[PATCH v2 3/3] kvm tools: stop virtio console doing unnecessary input handling

[Jonathan Austin <jonathan.austin@arm.com>]

The asynchronous nature of the virtio input handling (using a job queue)
can result in unnecessary jobs being created if there is some delay in
handing input (the original function to handle the input returns immediately
without the file having been read, and hence poll returns immediately
informing us of data to read).

This patch adds synchronisation to the threads so that we don't start
polling input files again until we've read from the console.

Signed-off-by: Jonathan Austin <jonathan.austin@arm.com>
Acked-by: Marc Zyngier <marc.zyngier@arm.com>
---
 tools/kvm/virtio/console.c |   23 ++++++++++++++++++++---
 1 file changed, 20 insertions(+), 3 deletions(-)

diff --git a/tools/kvm/virtio/console.c b/tools/kvm/virtio/console.c
index 83c58bf..f982dab7 100644
--- a/tools/kvm/virtio/console.c
+++ b/tools/kvm/virtio/console.c
@@ -36,12 +36,17 @@ struct con_dev {
 	struct virtio_console_config	config;
 	u32				features;
 
+	pthread_cond_t			poll_cond;
+	int				vq_ready;
+
 	struct thread_pool__job		jobs[VIRTIO_CONSOLE_NUM_QUEUES];
 };
 
 static struct con_dev cdev = {
 	.mutex				= MUTEX_INITIALIZER,
 
+	.vq_ready			= 0,
+
 	.config = {
 		.cols			= 80,
 		.rows			= 24,
@@ -69,6 +74,9 @@ static void virtio_console__inject_interrupt_callback(struct kvm *kvm, void *par
 
 	vq = param;
 
+	if (!cdev.vq_ready)
+		pthread_cond_wait(&cdev.poll_cond, &cdev.mutex.mutex);
+
 	if (term_readable(0) && virt_queue__available(vq)) {
 		head = virt_queue__get_iov(vq, iov, &out, &in, kvm);
 		len = term_getc_iov(kvm, iov, in, 0);
@@ -81,7 +89,8 @@ static void virtio_console__inject_interrupt_callback(struct kvm *kvm, void *par
 
 void virtio_console__inject_interrupt(struct kvm *kvm)
 {
-	thread_pool__do_job(&cdev.jobs[VIRTIO_CONSOLE_RX_QUEUE]);
+	virtio_console__inject_interrupt_callback(kvm,
+					&cdev.vqs[VIRTIO_CONSOLE_RX_QUEUE]);
 }
 
 static void virtio_console_handle_callback(struct kvm *kvm, void *param)
@@ -141,10 +150,16 @@ static int init_vq(struct kvm *kvm, void *dev, u32 vq, u32 page_size, u32 align,
 
 	vring_init(&queue->vring, VIRTIO_CONSOLE_QUEUE_SIZE, p, align);
 
-	if (vq == VIRTIO_CONSOLE_TX_QUEUE)
+	if (vq == VIRTIO_CONSOLE_TX_QUEUE) {
 		thread_pool__init_job(&cdev.jobs[vq], kvm, virtio_console_handle_callback, queue);
-	else if (vq == VIRTIO_CONSOLE_RX_QUEUE)
+	} else if (vq == VIRTIO_CONSOLE_RX_QUEUE) {
 		thread_pool__init_job(&cdev.jobs[vq], kvm, virtio_console__inject_interrupt_callback, queue);
+		/* Tell the waiting poll thread that we're ready to go */
+		mutex_lock(&cdev.mutex);
+		cdev.vq_ready = 1;
+		pthread_cond_signal(&cdev.poll_cond);
+		mutex_unlock(&cdev.mutex);
+	}
 
 	return 0;
 }
@@ -192,6 +207,8 @@ int virtio_console__init(struct kvm *kvm)
 	if (kvm->cfg.active_console != CONSOLE_VIRTIO)
 		return 0;
 
+	pthread_cond_init(&cdev.poll_cond, NULL);
+
 	virtio_init(kvm, &cdev, &cdev.vdev, &con_dev_virtio_ops,
 		    VIRTIO_DEFAULT_TRANS, PCI_DEVICE_ID_VIRTIO_CONSOLE,
 		    VIRTIO_ID_CONSOLE, PCI_CLASS_CONSOLE);
-- 
1.7.9.5