Re: [Qemu-devel] [RFC v0 PATCH] cpus: Convert cpu_index into a bitmap

[Alexander Graf <agraf@suse.de>]

On 13.03.15 12:56, Bharata B Rao wrote:
> From: Bharata B Rao <bharata.rao@gmail.com>
> 
> Currently CPUState.cpu_index is monotonically increasing and a newly
> created CPU always gets the next higher index. The next available
> index is calculated by counting the existing number of CPUs. This is
> fine as long as we only add CPUs, but there are architectures which
> are starting to support CPU removal too. For an architecture like PowerPC
> which derives its CPU identifier (device tree ID) from cpu_index, the
> existing logic of generating cpu_index values causes problems.
> 
> With the currently proposed method of handling vCPU removal by parking
> the vCPU fd in QEMU
> (Ref: http://lists.gnu.org/archive/html/qemu-devel/2015-02/msg02604.html),
> generating cpu_index this way will not work for PowerPC.
> 
> This patch changes the way cpu_index is handed out by maintaining
> a bit map of the CPUs that tracks both addition and removal of CPUs.
> 
> I am not sure if this is the right and an acceptable approach. The
> alternative is to do something similar for PowerPC alone and not
> depend on cpu_index.
> 
> I have tested this with out-of-the-tree patches for CPU hot plug and
> removal on x86 and sPAPR PowerPC.
> 
> Signed-off-by: Bharata B Rao <bharata@linux.vnet.ibm.com>
> ---
>  exec.c                      | 39 +++++++++++++++++++++++++++++----------
>  include/exec/exec-all.h     |  1 +
>  target-alpha/cpu.c          |  6 ++++++
>  target-arm/cpu.c            |  1 +
>  target-cris/cpu.c           |  6 ++++++
>  target-i386/cpu.c           |  6 ++++++
>  target-lm32/cpu.c           |  6 ++++++
>  target-m68k/cpu.c           |  6 ++++++
>  target-microblaze/cpu.c     |  6 ++++++
>  target-mips/cpu.c           |  6 ++++++
>  target-moxie/cpu.c          |  6 ++++++
>  target-openrisc/cpu.c       |  6 ++++++
>  target-ppc/translate_init.c |  6 ++++++
>  target-s390x/cpu.c          |  1 +
>  target-sh4/cpu.c            |  6 ++++++
>  target-sparc/cpu.c          |  1 +
>  target-tricore/cpu.c        |  5 +++++
>  target-unicore32/cpu.c      |  6 ++++++
>  target-xtensa/cpu.c         |  6 ++++++
>  19 files changed, 116 insertions(+), 10 deletions(-)
> 
> diff --git a/exec.c b/exec.c
> index e97071a..7760f2d 100644
> --- a/exec.c
> +++ b/exec.c
> @@ -530,21 +530,40 @@ void tcg_cpu_address_space_init(CPUState *cpu, AddressSpace *as)
>  }
>  #endif
>  
> +static DECLARE_BITMAP(cpu_index_map, MAX_CPUMASK_BITS);
> +
> +#ifdef CONFIG_USER_ONLY
> +int max_cpus = 1; /* TODO: Check if this is correct ? */
> +#endif
> +
> +static int cpu_get_free_index(void)
> +{
> +    int cpu = find_first_zero_bit(cpu_index_map, max_cpus);
> +
> +    if (cpu == max_cpus) {
> +        fprintf(stderr, "WARNING: qemu: Trying to use more "
> +                        "CPUs than allowed max of %d\n", max_cpus);
> +        return max_cpus;
> +    } else {
> +        bitmap_set(cpu_index_map, cpu, 1);
> +        return cpu;
> +    }
> +}
> +
> +void cpu_exec_exit(CPUState *cpu)
> +{
> +    bitmap_clear(cpu_index_map, cpu->cpu_index, 1);
> +}
> +
>  void cpu_exec_init(CPUArchState *env)
>  {
>      CPUState *cpu = ENV_GET_CPU(env);
>      CPUClass *cc = CPU_GET_CLASS(cpu);
> -    CPUState *some_cpu;
> -    int cpu_index;
>  
>  #if defined(CONFIG_USER_ONLY)
>      cpu_list_lock();
>  #endif
> -    cpu_index = 0;
> -    CPU_FOREACH(some_cpu) {
> -        cpu_index++;
> -    }
> -    cpu->cpu_index = cpu_index;
> +    cpu->cpu_index = cpu_get_free_index();
>      cpu->numa_node = 0;
>      QTAILQ_INIT(&cpu->breakpoints);
>      QTAILQ_INIT(&cpu->watchpoints);
> @@ -558,16 +577,16 @@ void cpu_exec_init(CPUArchState *env)
>      cpu_list_unlock();
>  #endif
>      if (qdev_get_vmsd(DEVICE(cpu)) == NULL) {
> -        vmstate_register(NULL, cpu_index, &vmstate_cpu_common, cpu);
> +        vmstate_register(NULL, cpu->cpu_index, &vmstate_cpu_common, cpu);
>      }
>  #if defined(CPU_SAVE_VERSION) && !defined(CONFIG_USER_ONLY)
> -    register_savevm(NULL, "cpu", cpu_index, CPU_SAVE_VERSION,
> +    register_savevm(NULL, "cpu", cpu->cpu_index, CPU_SAVE_VERSION,
>                      cpu_save, cpu_load, env);
>      assert(cc->vmsd == NULL);
>      assert(qdev_get_vmsd(DEVICE(cpu)) == NULL);
>  #endif
>      if (cc->vmsd != NULL) {
> -        vmstate_register(NULL, cpu_index, cc->vmsd, cpu);
> +        vmstate_register(NULL, cpu->cpu_index, cc->vmsd, cpu);
>      }
>  }
>  
> diff --git a/include/exec/exec-all.h b/include/exec/exec-all.h
> index 8eb0db3..95fbba0 100644
> --- a/include/exec/exec-all.h
> +++ b/include/exec/exec-all.h
> @@ -89,6 +89,7 @@ TranslationBlock *tb_gen_code(CPUState *cpu,
>                                target_ulong pc, target_ulong cs_base, int flags,
>                                int cflags);
>  void cpu_exec_init(CPUArchState *env);
> +void cpu_exec_exit(CPUState *cpu);
>  void QEMU_NORETURN cpu_loop_exit(CPUState *cpu);
>  int page_unprotect(target_ulong address, uintptr_t pc, void *puc);
>  void tb_invalidate_phys_page_range(tb_page_addr_t start, tb_page_addr_t end,
> diff --git a/target-alpha/cpu.c b/target-alpha/cpu.c
> index a98b7d8..7c57165 100644
> --- a/target-alpha/cpu.c
> +++ b/target-alpha/cpu.c
> @@ -250,6 +250,11 @@ static const TypeInfo ev68_cpu_type_info = {
>      .parent = TYPE("ev67"),
>  };
>  
> +static void alpha_cpu_finalize(Object *obj)
> +{
> +    cpu_exec_exit(CPU(obj));
> +}
> +
>  static void alpha_cpu_initfn(Object *obj)
>  {
>      CPUState *cs = CPU(obj);
> @@ -305,6 +310,7 @@ static const TypeInfo alpha_cpu_type_info = {
>      .parent = TYPE_CPU,
>      .instance_size = sizeof(AlphaCPU),
>      .instance_init = alpha_cpu_initfn,
> +    .instance_finalize = alpha_cpu_finalize,

Would it be possible to put this into TYPE_CPU->instance_finalize instead?


Alex