzilla-daemon]

https://bugzilla.kernel.org/show_bug.cgi?id=65081

            Bug ID: 65081
           Summary: Starting a second guest with -smp 2 makes the first
                    guest very slow and the second one hang (or also very
                    slow)
           Product: Virtualization
           Version: unspecified
    Kernel Version: 3.12
          Hardware: All
                OS: Linux
              Tree: Mainline
            Status: NEW
          Severity: normal
          Priority: P1
         Component: kvm
          Assignee: virtualization_kvm@kernel-bugs.osdl.org
          Reporter: d.haid@gogi.tv
        Regression: No

I think this first occured when I upgraded the kernel to 3.11 and qemu to
1.6.1. I am now running kernel version 3.12 and the problem still exists.

If I start a first KVM guest with -smp 2 it runs fine. As soon as I start
another KVM guest on the same host also with -smp 2, the first one gets
extremely slow. I can type one character per second via ssh. I do not see any
messages from the second guest, so it seems to hang or is very slow.

If I start the second kVM guest without -smp 2 both guests seem to work fine.

I get the following messages on the host, but I do not know whether they are
relevant.

kvm: SMP vm created on host with unstable TSC; guest TSC will not be reliable

qemu-system-x86: sending ioctl 5326 to a partition!
qemu-system-x86: sending ioctl 80200204 to a partition!

kvm [409]: vcpu0 unhandled rdmsr: 0xc0010001
kvm [409]: vcpu0 unhandled rdmsr: 0x3a

-

It is likely that this is not enough information to find the bug, so I would
appreciate any help on what I can do to obtain more information about what
might be happening here.

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[Bug 65081] Starting a second guest with -smp 2 makes the first guest very slow and the second one hang (or also very slow)

[bugzilla-daemon]

https://bugzilla.kernel.org/show_bug.cgi?id=65081

--- Comment #1 from Daniel Haid <d.haid@gogi.tv> ---
I have been told that I should provide the command line I am using, so here it
is:

qemu-system-x86_64 -enable-kvm -kernel vmlinuz-linux -initrd
initramfs-linux.img -append "console=ttyS0,57600 loglevel=7 root=/dev/vda rw"
-nographic -m 512 -drive file=/dev/mapper/vg0-xxxx--root,if=virtio -drive
file=/dev/mapper/vg0-xxxx--swap,if=virtio -net nic,model=virtio -net
tap,name=tap0,ifname=tap0,script=no,downscript=no -smp 2

The xxxx is different for the two guests.

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[Bug 65081] Starting a second guest with -smp 2 makes the first guest very slow and the second one hang (or also very slow)

[bugzilla-daemon]

https://bugzilla.kernel.org/show_bug.cgi?id=65081

--- Comment #2 from Daniel Haid <d.haid@gogi.tv> ---
The problem persists with linux 3.14.1 and qemu 1.7.1.

Any suggestions on which further information you need is very welcome.

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[Bug 65081] Starting a second guest with -smp 2 makes the first guest very slow and the second one hang (or also very slow)

[bugzilla-daemon]

https://bugzilla.kernel.org/show_bug.cgi?id=65081

--- Comment #3 from Daniel Haid <d.haid@gogi.tv> ---
I removed all unnecessary arguments. The following command line is actually
sufficient to produce hanging guests:

qemu-system-x86_64 -enable-kvm -kernel vmlinuz-linux -initrd
initramfs-linux.img -append "console=ttyS0,57600" -nographic -smp 2

I tried to run multiple guests and found out the following: It is possible to
run multiple non-smp-guests (I tried three) and one smp-guest fine. But as soon
as a second smp-guest is started, both smp-guests hang. However, the
non-smp-guests are not affected!

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[Bug 65081] Starting a second guest with -smp 2 makes the first guest very slow and the second one hang (or also very slow)

[bugzilla-daemon]

https://bugzilla.kernel.org/show_bug.cgi?id=65081

Daniel Haid <d.haid@gogi.tv> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
     Kernel Version|3.12                        |3.14

--- Comment #4 from Daniel Haid <d.haid@gogi.tv> ---
I have now tried and seen that using -no-kvm-irqchip actually solves the
problem.

Some more information about the bug:

Instead of two "-smp 2" guests, one "-smp 3" (or higher) guest will also hang.

And note that when running the two guests, they are running as different users.
How can they ever be allowed to influence each other?

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[Bug 65081] Starting a second guest with -smp 2 makes the first guest very slow and the second one hang (or also very slow)

[bugzilla-daemon]

https://bugzilla.kernel.org/show_bug.cgi?id=65081

--- Comment #5 from Daniel Haid <d.haid@gogi.tv> ---
The problem seems to be fixed with linux 3.19 and qemu 2.2.1.

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[Bug 65081] Starting a second guest with -smp 2 makes the first guest very slow and the second one hang (or also very slow)

[bugzilla-daemon]

https://bugzilla.kernel.org/show_bug.cgi?id=65081

Paolo Bonzini <bonzini@gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |RESOLVED
                 CC|                            |bonzini@gnu.org
         Resolution|---                         |CODE_FIX

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