[Qemu-devel] [PATCH 0/4 v8 for-1.5] target-i386: CPU hot-add with cpu-add QMP command

[Qemu-devel] [PATCH 0/4 v8 for-1.5] target-i386: CPU hot-add with cpu-add QMP command

[Igor Mammedov]

Implements alternative way for hot-adding CPU using cpu-add QMP command,
which could be useful until it would be possible to add CPUs via device_add.

To hot-add CPU use following command from qmp-shell:
 cpu-add id=[0..max-cpus - 1)

git tree for testing: https://github.com/imammedo/qemu/tree/cpu_add.v8

based on qom-cpu tree

v8->v7:
  * skip already applied patches
  * split adding hot_add_cpu hook into separate function
  * add cpu-model machine option and use QemuOpts for getting it
    during CPU hotplug.

v7->v6:
  * skip already applied patches
  * rename icc-bus instance name to "icc"
  * pass icc_bridge from board as argument down CPU creation call chain,
    instead of dynamically resolving it for each CPU.

v6->v5:
  * override hot_add_cpu hook statically
  * extend and use memory_region_find() in IOAPIC
  * s/signal_cpu_creation/tcg_signal_cpu_creation/
  * add "since 1.5 to cpu-addQAPI schema description

v5->v4:
  * style fixes
  * new helper qemu_for_each_cpu()
  * switch to qemu_for_each_cpu() in cpu_exists()
  * "pc: update rtc ..." patch make depend it on "mc146818rtc: QOM'ify"
    and use QOM cast style
  * call CPU added notifier right before CPU becomes runable
  * s/resume_vcpu/cpu_resume/
  * acpi/piix4: add spec documentation for QEMU<->Seabios CPU hotplug
    interface
  * use error_propagate() in pc_new_cpu()
  * skip cpu_exists() check in apic-id property setter if new value is
    the same as current
  * embed icc-bus inside icc-bridge and use qbus_create_inplace()
  * move include/hw/i386/icc_bus.h into include/hw/cpu/
  * make missing icc-bus fatal error for softmmu target
  * split "move APIC to ICC bus" and "move IOAPIC to ICC bus" on smaller
    patches
  * use qdev_get_parent_bus() to get parent bus
  * split "add cpu-add command..." on smaller patches

v4->v3:
  * 'id' in cpu-add command will be a thread number instead of APIC ID
  * split off resume_vcpu() into separate patch
  * move notifier from rtc code into pc.c

v2->v3:
  * use local error & propagate_error() instead of operating on
    passed in errp in several places
  * replace CPUClass.get_firmware_id() with CPUClass.get_arch_id()
  * leave IOAPIC creation to board and just set bus to icc-bus
  * include kvm-stub.o in cpu libary if no KVM is configured
  * create resume_vcpu() stub and include it in libqemustub,
    and use it directly instead of CPU method
  * acpi_piix4: s/cpu_add_notifier/cpu_added_notifier/

v1->v2:
  * generalize cpu sync to KVM, resume and hot-plug notification and
    invoke them form CPUClass, to make available to all targets.
  * introduce cpu_exists() and CPUClass.get_firmware_id() and use
    the last one in acpi_piix to make code target independent.
  * move IOAPIC to ICC bus, it was suggested and easy to convert.
  * leave kvmvapic as SysBusDevice, it doesn't affect hot-plug and
    created only once for all APIC instances. I haven't found yet
    good/clean enough way to convert it to ICCDevice. May be follow-up
    though.
  * split one big ICC patch into several, one per converted device
  * add cpu_hot_add hook to machine and implement it for target-i386,
    instead of adding stabs. Could be used by other targets to
    implement cpu-add.
  * pre-allocate links<CPU> for all possible CPUs and make them available
    at /machine/icc-bridge/cpu[0..N] QOM path, so users could find out
    possible/free CPU IDs to use in cpu-add command.


Igor Mammedov (4):
  add hot_add_cpu hook to QEMUMachine
  QMP: add cpu-add command
  add cpu-model option to -machine
  target-i386: implement machine->hot_add_cpu hook

 hw/i386/pc.c         | 29 +++++++++++++++++++++++++++++
 hw/i386/pc_piix.c    |  1 +
 hw/i386/pc_q35.c     |  1 +
 include/hw/boards.h  |  1 +
 include/hw/i386/pc.h |  1 +
 qapi-schema.json     | 13 +++++++++++++
 qmp-commands.hx      | 23 +++++++++++++++++++++++
 qmp.c                | 10 ++++++++++
 vl.c                 | 12 +++++++++++-
 9 files changed, 90 insertions(+), 1 deletion(-)

-- 
1.8.2.1

[Qemu-devel] [PATCH 1/4] add hot_add_cpu hook to QEMUMachine

[Igor Mammedov]

hot_add_cpu hook should be overriden by target that implements
cpu hot-add via cpu-add QMP command.

Signed-off-by: Igor Mammedov <imammedo@redhat.com>
---
Note:
  hook will be used in next patch for target-i386 cp-add implementation.
---
 include/hw/boards.h | 1 +
 1 file changed, 1 insertion(+)

diff --git a/include/hw/boards.h b/include/hw/boards.h
index 425bdc7..75cd127 100644
--- a/include/hw/boards.h
+++ b/include/hw/boards.h
@@ -43,6 +43,7 @@ typedef struct QEMUMachine {
     GlobalProperty *compat_props;
     struct QEMUMachine *next;
     const char *hw_version;
+    void (*hot_add_cpu)(const int64_t id, Error **errp);
 } QEMUMachine;
 
 int qemu_register_machine(QEMUMachine *m);
-- 
1.8.2.1

[Qemu-devel] [PATCH 2/4] QMP: add cpu-add command

[Igor Mammedov]

Adds "cpu-add id=xxx" QMP command.

cpu-add's "id" argument is a CPU number in a range [0..max-cpus)

Example QMP command:
 -> { "execute": "cpu-add", "arguments": { "id": 2 } }
 <- { "return": {} }

Signed-off-by: Igor Mammedov <imammedo@redhat.com>
Acked-by: Luiz Capitulino <lcapitulino@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
---
v7:
  * added "Since 1.5" to cpu-add qapi schema definition
v6:
  * added valid values description to qapi schema
  * split out cpu_hot_add hooks introduction into separate patch
  * split out implementation of cpu_hot_add for target-i386
v5:
  * accept id=[0..max_cpus) range in cpu-add command
v4:
  * merge "qmp: add cpu-add qmp command" & "target-i386: implement CPU hot-add" patches
  * move notifier call to CPUCLass.realize()
  * add hook cpu_hot_add to QEMUMachine
  * make QEMUMachineInitArgs global and keep default cpu_model there

v3:
  * it appears that 'online/offline' in cpu-set are confusing people
    with what command actually does and users might have to distinguish
    if 'offline' is not implemented by parsing error message. To simplify
    things replace cpu-set with cpu-add command to show more clear what
    command does and just add cpu-del when CPU remove is implemented.

v2:
  * s/cpu_set/cpu-set/
  * qmp doc style fix
  * use bool type instead of opencodding online/offline string
     suggested-by: Eric Blake <eblake@redhat.com>
---
 qapi-schema.json | 13 +++++++++++++
 qmp-commands.hx  | 23 +++++++++++++++++++++++
 qmp.c            | 10 ++++++++++
 3 files changed, 46 insertions(+)

diff --git a/qapi-schema.json b/qapi-schema.json
index 5b0fb3b..6f58b0f 100644
--- a/qapi-schema.json
+++ b/qapi-schema.json
@@ -1387,6 +1387,19 @@
 { 'command': 'cpu', 'data': {'index': 'int'} }
 
 ##
+# @cpu-add
+#
+# Adds CPU with specified ID
+#
+# @id: ID of CPU to be created, valid values [0..max_cpus)
+#
+# Returns: Nothing on success
+#
+# Since 1.5
+##
+{ 'command': 'cpu-add', 'data': {'id': 'int'} }
+
+##
 # @memsave:
 #
 # Save a portion of guest memory to a file.
diff --git a/qmp-commands.hx b/qmp-commands.hx
index 0e89132..ed99eb8 100644
--- a/qmp-commands.hx
+++ b/qmp-commands.hx
@@ -385,6 +385,29 @@ Note: CPUs' indexes are obtained with the 'query-cpus' command.
 EQMP
 
     {
+        .name       = "cpu-add",
+        .args_type  = "id:i",
+        .mhandler.cmd_new = qmp_marshal_input_cpu_add,
+    },
+
+SQMP
+cpu-add
+-------
+
+Adds virtual cpu
+
+Arguments:
+
+- "id": cpu id (json-int)
+
+Example:
+
+-> { "execute": "cpu-add", "arguments": { "id": 2 } }
+<- { "return": {} }
+
+EQMP
+
+    {
         .name       = "memsave",
         .args_type  = "val:l,size:i,filename:s,cpu:i?",
         .mhandler.cmd_new = qmp_marshal_input_memsave,
diff --git a/qmp.c b/qmp.c
index ed6c7ef..dd34be6 100644
--- a/qmp.c
+++ b/qmp.c
@@ -24,6 +24,7 @@
 #include "hw/qdev.h"
 #include "sysemu/blockdev.h"
 #include "qom/qom-qobject.h"
+#include "hw/boards.h"
 
 NameInfo *qmp_query_name(Error **errp)
 {
@@ -108,6 +109,15 @@ void qmp_cpu(int64_t index, Error **errp)
     /* Just do nothing */
 }
 
+void qmp_cpu_add(int64_t id, Error **errp)
+{
+    if (current_machine->hot_add_cpu) {
+        current_machine->hot_add_cpu(id, errp);
+    } else {
+        error_setg(errp, "Not supported");
+    }
+}
+
 #ifndef CONFIG_VNC
 /* If VNC support is enabled, the "true" query-vnc command is
    defined in the VNC subsystem */
-- 
1.8.2.1

[Qemu-devel] [PATCH 3/4] add cpu-model option to -machine

[Igor Mammedov]

Provides globally accessible cpu-model via machine opts.

Signed-off-by: Igor Mammedov <imammedo@redhat.com>
---
Note:
 - it will be used in cpu-add hook on tartget-i386.
---
 vl.c | 12 +++++++++++-
 1 file changed, 11 insertions(+), 1 deletion(-)

diff --git a/vl.c b/vl.c
index 1e7d474..37a0f81 100644
--- a/vl.c
+++ b/vl.c
@@ -429,6 +429,10 @@ static QemuOptsList qemu_machine_opts = {
             .name = "usb",
             .type = QEMU_OPT_BOOL,
             .help = "Set on/off to enable/disable usb",
+        }, {
+            .name = "cpu-model",
+            .type = QEMU_OPT_STRING,
+            .help = "alias for \"-cpu\"  CPU model definition",
         },
         { /* End of list */ }
     },
@@ -2979,7 +2983,7 @@ int main(int argc, char **argv, char **envp)
             }
             case QEMU_OPTION_cpu:
                 /* hw initialization will check this */
-                cpu_model = optarg;
+                qemu_opts_set(qemu_find_opts("machine"), 0, "cpu-model", optarg);
                 break;
             case QEMU_OPTION_hda:
                 {
@@ -3919,6 +3923,11 @@ int main(int argc, char **argv, char **envp)
      */
     cpudef_init();
 
+    machine_opts = qemu_opts_find(qemu_find_opts("machine"), 0);
+    if (machine_opts) {
+        cpu_model = qemu_opt_get(machine_opts, "cpu-model");
+    }
+
     if (cpu_model && is_help_option(cpu_model)) {
         list_cpus(stdout, &fprintf, cpu_model);
         exit(0);
@@ -4124,6 +4133,7 @@ int main(int argc, char **argv, char **envp)
         kernel_filename = qemu_opt_get(machine_opts, "kernel");
         initrd_filename = qemu_opt_get(machine_opts, "initrd");
         kernel_cmdline = qemu_opt_get(machine_opts, "append");
+        cpu_model = qemu_opt_get(machine_opts, "cpu-model");
     } else {
         kernel_filename = initrd_filename = kernel_cmdline = NULL;
     }
-- 
1.8.2.1

[Qemu-devel] [PATCH 4/4] target-i386: implement machine->hot_add_cpu hook

[Igor Mammedov]

Signed-off-by: Igor Mammedov <imammedo@redhat.com>
---
v3:
  * use machine.cpu-model option to store default value and to
    get current value when hot-adding CPU
v2:
  * override .hot_add_cpu staticaly starting with 1.5 machine
---
 hw/i386/pc.c         | 29 +++++++++++++++++++++++++++++
 hw/i386/pc_piix.c    |  1 +
 hw/i386/pc_q35.c     |  1 +
 include/hw/i386/pc.h |  1 +
 4 files changed, 32 insertions(+)

diff --git a/hw/i386/pc.c b/hw/i386/pc.c
index 6b3faac..b7d28d6 100644
--- a/hw/i386/pc.c
+++ b/hw/i386/pc.c
@@ -54,6 +54,7 @@
 #include "qemu/config-file.h"
 #include "hw/acpi/acpi.h"
 #include "hw/cpu/icc_bus.h"
+#include "hw/boards.h"
 
 /* debug PC/ISA interrupts */
 //#define DEBUG_IRQ
@@ -915,6 +916,33 @@ static X86CPU *pc_new_cpu(const char *cpu_model, int64_t apic_id,
     return cpu;
 }
 
+void pc_hot_add_cpu(const int64_t id, Error **errp)
+{
+    DeviceState *icc_bridge;
+    const char *cpu_model;
+    QemuOpts *machine_opts;
+    int64_t apic_id = x86_cpu_apic_id_from_index(id);
+
+    if (cpu_exists(apic_id)) {
+        error_setg(errp, "Unable to add CPU: %" PRIi64
+                   ", it already exists", id);
+        return;
+    }
+
+    if (id >= max_cpus) {
+        error_setg(errp, "Unable to add CPU: %" PRIi64
+                   ", max allowed: %d", id, max_cpus - 1);
+        return;
+    }
+
+    machine_opts = qemu_opts_find(qemu_find_opts("machine"), 0);
+    cpu_model = qemu_opt_get(machine_opts, "cpu-model");
+
+    icc_bridge = DEVICE(object_resolve_path_type("icc-bridge",
+                                                 TYPE_ICC_BRIDGE, NULL));
+    pc_new_cpu(cpu_model, apic_id, icc_bridge, errp);
+}
+
 void pc_cpus_init(const char *cpu_model, DeviceState *icc_bridge)
 {
     int i;
@@ -928,6 +956,7 @@ void pc_cpus_init(const char *cpu_model, DeviceState *icc_bridge)
 #else
         cpu_model = "qemu32";
 #endif
+        qemu_opts_set(qemu_find_opts("machine"), 0, "cpu-model", cpu_model);
     }
 
     for (i = 0; i < smp_cpus; i++) {
diff --git a/hw/i386/pc_piix.c b/hw/i386/pc_piix.c
index 2190f0a..8e1d179 100644
--- a/hw/i386/pc_piix.c
+++ b/hw/i386/pc_piix.c
@@ -325,6 +325,7 @@ static QEMUMachine pc_i440fx_machine_v1_5 = {
     .alias = "pc",
     .desc = "Standard PC (i440FX + PIIX, 1996)",
     .init = pc_init_pci,
+    .hot_add_cpu = pc_hot_add_cpu,
     .max_cpus = 255,
     .is_default = 1,
     DEFAULT_MACHINE_OPTIONS,
diff --git a/hw/i386/pc_q35.c b/hw/i386/pc_q35.c
index a926e38..fe44087 100644
--- a/hw/i386/pc_q35.c
+++ b/hw/i386/pc_q35.c
@@ -214,6 +214,7 @@ static QEMUMachine pc_q35_machine_v1_5 = {
     .alias = "q35",
     .desc = "Standard PC (Q35 + ICH9, 2009)",
     .init = pc_q35_init,
+    .hot_add_cpu = pc_hot_add_cpu,
     .max_cpus = 255,
     DEFAULT_MACHINE_OPTIONS,
 };
diff --git a/include/hw/i386/pc.h b/include/hw/i386/pc.h
index 8a6e76c..0bbb7b4 100644
--- a/include/hw/i386/pc.h
+++ b/include/hw/i386/pc.h
@@ -79,6 +79,7 @@ void pc_register_ferr_irq(qemu_irq irq);
 void pc_acpi_smi_interrupt(void *opaque, int irq, int level);
 
 void pc_cpus_init(const char *cpu_model, DeviceState *icc_bridge);
+void pc_hot_add_cpu(const int64_t id, Error **errp);
 void pc_acpi_init(const char *default_dsdt);
 void *pc_memory_init(MemoryRegion *system_memory,
                     const char *kernel_filename,
-- 
1.8.2.1

Re: [Qemu-devel] [PATCH 3/4] add cpu-model option to -machine

[Eduardo Habkost]

On Tue, Apr 30, 2013 at 08:34:02AM +0200, Igor Mammedov wrote:
> Provides globally accessible cpu-model via machine opts.
> 
> Signed-off-by: Igor Mammedov <imammedo@redhat.com>

Reviewed-by: Eduardo Habkost <ehabkost@redhat.com>

It looks like most data on QEMUMachineInitArgs is already present on
machine_opts. Maybe we could add machine_opts to QEMUMachineInitArgs and
gradually remove existing QEMUMachineInitArgs fields?


> ---
> Note:
>  - it will be used in cpu-add hook on tartget-i386.
> ---
>  vl.c | 12 +++++++++++-
>  1 file changed, 11 insertions(+), 1 deletion(-)
> 
> diff --git a/vl.c b/vl.c
> index 1e7d474..37a0f81 100644
> --- a/vl.c
> +++ b/vl.c
> @@ -429,6 +429,10 @@ static QemuOptsList qemu_machine_opts = {
>              .name = "usb",
>              .type = QEMU_OPT_BOOL,
>              .help = "Set on/off to enable/disable usb",
> +        }, {
> +            .name = "cpu-model",
> +            .type = QEMU_OPT_STRING,
> +            .help = "alias for \"-cpu\"  CPU model definition",
>          },
>          { /* End of list */ }
>      },
> @@ -2979,7 +2983,7 @@ int main(int argc, char **argv, char **envp)
>              }
>              case QEMU_OPTION_cpu:
>                  /* hw initialization will check this */
> -                cpu_model = optarg;
> +                qemu_opts_set(qemu_find_opts("machine"), 0, "cpu-model", optarg);
>                  break;
>              case QEMU_OPTION_hda:
>                  {
> @@ -3919,6 +3923,11 @@ int main(int argc, char **argv, char **envp)
>       */
>      cpudef_init();
>  
> +    machine_opts = qemu_opts_find(qemu_find_opts("machine"), 0);
> +    if (machine_opts) {
> +        cpu_model = qemu_opt_get(machine_opts, "cpu-model");
> +    }
> +
>      if (cpu_model && is_help_option(cpu_model)) {
>          list_cpus(stdout, &fprintf, cpu_model);
>          exit(0);
> @@ -4124,6 +4133,7 @@ int main(int argc, char **argv, char **envp)
>          kernel_filename = qemu_opt_get(machine_opts, "kernel");
>          initrd_filename = qemu_opt_get(machine_opts, "initrd");
>          kernel_cmdline = qemu_opt_get(machine_opts, "append");
> +        cpu_model = qemu_opt_get(machine_opts, "cpu-model");
>      } else {
>          kernel_filename = initrd_filename = kernel_cmdline = NULL;
>      }
> -- 
> 1.8.2.1
> 

-- 
Eduardo

Re: [Qemu-devel] [PATCH 2/4] QMP: add cpu-add command

[Eduardo Habkost]

(CCing libvir-list)

On Tue, Apr 30, 2013 at 08:34:01AM +0200, Igor Mammedov wrote:
> Adds "cpu-add id=xxx" QMP command.
> 
> cpu-add's "id" argument is a CPU number in a range [0..max-cpus)
> 
> Example QMP command:
>  -> { "execute": "cpu-add", "arguments": { "id": 2 } }
>  <- { "return": {} }
> 
> Signed-off-by: Igor Mammedov <imammedo@redhat.com>
> Acked-by: Luiz Capitulino <lcapitulino@redhat.com>
> Reviewed-by: Eric Blake <eblake@redhat.com>

The only way to find out if CPU hotplug is really available on a given
machine-type is by actually trying to run cpu-add, right? Is this
sufficient for libvirt requirements?


> ---
> v7:
>   * added "Since 1.5" to cpu-add qapi schema definition
> v6:
>   * added valid values description to qapi schema
>   * split out cpu_hot_add hooks introduction into separate patch
>   * split out implementation of cpu_hot_add for target-i386
> v5:
>   * accept id=[0..max_cpus) range in cpu-add command
> v4:
>   * merge "qmp: add cpu-add qmp command" & "target-i386: implement CPU hot-add" patches
>   * move notifier call to CPUCLass.realize()
>   * add hook cpu_hot_add to QEMUMachine
>   * make QEMUMachineInitArgs global and keep default cpu_model there
> 
> v3:
>   * it appears that 'online/offline' in cpu-set are confusing people
>     with what command actually does and users might have to distinguish
>     if 'offline' is not implemented by parsing error message. To simplify
>     things replace cpu-set with cpu-add command to show more clear what
>     command does and just add cpu-del when CPU remove is implemented.
> 
> v2:
>   * s/cpu_set/cpu-set/
>   * qmp doc style fix
>   * use bool type instead of opencodding online/offline string
>      suggested-by: Eric Blake <eblake@redhat.com>
> ---
>  qapi-schema.json | 13 +++++++++++++
>  qmp-commands.hx  | 23 +++++++++++++++++++++++
>  qmp.c            | 10 ++++++++++
>  3 files changed, 46 insertions(+)
> 
> diff --git a/qapi-schema.json b/qapi-schema.json
> index 5b0fb3b..6f58b0f 100644
> --- a/qapi-schema.json
> +++ b/qapi-schema.json
> @@ -1387,6 +1387,19 @@
>  { 'command': 'cpu', 'data': {'index': 'int'} }
>  
>  ##
> +# @cpu-add
> +#
> +# Adds CPU with specified ID
> +#
> +# @id: ID of CPU to be created, valid values [0..max_cpus)
> +#
> +# Returns: Nothing on success
> +#
> +# Since 1.5
> +##
> +{ 'command': 'cpu-add', 'data': {'id': 'int'} }
> +
> +##
>  # @memsave:
>  #
>  # Save a portion of guest memory to a file.
> diff --git a/qmp-commands.hx b/qmp-commands.hx
> index 0e89132..ed99eb8 100644
> --- a/qmp-commands.hx
> +++ b/qmp-commands.hx
> @@ -385,6 +385,29 @@ Note: CPUs' indexes are obtained with the 'query-cpus' command.
>  EQMP
>  
>      {
> +        .name       = "cpu-add",
> +        .args_type  = "id:i",
> +        .mhandler.cmd_new = qmp_marshal_input_cpu_add,
> +    },
> +
> +SQMP
> +cpu-add
> +-------
> +
> +Adds virtual cpu
> +
> +Arguments:
> +
> +- "id": cpu id (json-int)
> +
> +Example:
> +
> +-> { "execute": "cpu-add", "arguments": { "id": 2 } }
> +<- { "return": {} }
> +
> +EQMP
> +
> +    {
>          .name       = "memsave",
>          .args_type  = "val:l,size:i,filename:s,cpu:i?",
>          .mhandler.cmd_new = qmp_marshal_input_memsave,
> diff --git a/qmp.c b/qmp.c
> index ed6c7ef..dd34be6 100644
> --- a/qmp.c
> +++ b/qmp.c
> @@ -24,6 +24,7 @@
>  #include "hw/qdev.h"
>  #include "sysemu/blockdev.h"
>  #include "qom/qom-qobject.h"
> +#include "hw/boards.h"
>  
>  NameInfo *qmp_query_name(Error **errp)
>  {
> @@ -108,6 +109,15 @@ void qmp_cpu(int64_t index, Error **errp)
>      /* Just do nothing */
>  }
>  
> +void qmp_cpu_add(int64_t id, Error **errp)
> +{
> +    if (current_machine->hot_add_cpu) {
> +        current_machine->hot_add_cpu(id, errp);
> +    } else {
> +        error_setg(errp, "Not supported");
> +    }
> +}
> +
>  #ifndef CONFIG_VNC
>  /* If VNC support is enabled, the "true" query-vnc command is
>     defined in the VNC subsystem */
> -- 
> 1.8.2.1
> 

-- 
Eduardo

Re: [Qemu-devel] [libvirt] [PATCH 2/4] QMP: add cpu-add command

[Peter Krempa]

On 04/30/13 15:46, Eduardo Habkost wrote:
> (CCing libvir-list)
>
> On Tue, Apr 30, 2013 at 08:34:01AM +0200, Igor Mammedov wrote:
>> Adds "cpu-add id=xxx" QMP command.
>>
>> cpu-add's "id" argument is a CPU number in a range [0..max-cpus)
>>
>> Example QMP command:
>>   -> { "execute": "cpu-add", "arguments": { "id": 2 } }
>>   <- { "return": {} }
>>
>> Signed-off-by: Igor Mammedov <imammedo@redhat.com>
>> Acked-by: Luiz Capitulino <lcapitulino@redhat.com>
>> Reviewed-by: Eric Blake <eblake@redhat.com>
>
> The only way to find out if CPU hotplug is really available on a given
> machine-type is by actually trying to run cpu-add, right? Is this
> sufficient for libvirt requirements?
>
>


As long as the command fails when it's not supported it's okay.

(cpu_set HMP command does not fail when offlining a cpu even if it isn't 
supported and that's real pain to use)

Peter

Re: [Qemu-devel] [PATCH 2/4] QMP: add cpu-add command

[Igor Mammedov]

On Tue, 30 Apr 2013 10:46:20 -0300
Eduardo Habkost <ehabkost@redhat.com> wrote:

> (CCing libvir-list)
> 
> On Tue, Apr 30, 2013 at 08:34:01AM +0200, Igor Mammedov wrote:
> > Adds "cpu-add id=xxx" QMP command.
> > 
> > cpu-add's "id" argument is a CPU number in a range [0..max-cpus)
> > 
> > Example QMP command:
> >  -> { "execute": "cpu-add", "arguments": { "id": 2 } }
> >  <- { "return": {} }
> > 
> > Signed-off-by: Igor Mammedov <imammedo@redhat.com>
> > Acked-by: Luiz Capitulino <lcapitulino@redhat.com>
> > Reviewed-by: Eric Blake <eblake@redhat.com>
> 
> The only way to find out if CPU hotplug is really available on a given
> machine-type is by actually trying to run cpu-add, right? Is this
> sufficient for libvirt requirements?
yes, for now it is the only way.it was acked from their side.

> 
> 
> > ---
> > v7:
> >   * added "Since 1.5" to cpu-add qapi schema definition
> > v6:
> >   * added valid values description to qapi schema
> >   * split out cpu_hot_add hooks introduction into separate patch
> >   * split out implementation of cpu_hot_add for target-i386
> > v5:
> >   * accept id=[0..max_cpus) range in cpu-add command
> > v4:
> >   * merge "qmp: add cpu-add qmp command" & "target-i386: implement CPU hot-add" patches
> >   * move notifier call to CPUCLass.realize()
> >   * add hook cpu_hot_add to QEMUMachine
> >   * make QEMUMachineInitArgs global and keep default cpu_model there
> > 
> > v3:
> >   * it appears that 'online/offline' in cpu-set are confusing people
> >     with what command actually does and users might have to distinguish
> >     if 'offline' is not implemented by parsing error message. To simplify
> >     things replace cpu-set with cpu-add command to show more clear what
> >     command does and just add cpu-del when CPU remove is implemented.
> > 
> > v2:
> >   * s/cpu_set/cpu-set/
> >   * qmp doc style fix
> >   * use bool type instead of opencodding online/offline string
> >      suggested-by: Eric Blake <eblake@redhat.com>
> > ---
> >  qapi-schema.json | 13 +++++++++++++
> >  qmp-commands.hx  | 23 +++++++++++++++++++++++
> >  qmp.c            | 10 ++++++++++
> >  3 files changed, 46 insertions(+)
> > 
> > diff --git a/qapi-schema.json b/qapi-schema.json
> > index 5b0fb3b..6f58b0f 100644
> > --- a/qapi-schema.json
> > +++ b/qapi-schema.json
> > @@ -1387,6 +1387,19 @@
> >  { 'command': 'cpu', 'data': {'index': 'int'} }
> >  
> >  ##
> > +# @cpu-add
> > +#
> > +# Adds CPU with specified ID
> > +#
> > +# @id: ID of CPU to be created, valid values [0..max_cpus)
> > +#
> > +# Returns: Nothing on success
> > +#
> > +# Since 1.5
> > +##
> > +{ 'command': 'cpu-add', 'data': {'id': 'int'} }
> > +
> > +##
> >  # @memsave:
> >  #
> >  # Save a portion of guest memory to a file.
> > diff --git a/qmp-commands.hx b/qmp-commands.hx
> > index 0e89132..ed99eb8 100644
> > --- a/qmp-commands.hx
> > +++ b/qmp-commands.hx
> > @@ -385,6 +385,29 @@ Note: CPUs' indexes are obtained with the 'query-cpus' command.
> >  EQMP
> >  
> >      {
> > +        .name       = "cpu-add",
> > +        .args_type  = "id:i",
> > +        .mhandler.cmd_new = qmp_marshal_input_cpu_add,
> > +    },
> > +
> > +SQMP
> > +cpu-add
> > +-------
> > +
> > +Adds virtual cpu
> > +
> > +Arguments:
> > +
> > +- "id": cpu id (json-int)
> > +
> > +Example:
> > +
> > +-> { "execute": "cpu-add", "arguments": { "id": 2 } }
> > +<- { "return": {} }
> > +
> > +EQMP
> > +
> > +    {
> >          .name       = "memsave",
> >          .args_type  = "val:l,size:i,filename:s,cpu:i?",
> >          .mhandler.cmd_new = qmp_marshal_input_memsave,
> > diff --git a/qmp.c b/qmp.c
> > index ed6c7ef..dd34be6 100644
> > --- a/qmp.c
> > +++ b/qmp.c
> > @@ -24,6 +24,7 @@
> >  #include "hw/qdev.h"
> >  #include "sysemu/blockdev.h"
> >  #include "qom/qom-qobject.h"
> > +#include "hw/boards.h"
> >  
> >  NameInfo *qmp_query_name(Error **errp)
> >  {
> > @@ -108,6 +109,15 @@ void qmp_cpu(int64_t index, Error **errp)
> >      /* Just do nothing */
> >  }
> >  
> > +void qmp_cpu_add(int64_t id, Error **errp)
> > +{
> > +    if (current_machine->hot_add_cpu) {
> > +        current_machine->hot_add_cpu(id, errp);
> > +    } else {
> > +        error_setg(errp, "Not supported");
> > +    }
> > +}
> > +
> >  #ifndef CONFIG_VNC
> >  /* If VNC support is enabled, the "true" query-vnc command is
> >     defined in the VNC subsystem */
> > -- 
> > 1.8.2.1
> > 
>