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

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

Paolo Bonzini <pbonzini@redhat.com> writes:

> On 04/04/2018 12:34, Alex Bennée wrote:
>>
>> 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>
>
> Isn't this commit db08b687cdd5319286665aabd34f82665630416f?

Doh sorry, that makes even more sense. My check-if-merged script failed
me...

>
> Paolo
>
>>> ---
>>>  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
>>


--
Alex Bennée