Re: [Qemu-devel] [RFC PATCH V6 08/18] cpu: remove exit_request global.

[Paolo Bonzini <pbonzini@redhat.com>]

On 26/06/2015 16:47, fred.konrad@greensocs.com wrote:
> From: KONRAD Frederic <fred.konrad@greensocs.com>
> 
> This removes exit_request global and adds a variable in CPUState for this.
> Only the flag for the first cpu is used for the moment as we are still with one
> TCG thread.

I think this should also be added to CPUThread.

Paolo

> Signed-off-by: KONRAD Frederic <fred.konrad@greensocs.com>
> ---
>  cpu-exec.c | 15 ---------------
>  cpus.c     | 17 ++++++++++++++---
>  2 files changed, 14 insertions(+), 18 deletions(-)
> 
> diff --git a/cpu-exec.c b/cpu-exec.c
> index 5d9b518..0644383 100644
> --- a/cpu-exec.c
> +++ b/cpu-exec.c
> @@ -364,8 +364,6 @@ static void cpu_handle_debug_exception(CPUArchState *env)
>  
>  /* main execution loop */
>  
> -volatile sig_atomic_t exit_request;
> -
>  int cpu_exec(CPUArchState *env)
>  {
>      CPUState *cpu = ENV_GET_CPU(env);
> @@ -394,20 +392,8 @@ int cpu_exec(CPUArchState *env)
>  
>      current_cpu = cpu;
>  
> -    /* As long as current_cpu is null, up to the assignment just above,
> -     * requests by other threads to exit the execution loop are expected to
> -     * be issued using the exit_request global. We must make sure that our
> -     * evaluation of the global value is performed past the current_cpu
> -     * value transition point, which requires a memory barrier as well as
> -     * an instruction scheduling constraint on modern architectures.  */
> -    smp_mb();
> -
>      rcu_read_lock();
>  
> -    if (unlikely(exit_request)) {
> -        cpu->exit_request = 1;
> -    }
> -
>      cc->cpu_exec_enter(cpu);
>  
>      /* Calculate difference between guest clock and host clock.
> @@ -496,7 +482,6 @@ int cpu_exec(CPUArchState *env)
>                      }
>                  }
>                  if (unlikely(cpu->exit_request)) {
> -                    cpu->exit_request = 0;
>                      cpu->exception_index = EXCP_INTERRUPT;
>                      cpu_loop_exit(cpu);
>                  }
> diff --git a/cpus.c b/cpus.c
> index 23c316c..2541c56 100644
> --- a/cpus.c
> +++ b/cpus.c
> @@ -137,6 +137,8 @@ typedef struct TimersState {
>  } TimersState;
>  
>  static TimersState timers_state;
> +/* CPU associated to this thread. */
> +static __thread CPUState *tcg_thread_cpu;
>  
>  int64_t cpu_get_icount_raw(void)
>  {
> @@ -661,12 +663,18 @@ static void cpu_handle_guest_debug(CPUState *cpu)
>      cpu->stopped = true;
>  }
>  
> +/**
> + * cpu_signal
> + * Signal handler when using TCG.
> + */
>  static void cpu_signal(int sig)
>  {
>      if (current_cpu) {
>          cpu_exit(current_cpu);
>      }
> -    exit_request = 1;
> +
> +    /* FIXME: We might want to check if the cpu is running? */
> +    tcg_thread_cpu->exit_request = true;
>  }
>  
>  #ifdef CONFIG_LINUX
> @@ -1031,6 +1039,7 @@ static void *qemu_tcg_cpu_thread_fn(void *arg)
>  {
>      CPUState *cpu = arg;
>  
> +    tcg_thread_cpu = cpu;
>      qemu_tcg_init_cpu_signals();
>      qemu_thread_get_self(cpu->thread);
>  
> @@ -1393,7 +1402,8 @@ static void tcg_exec_all(void)
>      if (next_cpu == NULL) {
>          next_cpu = first_cpu;
>      }
> -    for (; next_cpu != NULL && !exit_request; next_cpu = CPU_NEXT(next_cpu)) {
> +    for (; next_cpu != NULL && !first_cpu->exit_request;
> +           next_cpu = CPU_NEXT(next_cpu)) {
>          CPUState *cpu = next_cpu;
>          CPUArchState *env = cpu->env_ptr;
>  
> @@ -1410,7 +1420,8 @@ static void tcg_exec_all(void)
>              break;
>          }
>      }
> -    exit_request = 0;
> +
> +    first_cpu->exit_request = 0;
>  }
>  
>  void list_cpus(FILE *f, fprintf_function cpu_fprintf, const char *optarg)
>