linux-kernel - Re: [PATCH] xen: xen-pciback: Remove create

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Date:	Fri, 27 May 2016 12:01:14 -0400
From:	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
To:	Bhaktipriya Shridhar <bhaktipriya96@...il.com>
Cc:	tj@...nel.org, boris.ostrovsky@...cle.com, david.vrabel@...rix.com,
	jgross@...e.com, JBeulich@...e.com, paul.gortmaker@...driver.com,
	stefano.stabellini@...citrix.com, cardoe@...doe.com,
	xen-devel@...ts.xenproject.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] xen: xen-pciback: Remove create_workqueue

On Fri, May 27, 2016 at 09:24:11PM +0530, Bhaktipriya Shridhar wrote:
> With concurrency managed workqueues, use of dedicated workqueues can be
> replaced by using system_wq. Drop host->intr_wq by using
> system_wq.
> 
> Since there is only a single work item, increase of concurrency level by
> switching to system_wq should not break anything.

_should_ not? Hehe. I presume this has not been tested?
> 
> cancel_work_sync() has been used in xen_pcibk_disconnect() to ensure that
> work item is not pending or executing by the time exit path runs.
> 
> Signed-off-by: Bhaktipriya Shridhar <bhaktipriya96@...il.com>
> ---
>  drivers/xen/xen-pciback/pciback.h     |  1 -
>  drivers/xen/xen-pciback/pciback_ops.c |  2 +-
>  drivers/xen/xen-pciback/xenbus.c      | 10 +---------
>  3 files changed, 2 insertions(+), 11 deletions(-)
> 
> diff --git a/drivers/xen/xen-pciback/pciback.h b/drivers/xen/xen-pciback/pciback.h
> index 4d529f3..7af369b6 100644
> --- a/drivers/xen/xen-pciback/pciback.h
> +++ b/drivers/xen/xen-pciback/pciback.h
> @@ -55,7 +55,6 @@ struct xen_pcibk_dev_data {
> 
>  /* Used by XenBus and xen_pcibk_ops.c */
>  extern wait_queue_head_t xen_pcibk_aer_wait_queue;
> -extern struct workqueue_struct *xen_pcibk_wq;
>  /* Used by pcistub.c and conf_space_quirks.c */
>  extern struct list_head xen_pcibk_quirks;
> 
> diff --git a/drivers/xen/xen-pciback/pciback_ops.c b/drivers/xen/xen-pciback/pciback_ops.c
> index 2f19dd7..f8c7775 100644
> --- a/drivers/xen/xen-pciback/pciback_ops.c
> +++ b/drivers/xen/xen-pciback/pciback_ops.c
> @@ -310,7 +310,7 @@ void xen_pcibk_test_and_schedule_op(struct xen_pcibk_device *pdev)
>  	 * already processing a request */
>  	if (test_bit(_XEN_PCIF_active, (unsigned long *)&pdev->sh_info->flags)
>  	    && !test_and_set_bit(_PDEVF_op_active, &pdev->flags)) {
> -		queue_work(xen_pcibk_wq, &pdev->op_work);
> +		schedule_work(&pdev->op_work);
>  	}
>  	/*_XEN_PCIB_active should have been cleared by pcifront. And also make
>  	sure xen_pcibk is waiting for ack by checking _PCIB_op_pending*/
> diff --git a/drivers/xen/xen-pciback/xenbus.c b/drivers/xen/xen-pciback/xenbus.c
> index c252eb3..f70a8e1 100644
> --- a/drivers/xen/xen-pciback/xenbus.c
> +++ b/drivers/xen/xen-pciback/xenbus.c
> @@ -17,7 +17,6 @@
>  #include "pciback.h"
> 
>  #define INVALID_EVTCHN_IRQ  (-1)
> -struct workqueue_struct *xen_pcibk_wq;
> 
>  static bool __read_mostly passthrough;
>  module_param(passthrough, bool, S_IRUGO);
> @@ -76,8 +75,7 @@ static void xen_pcibk_disconnect(struct xen_pcibk_device *pdev)
>  	/* If the driver domain started an op, make sure we complete it
>  	 * before releasing the shared memory */
> 
> -	/* Note, the workqueue does not use spinlocks at all.*/
> -	flush_workqueue(xen_pcibk_wq);
> +	cancel_work_sync(&pdev->op_work);
> 
>  	if (pdev->sh_info != NULL) {
>  		xenbus_unmap_ring_vfree(pdev->xdev, pdev->sh_info);
> @@ -733,11 +731,6 @@ const struct xen_pcibk_backend *__read_mostly xen_pcibk_backend;
> 
>  int __init xen_pcibk_xenbus_register(void)
>  {
> -	xen_pcibk_wq = create_workqueue("xen_pciback_workqueue");
> -	if (!xen_pcibk_wq) {
> -		pr_err("%s: create xen_pciback_workqueue failed\n", __func__);
> -		return -EFAULT;
> -	}
>  	xen_pcibk_backend = &xen_pcibk_vpci_backend;
>  	if (passthrough)
>  		xen_pcibk_backend = &xen_pcibk_passthrough_backend;
> @@ -747,6 +740,5 @@ int __init xen_pcibk_xenbus_register(void)
> 
>  void __exit xen_pcibk_xenbus_unregister(void)
>  {
> -	destroy_workqueue(xen_pcibk_wq);
>  	xenbus_unregister_driver(&xen_pcibk_driver);
>  }
> --
> 2.1.4
>