Re: [PATCH 05/11] io-wq: add a new parameter for creating a new fixed worker

[Pavel Begunkov <asml.silence@gmail.com>]

On 6/9/23 13:20, Hao Xu wrote:
> From: Hao Xu <howeyxu@tencent.com>
> 
> Add a new parameter when creating new workers to indicate if users
> want a normal or fixed worker.
> 
> Signed-off-by: Hao Xu <howeyxu@tencent.com>
> ---
>   io_uring/io-wq.c | 33 ++++++++++++++++++++-------------
>   1 file changed, 20 insertions(+), 13 deletions(-)
> 
> diff --git a/io_uring/io-wq.c b/io_uring/io-wq.c
> index bf9e9af8d9ca..048856eef4d4 100644
> --- a/io_uring/io-wq.c
> +++ b/io_uring/io-wq.c
[...]
>   
> +static bool is_fixed_worker(struct io_worker *worker)
> +{
> +	return worker->flags & IO_WORKER_F_FIXED;
> +} 

That's what I mentioned in the other comment.

> +
>   static void create_worker_cb(struct callback_head *cb)
>   {
>   	struct io_worker *worker;
> @@ -331,7 +337,7 @@ static void create_worker_cb(struct callback_head *cb)
>   	}
>   	raw_spin_unlock(&wq->lock);
>   	if (do_create) {
> -		create_io_worker(wq, worker->create_index);
> +		create_io_worker(wq, worker->create_index, is_fixed_worker(worker));
>   	} else {
>   		atomic_dec(&acct->nr_running);
>   		io_worker_ref_put(wq);
> @@ -398,6 +404,8 @@ static void io_wq_dec_running(struct io_worker *worker)
>   		return;
>   	if (!io_acct_run_queue(acct))
>   		return;
> +	if (is_fixed_worker(worker))
> +		return;

Aha, it's here. I was thinking about it a little bit more.
Is it even correct? If you have a mixed fixed/non-fixed setup
you presumably want non-fixed workers to kick in such situations.
I don't remember this creation voodoo well, maybe Jens does have
an idea.

>   
>   	atomic_inc(&acct->nr_running);
>   	atomic_inc(&wq->worker_refs);
> @@ -601,11 +609,6 @@ static bool is_worker_exiting(struct io_worker *worker)
>   	return worker->flags & IO_WORKER_F_EXIT;
>   }
[...]
> -static bool create_io_worker(struct io_wq *wq, int index)
> +static bool create_io_worker(struct io_wq *wq, int index, bool fixed)
>   {
>   	struct io_wq_acct *acct = &wq->acct[index];
>   	struct io_worker *worker;
> @@ -833,10 +836,14 @@ static bool create_io_worker(struct io_wq *wq, int index)
>   	if (index == IO_WQ_ACCT_BOUND)
>   		worker->flags |= IO_WORKER_F_BOUND;
>   
> +	if (fixed)
> +		worker->flags |= IO_WORKER_F_FIXED;
> +
>   	tsk = create_io_thread(io_wq_worker, worker, NUMA_NO_NODE);
>   	if (!IS_ERR(tsk)) {
> -		io_init_new_worker(wq, worker, tsk);
> -	} else if (!io_should_retry_thread(PTR_ERR(tsk))) {
> +		if (!fixed)
> +			io_init_new_worker(wq, worker, tsk);

Why do we skip io_init_new_worker()? I assume you putting it
into lists, but what about the rest? I.e.

	tsk->worker_private = worker;
	worker->task = tsk;
	set_cpus_allowed_ptr(tsk, wq->cpu_mask);


> +	} else if (fixed || !io_should_retry_thread(PTR_ERR(tsk))) {
>   		kfree(worker);
>   		goto fail;
>   	} else {
> @@ -947,7 +954,7 @@ void io_wq_enqueue(struct io_wq *wq, struct io_wq_work *work)
>   	    !atomic_read(&acct->nr_running))) {
>   		bool did_create;
>   
> -		did_create = io_wq_create_worker(wq, acct);
> +		did_create = io_wq_create_worker(wq, acct, false);
>   		if (likely(did_create))
>   			return;

-- 
Pavel Begunkov