Re: [RFC] io-wq: decouple work_list protection from the big wqe->lock

[Hao Xu <haoxu@linux.alibaba.com>]

在 2021/11/4 上午3:10, Jens Axboe 写道:
> On 10/31/21 4:49 AM, Hao Xu wrote:
>> @@ -380,10 +382,14 @@ static void io_wqe_dec_running(struct io_worker *worker)
>>   	if (!(worker->flags & IO_WORKER_F_UP))
>>   		return;
>>   
>> +	raw_spin_lock(&acct->lock);
>>   	if (atomic_dec_and_test(&acct->nr_running) && io_acct_run_queue(acct)) {
>> +		raw_spin_unlock(&acct->lock);
>>   		atomic_inc(&acct->nr_running);
>>   		atomic_inc(&wqe->wq->worker_refs);
>>   		io_queue_worker_create(worker, acct, create_worker_cb);
>> +	} else {
>> +		raw_spin_unlock(&acct->lock);
>>   	}
>>   }
> 
> I think this may be more readable as:
> 
> static void io_wqe_dec_running(struct io_worker *worker)
> 	__must_hold(wqe->lock)
> {
> 	struct io_wqe_acct *acct = io_wqe_get_acct(worker);
> 	struct io_wqe *wqe = worker->wqe;
> 
> 	if (!(worker->flags & IO_WORKER_F_UP))
> 		return;
> 	if (!atomic_dec_and_test(&acct->nr_running))
> 		return;
> 
> 	raw_spin_lock(&acct->lock);
> 	if (!io_acct_run_queue(acct)) {
> 		raw_spin_unlock(&acct->lock);
> 		return;
> 	}
> 
> 	raw_spin_unlock(&acct->lock);
> 	atomic_inc(&acct->nr_running);
> 	atomic_inc(&wqe->wq->worker_refs);
> 	io_queue_worker_create(worker, acct, create_worker_cb);
> }
> 
> ?
> 
> Patch looks pretty sane to me, but there's a lot of lock shuffling going
> on for it. Like in io_worker_handle_work(), and particularly in
> io_worker_handle_work(). I think it'd be worthwhile to spend some time
> to see if that could be improved. These days, lock contention is more
> about frequency of lock grabbing rather than hold time. Maybe clean
> nesting of wqe->lock -> acct->lock (which would be natural) can help
> that?
Sure, I'm working on reduce the lock contension further, will
update it and send the whole patchset later.

Regards,
Hao
>