Re: [Qemu-devel] [PATCH v3 2/5] util: introduce threaded workqueue

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

On 11/24/18 8:17 AM, Emilio G. Cota wrote:
> On Thu, Nov 22, 2018 at 15:20:25 +0800, guangrong.xiao@gmail.com wrote:
>> +static uint64_t get_free_request_bitmap(Threads *threads, ThreadLocal *thread)
>> +{
>> +    uint64_t request_fill_bitmap, request_done_bitmap, result_bitmap;
>> +
>> +    request_fill_bitmap = atomic_rcu_read(&thread->request_fill_bitmap);
>> +    request_done_bitmap = atomic_rcu_read(&thread->request_done_bitmap);
>> +    bitmap_xor(&result_bitmap, &request_fill_bitmap, &request_done_bitmap,
>> +               threads->thread_requests_nr);
> 
> This is not wrong, but it's a big ugly. Instead, I would:
> 
> - Introduce bitmap_xor_atomic in a previous patch
> - Use bitmap_xor_atomic here, getting rid of the rcu reads

Hmm, however, we do not need atomic xor operation here... that should be slower than
just two READ_ONCE calls.