On Tue, 5 Jul 2016 10:12:49 +0530
Bharata B Rao <bhar...@linux.vnet.ibm.com> wrote:
> Introduce CPUState.prefer_arch_id_over_cpu_index and
> MachineClass.prefer_arch_id_over_cpu_index that allow target
> machines to optionally switch to using arch_id instead of cpu_index
> as instance_id in vmstate_register(). This will help allow successful
> migration in cases where holes are introduced in cpu_index range
> after CPU hot removals.
>
> Whether to use arch_id or cpu_index is based on machine type version
> and hence added MachineClass.prefer_arch_id_over_cpu_index. However the
> enforcement is via and during CPU creation and hence added
> CPUState.prefer_arch_id_over_cpu_index. So it becomes a two step
> process for the target to enable the use of arch_id:
>
> 1. Set MachineClass.prefer_arch_id_over_cpu_index.
> 2. Ensure CPUState.prefer_arch_id_over_cpu_index is set for all CPUs
> based on 1. above.
>
> Suggested-by: Igor Mammedov <imamm...@redhat.com>
> Signed-off-by: Bharata B Rao <bhar...@linux.vnet.ibm.com>
> ---
> exec.c | 10 ++++++++--
> include/hw/boards.h | 1 +
> include/qom/cpu.h | 4 ++++
> 3 files changed, 13 insertions(+), 2 deletions(-)
>
> diff --git a/exec.c b/exec.c
> index 8ce8e90..7cc1d06 100644
> --- a/exec.c
> +++ b/exec.c
> @@ -616,15 +616,21 @@ static void cpu_release_index(CPUState *cpu)
> bitmap_clear(cpu_index_map, cpu->cpu_index, 1);
> }
>
> +/*
> + * TODO: cpu_index and instance_id are of type int while .get_arch_id()is
> + * of type int64_t. What is the consequence of changing instance_id to
> int64_t ?
> + */
The current migration code assumes instance_id is a 32-bit word:
migration/savevm.c: qemu_put_be32(f, se->instance_id);
> static void cpu_vmstate_register(CPUState *cpu)
> {
> CPUClass *cc = CPU_GET_CLASS(cpu);
> + int instance_id = cpu->prefer_arch_id_over_cpu_index ?
> + cc->get_arch_id(cpu) : cpu->cpu_index;
>
> if (qdev_get_vmsd(DEVICE(cpu)) == NULL) {
> - vmstate_register(NULL, cpu->cpu_index, &vmstate_cpu_common, cpu);
> + vmstate_register(NULL, instance_id, &vmstate_cpu_common, cpu);
> }
> if (cc->vmsd != NULL) {
> - vmstate_register(NULL, cpu->cpu_index, cc->vmsd, cpu);
> + vmstate_register(NULL, instance_id, cc->vmsd, cpu);
> }
> }
>
> diff --git a/include/hw/boards.h b/include/hw/boards.h
> index 3ed6155..decabba 100644
> --- a/include/hw/boards.h
> +++ b/include/hw/boards.h
> @@ -123,6 +123,7 @@ struct MachineClass {
> ram_addr_t default_ram_size;
> bool option_rom_has_mr;
> bool rom_file_has_mr;
> + bool prefer_arch_id_over_cpu_index;
>
> HotplugHandler *(*get_hotplug_handler)(MachineState *machine,
> DeviceState *dev);
> diff --git a/include/qom/cpu.h b/include/qom/cpu.h
> index 32f3af3..1f1706e 100644
> --- a/include/qom/cpu.h
> +++ b/include/qom/cpu.h
> @@ -273,6 +273,9 @@ struct qemu_work_item {
> * @kvm_fd: vCPU file descriptor for KVM.
> * @work_mutex: Lock to prevent multiple access to queued_work_*.
> * @queued_work_first: First asynchronous work pending.
> + * @prefer_arch_id_over_cpu_index: Set to enforce the use of
> + * CPUClass.get_arch_id() over cpu_index during vmstate registration
> + * and any other uses by target machine where arch_id is preferred.
> *
> * State of one CPU core or thread.
> */
> @@ -360,6 +363,7 @@ struct CPUState {
> (absolute value) offset as small as possible. This reduces code
> size, especially for hosts without large memory offsets. */
> uint32_t tcg_exit_req;
> + bool prefer_arch_id_over_cpu_index;
> };
>
> QTAILQ_HEAD(CPUTailQ, CPUState);
