Re: [Qemu-devel] [PATCH] cpus: unify qemu_*_wait_io_event

["Alex Bennée" <alex.bennee@linaro.org>]

Paolo Bonzini <pbonzini@redhat.com> writes:

> Except for round-robin TCG, every other accelerator is using more or
> less the same code around qemu_wait_io_event_common.  The exception
> is HAX, which also has to eat the dummy APC that is queued by
> qemu_cpu_kick_thread.
>
> We can add the SleepEx call to qemu_wait_io_event under "if
> (!tcg_enabled())", since that is the condition that is used in
> qemu_cpu_kick_thread, and unify the function for KVM, HAX, HVF and
> multi-threaded TCG.  Single-threaded TCG code can also be simplified
> since it is only used in the round-robin, sleep-if-all-CPUs-idle case.
>
> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

I had trouble applying this patch but the change seems sane to me

Acked-by: Alex Bennée <alex.bennee@linaro.org>

> ---
>  cpus.c | 49 +++++++++++++++++--------------------------------
>  1 file changed, 17 insertions(+), 32 deletions(-)
>
> diff --git a/cpus.c b/cpus.c
> index 440b9291f5..3b6c9879ec 100644
> --- a/cpus.c
> +++ b/cpus.c
> @@ -911,7 +911,8 @@ static void kick_tcg_thread(void *opaque)
>
>  static void start_tcg_kick_timer(void)
>  {
> -    if (!mttcg_enabled && !tcg_kick_vcpu_timer && CPU_NEXT(first_cpu)) {
> +    assert(!mttcg_enabled);
> +    if (!tcg_kick_vcpu_timer && CPU_NEXT(first_cpu)) {
>          tcg_kick_vcpu_timer = timer_new_ns(QEMU_CLOCK_VIRTUAL,
>                                             kick_tcg_thread, NULL);
>          timer_mod(tcg_kick_vcpu_timer, qemu_tcg_next_kick());
> @@ -920,6 +921,7 @@ static void start_tcg_kick_timer(void)
>
>  static void stop_tcg_kick_timer(void)
>  {
> +    assert(!mttcg_enabled);
>      if (tcg_kick_vcpu_timer) {
>          timer_del(tcg_kick_vcpu_timer);
>          tcg_kick_vcpu_timer = NULL;
> @@ -1154,18 +1156,9 @@ static void qemu_wait_io_event_common(CPUState *cpu)
>      process_queued_cpu_work(cpu);
>  }
>
> -static bool qemu_tcg_should_sleep(CPUState *cpu)
> +static void qemu_tcg_rr_wait_io_event(CPUState *cpu)
>  {
> -    if (mttcg_enabled) {
> -        return cpu_thread_is_idle(cpu);
> -    } else {
> -        return all_cpu_threads_idle();
> -    }
> -}
> -
> -static void qemu_tcg_wait_io_event(CPUState *cpu)
> -{
> -    while (qemu_tcg_should_sleep(cpu)) {
> +    while (all_cpu_threads_idle()) {
>          stop_tcg_kick_timer();
>          qemu_cond_wait(cpu->halt_cond, &qemu_global_mutex);
>      }
> @@ -1175,20 +1168,18 @@ static void qemu_tcg_wait_io_event(CPUState *cpu)
>      qemu_wait_io_event_common(cpu);
>  }
>
> -static void qemu_kvm_wait_io_event(CPUState *cpu)
> +static void qemu_wait_io_event(CPUState *cpu)
>  {
>      while (cpu_thread_is_idle(cpu)) {
>          qemu_cond_wait(cpu->halt_cond, &qemu_global_mutex);
>      }
>
> -    qemu_wait_io_event_common(cpu);
> -}
> -
> -static void qemu_hvf_wait_io_event(CPUState *cpu)
> -{
> -    while (cpu_thread_is_idle(cpu)) {
> -        qemu_cond_wait(cpu->halt_cond, &qemu_global_mutex);
> +#ifdef _WIN32
> +    /* Eat dummy APC queued by qemu_cpu_kick_thread.  */
> +    if (!tcg_enabled()) {
> +        SleepEx(0, TRUE);
>      }
> +#endif
>      qemu_wait_io_event_common(cpu);
>  }
>
> @@ -1224,7 +1215,7 @@ static void *qemu_kvm_cpu_thread_fn(void *arg)
>                  cpu_handle_guest_debug(cpu);
>              }
>          }
> -        qemu_kvm_wait_io_event(cpu);
> +        qemu_wait_io_event(cpu);
>      } while (!cpu->unplug || cpu_can_run(cpu));
>
>      qemu_kvm_destroy_vcpu(cpu);
> @@ -1270,7 +1261,7 @@ static void *qemu_dummy_cpu_thread_fn(void *arg)
>              exit(1);
>          }
>          qemu_mutex_lock_iothread();
> -        qemu_wait_io_event_common(cpu);
> +        qemu_wait_io_event(cpu);
>      }
>
>      return NULL;
> @@ -1487,7 +1478,7 @@ static void *qemu_tcg_rr_cpu_thread_fn(void *arg)
>              atomic_mb_set(&cpu->exit_request, 0);
>          }
>
> -        qemu_tcg_wait_io_event(cpu ? cpu : QTAILQ_FIRST(&cpus));
> +        qemu_tcg_rr_wait_io_event(cpu ? cpu : QTAILQ_FIRST(&cpus));
>          deal_with_unplugged_cpus();
>      }
>
> @@ -1518,13 +1509,7 @@ static void *qemu_hax_cpu_thread_fn(void *arg)
>              }
>          }
>
> -        while (cpu_thread_is_idle(cpu)) {
> -            qemu_cond_wait(cpu->halt_cond, &qemu_global_mutex);
> -        }
> -#ifdef _WIN32
> -        SleepEx(0, TRUE);
> -#endif
> -        qemu_wait_io_event_common(cpu);
> +        qemu_wait_io_event(cpu);
>      }
>      return NULL;
>  }
> @@ -1561,7 +1546,7 @@ static void *qemu_hvf_cpu_thread_fn(void *arg)
>                  cpu_handle_guest_debug(cpu);
>              }
>          }
> -        qemu_hvf_wait_io_event(cpu);
> +        qemu_wait_io_event(cpu);
>      } while (!cpu->unplug || cpu_can_run(cpu));
>
>      hvf_vcpu_destroy(cpu);
> @@ -1640,7 +1625,7 @@ static void *qemu_tcg_cpu_thread_fn(void *arg)
>          }
>
>          atomic_mb_set(&cpu->exit_request, 0);
> -        qemu_tcg_wait_io_event(cpu);
> +        qemu_wait_io_event(cpu);
>      }
>
>      return NULL;


--
Alex Bennée