linux-kernel - Re: [PATCH] net/mlx5_core/health: Remove deprecated create_singlethread

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Date:	Sun, 17 Jul 2016 08:13:27 +0300
From:	Leon Romanovsky <leonro@...lanox.com>
To:	Bhaktipriya Shridhar <bhaktipriya96@...il.com>
Cc:	Matan Barak <matanb@...lanox.com>, netdev@...r.kernel.org,
	linux-rdma@...r.kernel.org, linux-kernel@...r.kernel.org,
	Tejun Heo <tj@...nel.org>
Subject: Re: [PATCH] net/mlx5_core/health: Remove deprecated
 create_singlethread_workqueue

On Sat, Jul 16, 2016 at 01:29:20PM +0530, Bhaktipriya Shridhar wrote:
> The workqueue health->wq was used as per device private health thread.
> This was done so that system error handling could be processed
> concurrently.

Not exactly, AFAIK it was intended to perform delayed work and not
relevant to concurrency.

> The workqueue has a single workitem(&health->work) and
> hence doesn't require ordering. It is involved in handling the health of
> the deviceand is not being used on a memory reclaim path.
> Hence, the singlethreaded workqueue has been replaced with the use of
> system_wq.

Yes

> 
> System workqueues have been able to handle high level of concurrency
> for a long time now and hence it's not required to have a singlethreaded
> workqueue just to gain concurrency. Unlike a dedicated per-cpu workqueue
> created with create_singlethread_workqueue(), system_wq allows multiple
> work items to overlap executions even on the same CPU; however, a
> per-cpu workqueue doesn't have any CPU locality or global ordering
> guarantee unless the target CPU is explicitly specified and thus the
> increase of local concurrency shouldn't make any difference.

Not relevant.

> 
> Work item has been flushed in mlx5_health_cleanup() to ensure that
> there are no pending tasks while disconnecting the driver.
> 
> Signed-off-by: Bhaktipriya Shridhar <bhaktipriya96@...il.com>
> ---
>  drivers/net/ethernet/mellanox/mlx5/core/health.c | 7 ++-----
>  1 file changed, 2 insertions(+), 5 deletions(-)
> 
> diff --git a/drivers/net/ethernet/mellanox/mlx5/core/health.c b/drivers/net/ethernet/mellanox/mlx5/core/health.c
> index 42d16b9..9acbccf 100644
> --- a/drivers/net/ethernet/mellanox/mlx5/core/health.c
> +++ b/drivers/net/ethernet/mellanox/mlx5/core/health.c
> @@ -267,7 +267,7 @@ static void poll_health(unsigned long data)
>  	if (in_fatal(dev) && !health->sick) {
>  		health->sick = true;
>  		print_health_info(dev);
> -		queue_work(health->wq, &health->work);
> +		schedule_work(&health->work);
>  	}
>  }
> 
> @@ -296,7 +296,7 @@ void mlx5_health_cleanup(struct mlx5_core_dev *dev)
>  {
>  	struct mlx5_core_health *health = &dev->priv.health;
> 
> -	destroy_workqueue(health->wq);
> +	flush_work(&health->work);
>  }
> 
>  int mlx5_health_init(struct mlx5_core_dev *dev)
> @@ -311,10 +311,7 @@ int mlx5_health_init(struct mlx5_core_dev *dev)
> 
>  	strcpy(name, "mlx5_health");
>  	strcat(name, dev_name(&dev->pdev->dev));
> -	health->wq = create_singlethread_workqueue(name);
>  	kfree(name);

You need to remove "name" initialization/usage too.
It is not needed.

> -	if (!health->wq)
> -		return -ENOMEM;
> 
>  	INIT_WORK(&health->work, health_care);
> 
> --
> 2.1.4
> 
> --
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