Commit 744583ec authored by Gerd Hoffmann's avatar Gerd Hoffmann
Browse files

drm/virtio: notify virtqueues without holding spinlock 



Split virtqueue_kick() call into virtqueue_kick_prepare(), which
requires serialization, and virtqueue_notify(), which does not.  Move
the virtqueue_notify() call out of the critical section protected by the
queue lock.  This avoids triggering a vmexit while holding the lock and
thereby fixes a rather bad spinlock contention.

Suggested-by: default avatarChia-I Wu <olvaffe@gmail.com>
Signed-off-by: default avatarGerd Hoffmann <kraxel@redhat.com>
Reviewed-by: default avatarChia-I Wu <olvaffe@gmail.com>
Link: http://patchwork.freedesktop.org/patch/msgid/20190813082509.29324-3-kraxel@redhat.com
parent 4100a7b8

drivers/gpu/drm/virtio/virtgpu_vq.c

+19 −6
Original line number Diff line number Diff line
@@ -252,7 +252,7 @@ void virtio_gpu_dequeue_cursor_func(struct work_struct *work) 
	wake_up(&vgdev->cursorq.ack_queue);

}



static void virtio_gpu_queue_ctrl_buffer_locked(struct virtio_gpu_device *vgdev,

static bool virtio_gpu_queue_ctrl_buffer_locked(struct virtio_gpu_device *vgdev,

						struct virtio_gpu_vbuffer *vbuf)

		__releases(&vgdev->ctrlq.qlock)

		__acquires(&vgdev->ctrlq.qlock)
@@ -260,10 +260,11 @@ static void virtio_gpu_queue_ctrl_buffer_locked(struct virtio_gpu_device *vgdev, 
	struct virtqueue *vq = vgdev->ctrlq.vq;

	struct scatterlist *sgs[3], vcmd, vout, vresp;

	int outcnt = 0, incnt = 0;

	bool notify = false;

	int ret;



	if (!vgdev->vqs_ready)

		return;

		return notify;



	sg_init_one(&vcmd, vbuf->buf, vbuf->size);

	sgs[outcnt + incnt] = &vcmd;
@@ -292,16 +293,21 @@ retry: 
		trace_virtio_gpu_cmd_queue(vq,

			(struct virtio_gpu_ctrl_hdr *)vbuf->buf);



		virtqueue_kick(vq);

		notify = virtqueue_kick_prepare(vq);

	}

	return notify;

}



static void virtio_gpu_queue_ctrl_buffer(struct virtio_gpu_device *vgdev,

					 struct virtio_gpu_vbuffer *vbuf)

{

	bool notify;



	spin_lock(&vgdev->ctrlq.qlock);

	virtio_gpu_queue_ctrl_buffer_locked(vgdev, vbuf);

	notify = virtio_gpu_queue_ctrl_buffer_locked(vgdev, vbuf);

	spin_unlock(&vgdev->ctrlq.qlock);

	if (notify)

		virtqueue_notify(vgdev->ctrlq.vq);

}



static void virtio_gpu_queue_fenced_ctrl_buffer(struct virtio_gpu_device *vgdev,
@@ -310,6 +316,7 @@ static void virtio_gpu_queue_fenced_ctrl_buffer(struct virtio_gpu_device *vgdev, 
						struct virtio_gpu_fence *fence)

{

	struct virtqueue *vq = vgdev->ctrlq.vq;

	bool notify;



again:

	spin_lock(&vgdev->ctrlq.qlock);
@@ -330,8 +337,10 @@ again: 


	if (fence)

		virtio_gpu_fence_emit(vgdev, hdr, fence);

	virtio_gpu_queue_ctrl_buffer_locked(vgdev, vbuf);

	notify = virtio_gpu_queue_ctrl_buffer_locked(vgdev, vbuf);

	spin_unlock(&vgdev->ctrlq.qlock);

	if (notify)

		virtqueue_notify(vgdev->ctrlq.vq);

}



static void virtio_gpu_queue_cursor(struct virtio_gpu_device *vgdev,
@@ -339,6 +348,7 @@ static void virtio_gpu_queue_cursor(struct virtio_gpu_device *vgdev, 
{

	struct virtqueue *vq = vgdev->cursorq.vq;

	struct scatterlist *sgs[1], ccmd;

	bool notify;

	int ret;

	int outcnt;
@@ -361,10 +371,13 @@ retry: 
		trace_virtio_gpu_cmd_queue(vq,

			(struct virtio_gpu_ctrl_hdr *)vbuf->buf);



		virtqueue_kick(vq);

		notify = virtqueue_kick_prepare(vq);

	}



	spin_unlock(&vgdev->cursorq.qlock);



	if (notify)

		virtqueue_notify(vq);

}



/* just create gem objects for userspace and long lived objects,

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