* QEMU online/offline cpu
@ 2017-01-02 20:27 ` Ozgur O Kilic
0 siblings, 0 replies; 4+ messages in thread
From: Ozgur O Kilic @ 2017-01-02 20:27 UTC (permalink / raw)
To: kvm, qemu-devel
Hi
I am trying to understand how QEMU threads respond to set a vCPU online or offline.
Specifically, what happens to QEMU thread if in the guest, we execute:
echo 0 > /sys/devices/system/cpu/cpu1/online
Is the corresponding QEMU thread paused?
Thank you
Ozgur Ozan Kilic
^ permalink raw reply [flat|nested] 4+ messages in thread
* [Qemu-devel] QEMU online/offline cpu
@ 2017-01-02 20:27 ` Ozgur O Kilic
0 siblings, 0 replies; 4+ messages in thread
From: Ozgur O Kilic @ 2017-01-02 20:27 UTC (permalink / raw)
To: kvm, qemu-devel
Hi
I am trying to understand how QEMU threads respond to set a vCPU online or offline.
Specifically, what happens to QEMU thread if in the guest, we execute:
echo 0 > /sys/devices/system/cpu/cpu1/online
Is the corresponding QEMU thread paused?
Thank you
Ozgur Ozan Kilic
^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: [Qemu-devel] QEMU online/offline cpu
2017-01-02 20:27 ` [Qemu-devel] " Ozgur O Kilic
(?)
@ 2017-01-03 11:37 ` Igor Mammedov
2017-01-09 17:10 ` Igor Mammedov
-1 siblings, 1 reply; 4+ messages in thread
From: Igor Mammedov @ 2017-01-03 11:37 UTC (permalink / raw)
To: Ozgur O Kilic; +Cc: kvm, qemu-devel, Peter Krempa
On Mon, 2 Jan 2017 23:27:50 +0300
Ozgur O Kilic <okilic1@binghamton.edu> wrote:
> Hi
>
> I am trying to understand how QEMU threads respond to set a vCPU online or offline.
>
> Specifically, what happens to QEMU thread if in the guest, we execute:
>
> echo 0 > /sys/devices/system/cpu/cpu1/online
> Is the corresponding QEMU thread paused?
on success CPU executes play_dead() and isn't used/scheduled by guest.
However it's still possible to online it back using
echo 1 > /sys/devices/system/cpu/cpu1/online
If you need to prevent that happening you should use QEMU's
device_del command via HMP/QMP interface.
For x86 it would trigger ACPI based CPU hot-unplug action after which
vCPU object in QMEU would be destroyed and corresponding KVM thread
be parked and corresponding CPU object /sys/devices/system/cpu/cpuXX
in guest is removed. To use that CPU again in guest, one should
hotplug it back in QEMU using device_add.
details of ACPI based cpu hot(un)plug qemu<->guest protocol are described in
QEMU/docs/specs/acpi_cpu_hotplug.txt file. x86 ACPI based implementation is
mostly contained in QEMU/hw/acpi/cpu* files.
Wiki page http://wiki.qemu.org/Features/CPUHotplug is rather outdated,
I'll update it to reflect currently implemented hotplug interfaces/targets.
PS:
cpu hot-unplug is recently new feature so one should use recent
qemu/libvirt versions.
> Thank you
> Ozgur Ozan Kilic
^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: [Qemu-devel] QEMU online/offline cpu
2017-01-03 11:37 ` Igor Mammedov
@ 2017-01-09 17:10 ` Igor Mammedov
0 siblings, 0 replies; 4+ messages in thread
From: Igor Mammedov @ 2017-01-09 17:10 UTC (permalink / raw)
To: Ozgur O Kilic; +Cc: Peter Krempa, qemu-devel, kvm, David Gibson
On Tue, 3 Jan 2017 12:37:36 +0100
Igor Mammedov <imammedo@redhat.com> wrote:
[...]
> Wiki page http://wiki.qemu.org/Features/CPUHotplug is rather outdated,
> I'll update it to reflect currently implemented hotplug interfaces/targets.
David,
I've updated above CPUHotplug wiki page to match current state of QEMU.
Could you take a look at it and maybe update from SPAPR perspective.
PS:
Feel free to fix whatever if you find a better wording/mistake.
^ permalink raw reply [flat|nested] 4+ messages in thread
end of thread, other threads:[~2017-01-09 17:10 UTC | newest]
Thread overview: 4+ messages (download: mbox.gz / follow: Atom feed)
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2017-01-02 20:27 QEMU online/offline cpu Ozgur O Kilic
2017-01-02 20:27 ` [Qemu-devel] " Ozgur O Kilic
2017-01-03 11:37 ` Igor Mammedov
2017-01-09 17:10 ` Igor Mammedov
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