linux-kernel - Re: [PATCH] spi: spi-sh: Remove deprecated create_singlethread

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Date:	Sat, 16 Jul 2016 13:36:17 +0530
From:	Bhaktipriya Shridhar <bhaktipriya96@...il.com>
To:	Mark Brown <broonie@...nel.org>
Cc:	linux-spi@...r.kernel.org,
	"Linux-Kernel@...r. Kernel. Org" <linux-kernel@...r.kernel.org>,
	Tejun Heo <tj@...nel.org>
Subject: Re: [PATCH] spi: spi-sh: Remove deprecated create_singlethread_workqueue

Please ignore this mail. I have already sent a patch for this driver

Thanks,
Bhaktipriya


On Sat, Jul 16, 2016 at 1:35 PM, Bhaktipriya Shridhar
<bhaktipriya96@...il.com> wrote:
> The workqueue has a single workitem(&ss->ws) and hence doesn't require
> ordering. Also, it is not being used on a memory reclaim path. Hence, the
> singlethreaded workqueue has been replaced with the use of system_wq.
>
> 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.
>
> Work item has been flushed in spi_sh_remove() to ensure that
> there are no pending tasks while disconnecting the driver.
>
> Signed-off-by: Bhaktipriya Shridhar <bhaktipriya96@...il.com>
> ---
>  drivers/spi/spi-sh.c | 16 +++-------------
>  1 file changed, 3 insertions(+), 13 deletions(-)
>
> diff --git a/drivers/spi/spi-sh.c b/drivers/spi/spi-sh.c
> index 5025011..2bf53f0 100644
> --- a/drivers/spi/spi-sh.c
> +++ b/drivers/spi/spi-sh.c
> @@ -82,7 +82,6 @@ struct spi_sh_data {
>         int irq;
>         struct spi_master *master;
>         struct list_head queue;
> -       struct workqueue_struct *workqueue;
>         struct work_struct ws;
>         unsigned long cr1;
>         wait_queue_head_t wait;
> @@ -380,7 +379,7 @@ static int spi_sh_transfer(struct spi_device *spi, struct spi_message *mesg)
>         spi_sh_clear_bit(ss, SPI_SH_SSA, SPI_SH_CR1);
>
>         list_add_tail(&mesg->queue, &ss->queue);
> -       queue_work(ss->workqueue, &ss->ws);
> +       schedule_work(&ss->ws);
>
>         spin_unlock_irqrestore(&ss->lock, flags);
>
> @@ -425,7 +424,7 @@ static int spi_sh_remove(struct platform_device *pdev)
>         struct spi_sh_data *ss = platform_get_drvdata(pdev);
>
>         spi_unregister_master(ss->master);
> -       destroy_workqueue(ss->workqueue);
> +       flush_work(&ss->ws);
>         free_irq(ss->irq, ss);
>
>         return 0;
> @@ -484,18 +483,11 @@ static int spi_sh_probe(struct platform_device *pdev)
>         spin_lock_init(&ss->lock);
>         INIT_WORK(&ss->ws, spi_sh_work);
>         init_waitqueue_head(&ss->wait);
> -       ss->workqueue = create_singlethread_workqueue(
> -                                       dev_name(master->dev.parent));
> -       if (ss->workqueue == NULL) {
> -               dev_err(&pdev->dev, "create workqueue error\n");
> -               ret = -EBUSY;
> -               goto error1;
> -       }
>
>         ret = request_irq(irq, spi_sh_irq, 0, "spi_sh", ss);
>         if (ret < 0) {
>                 dev_err(&pdev->dev, "request_irq error\n");
> -               goto error2;
> +               goto error1;
>         }
>
>         master->num_chipselect = 2;
> @@ -514,8 +506,6 @@ static int spi_sh_probe(struct platform_device *pdev)
>
>   error3:
>         free_irq(irq, ss);
> - error2:
> -       destroy_workqueue(ss->workqueue);
>   error1:
>         spi_master_put(master);
>
> --
> 2.1.4
>