Re: [Qemu-devel] [PATCH 11/15] lock: introduce global lock for device tree

[Paolo Bonzini <pbonzini@redhat.com>]

Il 09/08/2012 09:28, liu ping fan ha scritto:
> On Wed, Aug 8, 2012 at 5:41 PM, Paolo Bonzini <pbonzini@redhat.com> wrote:
>> Il 08/08/2012 08:25, Liu Ping Fan ha scritto:
>>> From: Liu Ping Fan <pingfank@linux.vnet.ibm.com>
>>>
>>> Signed-off-by: Liu Ping Fan <pingfank@linux.vnet.ibm.com>
>>> ---
>>>  cpus.c      |   12 ++++++++++++
>>>  main-loop.h |    3 +++
>>>  2 files changed, 15 insertions(+), 0 deletions(-)
>>>
>>> diff --git a/cpus.c b/cpus.c
>>> index b182b3d..a734b36 100644
>>> --- a/cpus.c
>>> +++ b/cpus.c
>>> @@ -611,6 +611,7 @@ static void qemu_tcg_init_cpu_signals(void)
>>>  }
>>>  #endif /* _WIN32 */
>>>
>>> +QemuMutex qemu_device_tree_mutex;
>>>  QemuMutex qemu_global_mutex;
>>>  static QemuCond qemu_io_proceeded_cond;
>>>  static bool iothread_requesting_mutex;
>>> @@ -634,6 +635,7 @@ void qemu_init_cpu_loop(void)
>>>      qemu_cond_init(&qemu_work_cond);
>>>      qemu_cond_init(&qemu_io_proceeded_cond);
>>>      qemu_mutex_init(&qemu_global_mutex);
>>> +    qemu_mutex_init(&qemu_device_tree_mutex);
>>>
>>>      qemu_thread_get_self(&io_thread);
>>>  }
>>> @@ -911,6 +913,16 @@ void qemu_mutex_unlock_iothread(void)
>>>      qemu_mutex_unlock(&qemu_global_mutex);
>>>  }
>>>
>>> +void qemu_lock_devtree(void)
>>> +{
>>> +    qemu_mutex_lock(&qemu_device_tree_mutex);
>>> +}
>>> +
>>> +void qemu_unlock_devtree(void)
>>> +{
>>> +    qemu_mutex_unlock(&qemu_device_tree_mutex);
>>> +}
>>
>> We don't need the wrappers.  They are there for the big lock just
>> because TCG needs extra work for iothread_requesting_mutex.
>>
> Sorry, could you give more detail about TCG, what is extra work.

void qemu_mutex_lock_iothread(void)
{
    if (!tcg_enabled()) {
        qemu_mutex_lock(&qemu_global_mutex);
    } else {
        iothread_requesting_mutex = true;
        if (qemu_mutex_trylock(&qemu_global_mutex)) {
            qemu_cpu_kick_thread(first_cpu);
            qemu_mutex_lock(&qemu_global_mutex);
        }
        iothread_requesting_mutex = false;
        qemu_cond_broadcast(&qemu_io_proceeded_cond);
    }
}

You do not need any of the code in the "else" branch for the device tree
mutex, so you do not need wrappers.