Re: [Qemu-devel] [PATCH v7] docs: add cpu-hotplug.txt

[Alexandre DERUMIER]

Hello,

I'm looking to implement cpu hotplug,

and I have a question about cpu flags

currently I have something like

-cpu qemu64,+lahf_lm,+sep,+kvm_pv_unhalt,+kvm_pv_eoi,enforce
-smp 4,sockets=2,cores=2,maxcpus=4


Does I need to define flags like:

-smp 2,sockets=2,cores=2,maxcpus=4
-device 
qemu64-x86_64-cpu,+lahf_lm,+sep,+kvm_pv_unhalt,+kvm_pv_eoi,enforce,id=cpu1,socket-id=1,core-id=1,thread-id=0
 
... 

?


Another question,
is -smp mandatory ?  (if I want coldplug all cpus)

-smp sockets=2,cores=2,maxcpus=4
-device qemu64-x86_64-cpu,id=cpu1,socket-id=1,core-id=1,thread-id=0 
-device qemu64-x86_64-cpu,id=cpu1,socket-id=1,core-id=2,thread-id=0 
-device qemu64-x86_64-cpu,id=cpu3,socket-id=2,core-id=1,thread-id=0 
-device qemu64-x86_64-cpu,id=cpu4,socket-id=2,core-id=2,thread-id=0 

or does I need minimum 1 non unplugable cpu

-smp 1,sockets=2,cores=2,maxcpus=4
-device qemu64-x86_64-cpu,id=cpu1,socket-id=1,core-id=2,thread-id=0 
-device qemu64-x86_64-cpu,id=cpu3,socket-id=2,core-id=1,thread-id=0 
-device qemu64-x86_64-cpu,id=cpu4,socket-id=2,core-id=2,thread-id=0 



Regards,

Alexandre



----- Mail original -----
De: "Dou Liyang" <address@hidden>
À: "qemu-devel" <address@hidden>
Cc: "Dou Liyang" <address@hidden>, address@hidden, "ehabkost" <address@hidden>, 
"Markus Armbruster" <address@hidden>, address@hidden, "Fam Zheng" 
<address@hidden>, "Igor Mammedov" <address@hidden>, address@hidden
Envoyé: Jeudi 18 Août 2016 03:50:50
Objet: [Qemu-devel] [PATCH v7] docs: add cpu-hotplug.txt

This document describes how to use cpu hotplug in QEMU. 

Signed-off-by: Dou Liyang <address@hidden> 
Reviewed-by: Andrew Jones <address@hidden> 
--- 
Change log v6 -> v7 
>From Bharata's advice 
1. add "qom_path" property explanation for 
"info hotpluggable-cpus" command 
>From drew's advice 
1. Fix some spelling mistake 

Change log v5 -> v6 
>From drew's advice 
1. Fix some spelling and grammar mistakes 

Change log v4 -> v5 
1. add an example for sPAPR 
>From Bharata's advice 
1. Fix the examples 

Change log v3 -> v4 
>From David's advice 
1. add spapr examples 
2. Fix some comment 
>From drew's advice 
1. Fix some syntax 

Change log v2 -> v3: 
>From drew's advice: 
1. modify the examples. 
2. Fix some syntax. 

Change log v1 -> v2: 
>From Fam's advice: 
1. Fix some comment. 

Change log v1: 
>From Igor's advice: 
1. Remove any mentioning of apic-id from the document. 
2. Remove the "device_del qom_path" from the CPU hot-unplug. 
3. Fix some comment. 

docs/cpu-hotplug.txt | 156 +++++++++++++++++++++++++++++++++++++++++++++++++++ 
1 file changed, 156 insertions(+) 
create mode 100644 docs/cpu-hotplug.txt 

diff --git a/docs/cpu-hotplug.txt b/docs/cpu-hotplug.txt 
new file mode 100644 
index 0000000..3667641 
--- /dev/null 
+++ b/docs/cpu-hotplug.txt 
@@ -0,0 +1,156 @@ 
+QEMU CPU hotplug 
+================ 
+ 
+This document explains how to use the CPU hotplug feature in QEMU, 
+which regards the CPU as a device, using -device/device_add and 
+device_del. 
+ 
+QEMU support was merged for 2.7. 
+ 
+Guest support is required for CPU hotplug to work. 
+ 
+CPU hot-plug 
+------------ 
+ 
+In order to be able to hotplug CPUs, QEMU has to be told the maximum 
+number of CPUs which the guest can have. This is done at startup time 
+by means of the -smp command-line option, which has the following 
+format: 
+ 
+ -smp [cpus=]n[,maxcpus=cpus][,cores=cores][,threads=threads] 
+ [,sockets=sockets] 
+ 
+where, 
+ 
+ - "cpus" sets the number of CPUs to 'n' [default=1]. 
+ - "maxcpus" sets the maximum number of CPUs, including offline VCPUs 
+ for hotplug. 
+ - "sockets" sets the number of discrete sockets in the system. 
+ - "cores" sets the number of CPU cores on one socket. 
+ - "threads" sets the number of threads on one CPU core. 
+ 
+For example, the following command-line: 
+ 
+ qemu [...] -smp 4,maxcpus=8,sockets=2,cores=2,threads=2 
+ 
+creates a guest with 4 VCPUs and supports up to 8 VCPUs. The CPU topology 
+is sockets (2) * cores (2) * threads (2) and should compute a number of 
+slots exactly equal to maxcpus. A computed number of slots greater than 
+maxcpus will result in error. When the guest finishes loading, the guest 
+will see 4 VCPUs. More of this below. 
+ 
+Query available CPU objects 
+--------------------------- 
+ 
+To add a VCPU, it must be identified by socket-id, core-id, and/or 
+thread-id parameters. 
+ 
+Before adding the VCPU, we should know the topology parameters, so 
+that we can find the available location (socket,core,thread) for a 
+new VCPU. 
+ 
+Use the HMP command "info hotpluggable-cpus" to obtain them, for example: 
+ 
+ (qemu) info hotpluggable-cpus 
+ 
+lists all CPUs including the present and possible hot-pluggable CPUs. 
+Such as this: 
+ 
+ ... 
+ type: "qemu64-x86_64-cpu" 
+ vcpus_count: "1" 
+ CPUInstance Properties: 
+ socket-id: "1" 
+ core-id: "0" 
+ thread-id: "0" 
+ type: "qemu64-x86_64-cpu" 
+ vcpus_count: "1" 
+ qom_path: "/machine/unattached/device[4]" 
+ CPUInstance Properties: 
+ socket-id: "0" 
+ core-id: "1" 
+ thread-id: "1" 
+ ... 
+ 
+or 
+ 
+ ... 
+ type: "POWER7_v2.3-spapr-cpu-core" 
+ vcpus_count: "1" 
+ CPUInstance Properties: 
+ core-id: "2" 
+ type: "POWER7_v2.3-spapr-cpu-core" 
+ vcpus_count: "1" 
+ qom_path: "/machine/unattached/device[2]" 
+ CPUInstance Properties: 
+ core-id: "1" 
+ ... 
+ 
+The property called "qom_path" indicates that the listed CPU is already 
+present or plugged-in. 
+ 
+Different platforms may have different "CPUInstance Properties", which 
+will be used in hot-plugging below. 
+ 
+Hotplug CPUs 
+------------ 
+ 
+A monitor command may be used to hotplug CPUs: 
+ 
+ - "device_add": creates a CPU device and inserts it into the 
+ specific location. 
+ 
+For example, the following command adds a VCPU, which has the id cpu1, 
+to a specific location in the topology (socket=1,core=0,thread=0): 
+ 
+ (qemu) device_add qemu64-x86_64-cpu,id=cpu1,socket-id=1,core-id=0,thread-id=0 
+ 
+where, 
+ 
+ - "qemu64-x86_64-cpu" is the CPU model. 
+ - "id" is the unique identifier in the device set. 
+ - "socket-id/core-id/thread-id" represent the designated location, 
+ which is obtained from the above possible list of CPUs. 
+ 
+It's also possible to start a guest with a CPU cold-plugged into a 
+specific location (socket,core,thread). 
+ 
+In the following command line example, a guest which has 4 VCPUs is 
+created: 
+ 
+ qemu [...] -smp 2,maxcpus=8,sockets=2,cores=2,threads=2 \ 
+ -device qemu64-x86_64-cpu,id=cpu1,socket-id=1,\ 
+ core-id=1,thread-id=0 \ 
+ -device qemu64-x86_64-cpu,id=cpu2,socket-id=1,\ 
+ core-id=1,thread-id=1 \ 
+ 
+Two VCPUs are cold-plugged by the "-device" parameter, which are in 
+the same socket and core, but with different thread-ids. After that, 
+the guest has an additional four VCPUs available for hot-plug when 
+needed. 
+ 
+The above example is for an x86 machine type. The topology parameters 
+and resulting number of online VCPUs may not be suitable for other 
+platforms. The "CPUInstance Properties" output described above lists 
+the valid topology parameters. 
+ 
+For example, the following command adds a VCPU in an sPAPR hardware 
+system: 
+ 
+ (qemu) device_add POWER7_v2.3-spapr-cpu-core,id=cpu1,core-id=2 
+ 
+CPU hot-unplug 
+-------------- 
+ 
+In order to be able to hot unplug a CPU device, QEMU removes the 
+device by using the id which was assigned when hotplugging it. 
+ 
+A monitor command may be used to hot unplug CPUs: 
+ 
+ - "device_del": deletes a CPU device 
+ 
+For example, assuming that the CPU device with id "cpu1" exists, 
+then the following command tries to remove it. 
+ 
+ (qemu) device_del cpu1 
+ 
-- 
2.5.5