[Xen-devel] xl vcpu-set <guest> <nr> does not work properly.

[Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>]

When I try this with the "SeaBIOS" QEMU it does not hotplug
all of the CPUs and it complains about the existing ones:

-bash-4.1# xl vcpu-list
Name                                ID  VCPU   CPU State   Time(s) CPU
Affinity
Domain-0                             0     0    1   -b-      87.1  any
cpu
Domain-0                             0     1    2   -b-      14.4  any
cpu
Domain-0                             0     2    3   -b-      11.0  any
cpu
Domain-0                             0     3    0   r--      13.7  any
cpu
latest                               7     0    3   -b-      10.9  any
cpu
latest                               7     1    0   -b-       1.7  any
cpu
latest                               7     2    -   --p       0.0  any
cpu
latest                               7     3    -   --p       0.0  any
cpu
-bash-4.1# xl vcpu-set 7 4
libxl: error: libxl_qmp.c:287:qmp_handle_error_response: received an
error message from QMP server: Unable to add CPU: 0, it already exists
libxl: error: libxl_qmp.c:287:qmp_handle_error_response: received an
error message from QMP server: Unable to add CPU: 1, it already exists
-bash-4.1# xl vcpu-list
Name                                ID  VCPU   CPU State   Time(s) CPU
Affinity
Domain-0                             0     0    0   -b-      87.4  any
cpu
Domain-0                             0     1    3   -b-      14.6  any
cpu
Domain-0                             0     2    2   -b-      11.1  any
cpu
Domain-0                             0     3    1   r--      13.7  any
cpu
latest                               7     0    2   -b-      11.7  any
cpu
latest                               7     1    1   -b-       1.7  any
cpu
latest                               7     2    3   -b-       0.0  any
cpu

And sure enough - in the guest it only added one CPU:

[   85.720139] CPU2 has been hot-added
[   85.726409] installing Xen timer for CPU 2
[   85.735674] smpboot: Booting Node 0 Processor 2 APIC 0x4
[   85.755080] cpu 2 spinlock event irq 86
[   85.763671] microcode: CPU2 sig=0x206a7, pf=0x2, revision=0x28
[   85.770669] Will online and init hotplugged CPU: 2

Perhaps the SeaBIOS/new qemu needs variants of:

f62079c piix4acpi, xen, hotplug: Fix race with ACPI AML code and hotplug.
e28e062 piix4acpi, xen: Clarify that the qemu_set_irq calls just do an IRQ 
pulse.
2133c38 piix4acpi, xen, vcpu hotplug: Split the notification from the changes

Thanks!

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