Re: [PATCH 11/18] accel/tcg: create a thread-kick function for TCG

[Igor Mammedov <imammedo@redhat.com>]

On Fri, 29 Aug 2025 17:31:08 +0200
Paolo Bonzini <pbonzini@redhat.com> wrote:

> Round-robin TCG is calling into cpu_exit() directly.  In preparation
> for making cpu_exit() usable from all accelerators, define a generic
> thread-kick function for TCG which is used directly in the multi-threaded
> case, and through CPU_FOREACH in the round-robin case.
> 
> Use it also for user-mode emulation, and take the occasion to move
> the implementation to accel/tcg/user-exec.c.
> 
> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

Reviewed-by: Igor Mammedov <imammedo@redhat.com>

> ---
>  docs/devel/tcg-icount.rst       | 2 +-
>  accel/tcg/tcg-accel-ops-mttcg.h | 3 ---
>  accel/tcg/tcg-accel-ops.h       | 1 +
>  accel/tcg/cpu-exec.c            | 6 ++++++
>  accel/tcg/tcg-accel-ops-mttcg.c | 5 -----
>  accel/tcg/tcg-accel-ops-rr.c    | 2 +-
>  accel/tcg/tcg-accel-ops.c       | 2 +-
>  accel/tcg/user-exec.c           | 6 ++++++
>  bsd-user/main.c                 | 5 -----
>  linux-user/main.c               | 5 -----
>  10 files changed, 16 insertions(+), 21 deletions(-)
> 
> diff --git a/docs/devel/tcg-icount.rst b/docs/devel/tcg-icount.rst
> index 7df883446a7..a1dcd79e0fd 100644
> --- a/docs/devel/tcg-icount.rst
> +++ b/docs/devel/tcg-icount.rst
> @@ -37,7 +37,7 @@ translator starts by allocating a budget of instructions to be
>  executed. The budget of instructions is limited by how long it will be
>  until the next timer will expire. We store this budget as part of a
>  vCPU icount_decr field which shared with the machinery for handling
> -cpu_exit(). The whole field is checked at the start of every
> +qemu_cpu_kick(). The whole field is checked at the start of every
>  translated block and will cause a return to the outer loop to deal
>  with whatever caused the exit.
>  
> diff --git a/accel/tcg/tcg-accel-ops-mttcg.h b/accel/tcg/tcg-accel-ops-mttcg.h
> index 8ffa7a9a9fe..5c145cc8595 100644
> --- a/accel/tcg/tcg-accel-ops-mttcg.h
> +++ b/accel/tcg/tcg-accel-ops-mttcg.h
> @@ -10,9 +10,6 @@
>  #ifndef TCG_ACCEL_OPS_MTTCG_H
>  #define TCG_ACCEL_OPS_MTTCG_H
>  
> -/* kick MTTCG vCPU thread */
> -void mttcg_kick_vcpu_thread(CPUState *cpu);
> -
>  /* start an mttcg vCPU thread */
>  void mttcg_start_vcpu_thread(CPUState *cpu);
>  
> diff --git a/accel/tcg/tcg-accel-ops.h b/accel/tcg/tcg-accel-ops.h
> index 6feeb3f3e9b..aecce605d7b 100644
> --- a/accel/tcg/tcg-accel-ops.h
> +++ b/accel/tcg/tcg-accel-ops.h
> @@ -18,5 +18,6 @@ void tcg_cpu_destroy(CPUState *cpu);
>  int tcg_cpu_exec(CPUState *cpu);
>  void tcg_handle_interrupt(CPUState *cpu, int mask);
>  void tcg_cpu_init_cflags(CPUState *cpu, bool parallel);
> +void tcg_kick_vcpu_thread(CPUState *cpu);
>  
>  #endif /* TCG_ACCEL_OPS_H */
> diff --git a/accel/tcg/cpu-exec.c b/accel/tcg/cpu-exec.c
> index f838535d111..9241bcadb5f 100644
> --- a/accel/tcg/cpu-exec.c
> +++ b/accel/tcg/cpu-exec.c
> @@ -40,6 +40,7 @@
>  #include "exec/replay-core.h"
>  #include "system/tcg.h"
>  #include "exec/helper-proto-common.h"
> +#include "tcg-accel-ops.h"
>  #include "tb-jmp-cache.h"
>  #include "tb-hash.h"
>  #include "tb-context.h"
> @@ -748,6 +749,11 @@ static inline bool cpu_handle_exception(CPUState *cpu, int *ret)
>      return false;
>  }
>  
> +void tcg_kick_vcpu_thread(CPUState *cpu)
> +{
> +    cpu_exit(cpu);
> +}
> +
>  static inline bool icount_exit_request(CPUState *cpu)
>  {
>      if (!icount_enabled()) {
> diff --git a/accel/tcg/tcg-accel-ops-mttcg.c b/accel/tcg/tcg-accel-ops-mttcg.c
> index b12b7a36b5d..1148ebcaae5 100644
> --- a/accel/tcg/tcg-accel-ops-mttcg.c
> +++ b/accel/tcg/tcg-accel-ops-mttcg.c
> @@ -123,11 +123,6 @@ static void *mttcg_cpu_thread_fn(void *arg)
>      return NULL;
>  }
>  
> -void mttcg_kick_vcpu_thread(CPUState *cpu)
> -{
> -    cpu_exit(cpu);
> -}
> -
>  void mttcg_start_vcpu_thread(CPUState *cpu)
>  {
>      char thread_name[VCPU_THREAD_NAME_SIZE];
> diff --git a/accel/tcg/tcg-accel-ops-rr.c b/accel/tcg/tcg-accel-ops-rr.c
> index c2468d15d4f..610292d3bac 100644
> --- a/accel/tcg/tcg-accel-ops-rr.c
> +++ b/accel/tcg/tcg-accel-ops-rr.c
> @@ -43,7 +43,7 @@ void rr_kick_vcpu_thread(CPUState *unused)
>      CPUState *cpu;
>  
>      CPU_FOREACH(cpu) {
> -        cpu_exit(cpu);
> +        tcg_kick_vcpu_thread(cpu);
>      };
>  }
>  
> diff --git a/accel/tcg/tcg-accel-ops.c b/accel/tcg/tcg-accel-ops.c
> index 9c37266c1e0..1f662a9c745 100644
> --- a/accel/tcg/tcg-accel-ops.c
> +++ b/accel/tcg/tcg-accel-ops.c
> @@ -206,7 +206,7 @@ static void tcg_accel_ops_init(AccelClass *ac)
>  
>      if (qemu_tcg_mttcg_enabled()) {
>          ops->create_vcpu_thread = mttcg_start_vcpu_thread;
> -        ops->kick_vcpu_thread = mttcg_kick_vcpu_thread;
> +        ops->kick_vcpu_thread = tcg_kick_vcpu_thread;
>          ops->handle_interrupt = tcg_handle_interrupt;
>      } else {
>          ops->create_vcpu_thread = rr_start_vcpu_thread;
> diff --git a/accel/tcg/user-exec.c b/accel/tcg/user-exec.c
> index 66c25fba7dd..3c072fd868f 100644
> --- a/accel/tcg/user-exec.c
> +++ b/accel/tcg/user-exec.c
> @@ -38,6 +38,7 @@
>  #include "qemu/int128.h"
>  #include "trace.h"
>  #include "tcg/tcg-ldst.h"
> +#include "tcg-accel-ops.h"
>  #include "backend-ldst.h"
>  #include "internal-common.h"
>  #include "tb-internal.h"
> @@ -46,6 +47,11 @@ __thread uintptr_t helper_retaddr;
>  
>  //#define DEBUG_SIGNAL
>  
> +void qemu_cpu_kick(CPUState *cpu)
> +{
> +    tcg_kick_vcpu_thread(cpu);
> +}
> +
>  /*
>   * Adjust the pc to pass to cpu_restore_state; return the memop type.
>   */
> diff --git a/bsd-user/main.c b/bsd-user/main.c
> index 7e5d4bbce09..fc33e4d4880 100644
> --- a/bsd-user/main.c
> +++ b/bsd-user/main.c
> @@ -214,11 +214,6 @@ bool qemu_cpu_is_self(CPUState *cpu)
>      return thread_cpu == cpu;
>  }
>  
> -void qemu_cpu_kick(CPUState *cpu)
> -{
> -    cpu_exit(cpu);
> -}
> -
>  /* Assumes contents are already zeroed.  */
>  static void init_task_state(TaskState *ts)
>  {
> diff --git a/linux-user/main.c b/linux-user/main.c
> index 6edeeecef38..2ba073eb830 100644
> --- a/linux-user/main.c
> +++ b/linux-user/main.c
> @@ -189,11 +189,6 @@ bool qemu_cpu_is_self(CPUState *cpu)
>      return thread_cpu == cpu;
>  }
>  
> -void qemu_cpu_kick(CPUState *cpu)
> -{
> -    cpu_exit(cpu);
> -}
> -
>  void task_settid(TaskState *ts)
>  {
>      if (ts->ts_tid == 0) {