[PATCH] KVM: Remove deprecated create_singlethread_workqueue

[Bhaktipriya Shridhar]

The workqueue "irqfd_cleanup_wq" queues a single work item
&irqfd->shutdown and hence doesn't require ordering. It is a host-wide
workqueue for issuing deferred shutdown requests aggregated from all
vm* instances. It is not being used on a memory reclaim path.
Hence, it has been converted to use system_wq.
The work item has been flushed in kvm_irqfd_release().

The workqueue "wqueue" queues a single work item &timer->expired
and hence doesn't require ordering. Also, it is not being used on
a memory reclaim path. Hence, it has been converted to use 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.

Signed-off-by: Bhaktipriya Shridhar <bhaktipriya96 at gmail.com>
---
 virt/kvm/arm/arch_timer.c | 11 ++---------
 virt/kvm/eventfd.c        | 22 +++-------------------
 virt/kvm/kvm_main.c       |  6 ------
 3 files changed, 5 insertions(+), 34 deletions(-)

diff --git a/virt/kvm/arm/arch_timer.c b/virt/kvm/arm/arch_timer.c
index e2d5b6f..56e0c15 100644
--- a/virt/kvm/arm/arch_timer.c
+++ b/virt/kvm/arm/arch_timer.c
@@ -31,7 +31,6 @@
 #include "trace.h"

 static struct timecounter *timecounter;
-static struct workqueue_struct *wqueue;
 static unsigned int host_vtimer_irq;

 void kvm_timer_vcpu_put(struct kvm_vcpu *vcpu)
@@ -140,7 +139,7 @@ static enum hrtimer_restart kvm_timer_expire(struct hrtimer *hrt)
 		return HRTIMER_RESTART;
 	}

-	queue_work(wqueue, &timer->expired);
+	schedule_work(&timer->expired);
 	return HRTIMER_NORESTART;
 }

@@ -455,12 +454,6 @@ int kvm_timer_hyp_init(void)
 		goto out_free;
 	}

-	wqueue = create_singlethread_workqueue("kvm_arch_timer");
-	if (!wqueue) {
-		err = -ENOMEM;
-		goto out_free;
-	}
-
 	kvm_info("virtual timer IRQ%d\n", host_vtimer_irq);
 	on_each_cpu(kvm_timer_init_interrupt, NULL, 1);

@@ -522,7 +515,7 @@ int kvm_timer_enable(struct kvm_vcpu *vcpu)
 	 * VCPUs have the enabled variable set, before entering the guest, if
 	 * the arch timers are enabled.
 	 */
-	if (timecounter && wqueue)
+	if (timecounter)
 		timer->enabled = 1;

 	return 0;
diff --git a/virt/kvm/eventfd.c b/virt/kvm/eventfd.c
index e469b60..f397e9b 100644
--- a/virt/kvm/eventfd.c
+++ b/virt/kvm/eventfd.c
@@ -42,7 +42,6 @@

 #ifdef CONFIG_HAVE_KVM_IRQFD

-static struct workqueue_struct *irqfd_cleanup_wq;

 static void
 irqfd_inject(struct work_struct *work)
@@ -168,7 +167,7 @@ irqfd_deactivate(struct kvm_kernel_irqfd *irqfd)

 	list_del_init(&irqfd->list);

-	queue_work(irqfd_cleanup_wq, &irqfd->shutdown);
+	schedule_work(&irqfd->shutdown);
 }

 int __attribute__((weak)) kvm_arch_set_irq_inatomic(
@@ -555,7 +554,7 @@ kvm_irqfd_deassign(struct kvm *kvm, struct kvm_irqfd *args)
 	 * so that we guarantee there will not be any more interrupts on this
 	 * gsi once this deassign function returns.
 	 */
-	flush_workqueue(irqfd_cleanup_wq);
+	flush_work(&irqfd->shutdown);

 	return 0;
 }
@@ -592,7 +591,7 @@ kvm_irqfd_release(struct kvm *kvm)
 	 * Block until we know all outstanding shutdown jobs have completed
 	 * since we do not take a kvm* reference.
 	 */
-	flush_workqueue(irqfd_cleanup_wq);
+	flush_work(&irqfd->shutdown);

 }

@@ -622,23 +621,8 @@ void kvm_irq_routing_update(struct kvm *kvm)
 	spin_unlock_irq(&kvm->irqfds.lock);
 }

-/*
- * create a host-wide workqueue for issuing deferred shutdown requests
- * aggregated from all vm* instances. We need our own isolated single-thread
- * queue to prevent deadlock against flushing the normal work-queue.
- */
-int kvm_irqfd_init(void)
-{
-	irqfd_cleanup_wq = create_singlethread_workqueue("kvm-irqfd-cleanup");
-	if (!irqfd_cleanup_wq)
-		return -ENOMEM;
-
-	return 0;
-}
-
 void kvm_irqfd_exit(void)
 {
-	destroy_workqueue(irqfd_cleanup_wq);
 }
 #endif

diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index 02e98f3..93506d2 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -3719,12 +3719,7 @@ int kvm_init(void *opaque, unsigned vcpu_size, unsigned vcpu_align,
 	 * kvm_arch_init makes sure there's at most one caller
 	 * for architectures that support multiple implementations,
 	 * like intel and amd on x86.
-	 * kvm_arch_init must be called before kvm_irqfd_init to avoid creating
-	 * conflicts in case kvm is already setup for another implementation.
 	 */
-	r = kvm_irqfd_init();
-	if (r)
-		goto out_irqfd;

 	if (!zalloc_cpumask_var(&cpus_hardware_enabled, GFP_KERNEL)) {
 		r = -ENOMEM;
@@ -3805,7 +3800,6 @@ out_free_0a:
 	free_cpumask_var(cpus_hardware_enabled);
 out_free_0:
 	kvm_irqfd_exit();
-out_irqfd:
 	kvm_arch_exit();
 out_fail:
 	return r;
--
2.1.4