On Tue, Aug 13, 2019 at 1:25 AM Gerd Hoffmann <kraxel@xxxxxxxxxx> wrote:
>
> 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: Chia-I Wu <olvaffe@xxxxxxxxx>
> Signed-off-by: Gerd Hoffmann <kraxel@xxxxxxxxxx>
Series is
Reviewed-by: Chia-I Wu <olvaffe@xxxxxxxxx>
> ---
> drivers/gpu/drm/virtio/virtgpu_vq.c | 25 +++++++++++++++++++------
> 1 file changed, 19 insertions(+), 6 deletions(-)
>
> diff --git a/drivers/gpu/drm/virtio/virtgpu_vq.c b/drivers/gpu/drm/virtio/virtgpu_vq.c
> index ca91e83ffaef..e41c96143342 100644
> --- a/drivers/gpu/drm/virtio/virtgpu_vq.c
> +++ b/drivers/gpu/drm/virtio/virtgpu_vq.c
> @@ -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 @@ static void virtio_gpu_queue_ctrl_buffer_locked(struct virtio_gpu_device *vgdev,
> 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 @@ static void virtio_gpu_queue_fenced_ctrl_buffer(struct virtio_gpu_device *vgdev,
>
> 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 @@ static void virtio_gpu_queue_cursor(struct virtio_gpu_device *vgdev,
> 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,
> --
> 2.18.1
>
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