xen: xen-pciback: Remove create_workqueue

PATCH In review Bhaktipriya Shridhar 4 participants 8 messages May 27, 2016 – May 31, 2016 Xen hypervisor interface

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Konrad Rzeszutek Wilk

2016-05-27 16:01 UTC #1 lore raw

Quoted 6 lines · Bhaktipriya Shridhar

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?

Quoted 78 lines

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 <[email protected]>

---
 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(-)

drivers/xen/xen-pciback/pciback.h +0 -1

index 4d529f3..7af369b6 100644
@@ -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;

drivers/xen/xen-pciback/pciback_ops.c +1 -1

index 2f19dd7..f8c7775 100644
@@ -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*/

drivers/xen/xen-pciback/xenbus.c +1 ~~-10~~

index c252eb3..f70a8e1 100644
@@ -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);
 }
--

Quoted 2 lines

2.1.4

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Tejun Heo

2016-05-27 16:08 UTC #3 lore raw

Hello,

Quoted 3 lines · Konrad Rzeszutek Wilk

Quoted 2 lines · Bhaktipriya Shridhar
With concurrency managed workqueues, use of dedicated workqueues can be replaced by using system_wq. Drop host->intr_wq by using

                                      ^
				      xen_pcibk_wq

Quoted 6 lines

Quoted 4 lines
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?

Yeah, this is a part of sweeping conversions and it's challenging (and often impossible for specific drivers) to setup test environments. xen isn't as bad but can still be a pretty specialized setup. The conversions aren't high risk and shouldn't be too difficult to root cause when something goes south. We'd greatly appreciate any helps with reviewing and testing.

Quoted 11 lines

drivers/xen/xen-pciback/xenbus.c static void xen_pcibk_disconnect(struct xen_pcibk_device *pdev) · line 78
Quoted 11 lines
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 <[email protected]>
drivers/xen/xen-pciback/xenbus.c +1 -2
@@ -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);

Should it be flush_work() instead? Is it okay for a pdev->op_work to be queued and canceled without actually getting executed?

Thanks.

Signature · 1 line

tejun

Konrad Rzeszutek Wilk

2016-05-27 16:32 UTC #4 lore raw

Quoted 30 lines · Tejun Heo

Hello,
Quoted 3 lines · Konrad Rzeszutek Wilk
Quoted 2 lines · Bhaktipriya Shridhar
With concurrency managed workqueues, use of dedicated workqueues can be replaced by using system_wq. Drop host->intr_wq by using
                                      ^
				      xen_pcibk_wq
Quoted 6 lines
Quoted 4 lines
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?
Yeah, this is a part of sweeping conversions and it's challenging (and often impossible for specific drivers) to setup test environments. xen isn't as bad but can still be a pretty specialized setup. The conversions aren't high risk and shouldn't be too difficult to root cause when something goes south. We'd greatly appreciate any helps with reviewing and testing.
Quoted 8 lines
Quoted 8 lines
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 <[email protected]>
drivers/xen/xen-pciback/xenbus.c +0 -0
@@ -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 */
 

Quoted 6 lines

Quoted 3 lines
drivers/xen/xen-pciback/xenbus.c static void xen_pcibk_disconnect(struct xen_pcibk_device *pdev) · line 78
Quoted 3 lines
drivers/xen/xen-pciback/xenbus.c +1 -2
-	/* Note, the workqueue does not use spinlocks at all.*/
-	flush_workqueue(xen_pcibk_wq);
+	cancel_work_sync(&pdev->op_work);
Should it be flush_work() instead? Is it okay for a pdev->op_work to be queued and canceled without actually getting executed?

It should really flush them. The comment above says so, but in reality it does not matter that much as we tearing down the communication. As long as the pdev->op_work either completes or is never executed - we are fine.

Quoted 5 lines

Thanks.
Signature · 1 line
tejun

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David Vrabel

2016-05-31 10:12 UTC #5 lore raw

Quoted 38 lines · Konrad Rzeszutek Wilk

Quoted 30 lines · Tejun Heo
Hello,
Quoted 3 lines · Konrad Rzeszutek Wilk
Quoted 2 lines · Bhaktipriya Shridhar
With concurrency managed workqueues, use of dedicated workqueues can be replaced by using system_wq. Drop host->intr_wq by using
                                      ^
				      xen_pcibk_wq
Quoted 6 lines
Quoted 4 lines
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?
Yeah, this is a part of sweeping conversions and it's challenging (and often impossible for specific drivers) to setup test environments. xen isn't as bad but can still be a pretty specialized setup. The conversions aren't high risk and shouldn't be too difficult to root cause when something goes south. We'd greatly appreciate any helps with reviewing and testing.
Quoted 8 lines
Quoted 8 lines
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 <[email protected]>
drivers/xen/xen-pciback/xenbus.c +0 -0
@@ -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 */
 
Quoted 6 lines
Quoted 3 lines
drivers/xen/xen-pciback/xenbus.c static void xen_pcibk_disconnect(struct xen_pcibk_device *pdev) · line 78
Quoted 3 lines
drivers/xen/xen-pciback/xenbus.c +1 -2
-	/* Note, the workqueue does not use spinlocks at all.*/
-	flush_workqueue(xen_pcibk_wq);
+	cancel_work_sync(&pdev->op_work);
Should it be flush_work() instead? Is it okay for a pdev->op_work to be queued and canceled without actually getting executed?

Quoted 3 lines

It should really flush them. The comment above says so, but in reality it does not matter that much as we tearing down the communication. As long as the pdev->op_work either completes or is never executed - we are fine.

The comment should be updated to reflect this.

David

David Vrabel

2016-05-31 10:12 UTC #6 lore raw

In reply to Konrad Rzeszutek Wilk

Quoted 38 lines · Konrad Rzeszutek Wilk

Quoted 30 lines · Tejun Heo
Hello,
Quoted 3 lines · Konrad Rzeszutek Wilk
Quoted 2 lines · Bhaktipriya Shridhar
With concurrency managed workqueues, use of dedicated workqueues can be replaced by using system_wq. Drop host->intr_wq by using
                                      ^
				      xen_pcibk_wq
Quoted 6 lines
Quoted 4 lines
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?
Yeah, this is a part of sweeping conversions and it's challenging (and often impossible for specific drivers) to setup test environments. xen isn't as bad but can still be a pretty specialized setup. The conversions aren't high risk and shouldn't be too difficult to root cause when something goes south. We'd greatly appreciate any helps with reviewing and testing.
Quoted 8 lines
Quoted 8 lines
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 <[email protected]>
drivers/xen/xen-pciback/xenbus.c +0 -0
@@ -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 */
 
Quoted 6 lines
Quoted 3 lines
drivers/xen/xen-pciback/xenbus.c static void xen_pcibk_disconnect(struct xen_pcibk_device *pdev) · line 78
Quoted 3 lines
drivers/xen/xen-pciback/xenbus.c +1 -2
-	/* Note, the workqueue does not use spinlocks at all.*/
-	flush_workqueue(xen_pcibk_wq);
+	cancel_work_sync(&pdev->op_work);
Should it be flush_work() instead? Is it okay for a pdev->op_work to be queued and canceled without actually getting executed?

Quoted 3 lines

It should really flush them. The comment above says so, but in reality it does not matter that much as we tearing down the communication. As long as the pdev->op_work either completes or is never executed - we are fine.

The comment should be updated to reflect this.

David

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Xen-devel mailing list
[email protected]
http://lists.xen.org/xen-devel

Tejun Heo

2016-05-27 16:08 UTC #7 lore raw

In reply to Konrad Rzeszutek Wilk

Hello,

Quoted 3 lines · Konrad Rzeszutek Wilk

Quoted 2 lines · Bhaktipriya Shridhar
With concurrency managed workqueues, use of dedicated workqueues can be replaced by using system_wq. Drop host->intr_wq by using

                                      ^
				      xen_pcibk_wq

Quoted 6 lines

Quoted 4 lines
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?

Quoted 11 lines

drivers/xen/xen-pciback/xenbus.c static void xen_pcibk_disconnect(struct xen_pcibk_device *pdev) · line 78
Quoted 11 lines
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 <[email protected]>
drivers/xen/xen-pciback/xenbus.c +1 -2
@@ -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);

Should it be flush_work() instead? Is it okay for a pdev->op_work to be queued and canceled without actually getting executed?

Thanks.

Signature · 6 lines

tejun

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