Re: [RFC PATCH v2 2/6] migration/multifd: Stop checking p->quit in multifd_send_thread

[Juan Quintela]

Fabiano Rosas <farosas@suse.de> wrote:
> Juan Quintela <quintela@redhat.com> writes:
>
>> Fabiano Rosas <farosas@suse.de> wrote:
>>> We don't need to check p->quit in the multifd_send_thread() because it
>>> is shadowed by the 'exiting' flag. Ever since that flag was added
>>> p->quit became obsolete as a way to stop the thread.
>>>
>>> Since p->quit is set at multifd_send_terminate_threads() under the
>>> p->mutex lock, the thread will only see it once it loops, so 'exiting'
>>> will always be seen first.
>>>
>>> Note that setting p->quit at multifd_send_terminate_threads() still
>>> makes sense because we need a way to inform multifd_send_pages() that
>>> the channel has stopped.
>>>
>>> Signed-off-by: Fabiano Rosas <farosas@suse.de>
>>
>> Reviewed-by: Juan Quintela <quintela@redhat.com>
>>
>> But then should we remove the quit altogether?
>>
>
> It still serves a purpose to allow multifd_send_pages() to see that the
> channel has exited. While that function does also check
> multifd_send_state->exiting, it could already be waiting at the mutex
> when the channel aborts. So we need to either check 'exiting' again or
> keep p->quit.

At the point that we are putting p->quit = true, we are really next to
where we put p->running = false.

I think we can move to use only p->running.

Later, Juan.