Re: [Qemu-devel] [PATCH 10/12] migration: introduce lockless multithreads model

[Xiao Guangrong <guangrong.xiao@gmail.com>]

On 07/14/2018 12:24 AM, Dr. David Alan Gilbert wrote:

>>> +static void *thread_run(void *opaque)
>>> +{
>>> +    ThreadLocal *self_data = (ThreadLocal *)opaque;
>>> +    Threads *threads = self_data->threads;
>>> +    void (*handler)(ThreadRequest *data) = threads->thread_request_handler;
>>> +    ThreadRequest *request;
>>> +    int count, ret;
>>> +
>>> +    for ( ; !atomic_read(&self_data->quit); ) {
>>> +        qemu_event_reset(&self_data->ev);
>>> +
>>> +        count = 0;
>>> +        while ((request = ring_get(self_data->request_ring)) ||
>>> +            count < BUSY_WAIT_COUNT) {
>>> +             /*
>>> +             * wait some while before go to sleep so that the user
>>> +             * needn't go to kernel space to wake up the consumer
>>> +             * threads.
>>> +             *
>>> +             * That will waste some CPU resource indeed however it
>>> +             * can significantly improve the case that the request
>>> +             * will be available soon.
>>> +             */
>>> +             if (!request) {
>>> +                cpu_relax();
>>> +                count++;
>>> +                continue;
>>> +            }
>>> +            count = 0;
> 
> Things like busywait counts probably need isolating somewhere;
> getting those counts right is quite hard.

Okay, i will make it to be a separated function.