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Message-ID: <CAPaKu7QP=A2kV_kqcT20Pmc831HviaBJN1RpOFoa=V1g6SmE_g@mail.gmail.com>
Date: Wed, 3 Jul 2019 11:49:27 -0700
From: Chia-I Wu <olvaffe@...il.com>
To: Gerd Hoffmann <kraxel@...hat.com>
Cc: ML dri-devel <dri-devel@...ts.freedesktop.org>,
Gurchetan Singh <gurchetansingh@...omium.org>,
David Airlie <airlied@...ux.ie>,
Daniel Vetter <daniel@...ll.ch>,
"open list:VIRTIO GPU DRIVER"
<virtualization@...ts.linux-foundation.org>,
open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v6 08/18] drm/virtio: rework virtio_gpu_execbuffer_ioctl fencing
On Tue, Jul 2, 2019 at 7:19 AM Gerd Hoffmann <kraxel@...hat.com> wrote:
>
> Rework fencing workflow, starting with virtio_gpu_execbuffer_ioctl.
> Stop using ttm helpers, use the virtio_gpu_array_* helpers (which work
> on the reservation objects directly) instead.
>
> New workflow:
>
> (1) All gem objects needed by a command are added to a
> virtio_gpu_object_array.
> (2) All reservation objects will be locked (virtio_gpu_array_lock_resv).
> (3) virtio_gpu_fence_emit() completes fence initialization.
> (4) fence gets added to the objects, reservation objects are unlocked
> (virtio_gpu_array_add_fence, virtio_gpu_array_unlock_resv).
> (5) virtio command is submitted to the host.
> (6) The completion callback (virtio_gpu_dequeue_ctrl_func)
> will drop object references and free virtio_gpu_object_array.
>
> v6: rewrite most of the patch.
>
> Signed-off-by: Gerd Hoffmann <kraxel@...hat.com>
> ---
> drivers/gpu/drm/virtio/virtgpu_drv.h | 6 ++-
> drivers/gpu/drm/virtio/virtgpu_ioctl.c | 56 +++++++++-----------------
> drivers/gpu/drm/virtio/virtgpu_vq.c | 21 +++++++---
> 3 files changed, 38 insertions(+), 45 deletions(-)
>
> diff --git a/drivers/gpu/drm/virtio/virtgpu_drv.h b/drivers/gpu/drm/virtio/virtgpu_drv.h
> index abb078a5dedf..98511d1dfff2 100644
> --- a/drivers/gpu/drm/virtio/virtgpu_drv.h
> +++ b/drivers/gpu/drm/virtio/virtgpu_drv.h
> @@ -121,9 +121,9 @@ struct virtio_gpu_vbuffer {
>
> char *resp_buf;
> int resp_size;
> -
> virtio_gpu_resp_cb resp_cb;
>
> + struct virtio_gpu_object_array *objs;
> struct list_head list;
> };
>
> @@ -318,7 +318,9 @@ void virtio_gpu_cmd_context_detach_resource(struct virtio_gpu_device *vgdev,
> uint32_t resource_id);
> void virtio_gpu_cmd_submit(struct virtio_gpu_device *vgdev,
> void *data, uint32_t data_size,
> - uint32_t ctx_id, struct virtio_gpu_fence *fence);
> + uint32_t ctx_id,
> + struct virtio_gpu_object_array *objs,
> + struct virtio_gpu_fence *fence);
> void virtio_gpu_cmd_transfer_from_host_3d(struct virtio_gpu_device *vgdev,
> uint32_t resource_id, uint32_t ctx_id,
> uint64_t offset, uint32_t level,
> diff --git a/drivers/gpu/drm/virtio/virtgpu_ioctl.c b/drivers/gpu/drm/virtio/virtgpu_ioctl.c
> index 0caff3fa623e..9735d7e5899b 100644
> --- a/drivers/gpu/drm/virtio/virtgpu_ioctl.c
> +++ b/drivers/gpu/drm/virtio/virtgpu_ioctl.c
> @@ -105,16 +105,11 @@ static int virtio_gpu_execbuffer_ioctl(struct drm_device *dev, void *data,
> struct drm_virtgpu_execbuffer *exbuf = data;
> struct virtio_gpu_device *vgdev = dev->dev_private;
> struct virtio_gpu_fpriv *vfpriv = drm_file->driver_priv;
> - struct drm_gem_object *gobj;
> struct virtio_gpu_fence *out_fence;
> - struct virtio_gpu_object *qobj;
> int ret;
> uint32_t *bo_handles = NULL;
> void __user *user_bo_handles = NULL;
> - struct list_head validate_list;
> - struct ttm_validate_buffer *buflist = NULL;
> - int i;
> - struct ww_acquire_ctx ticket;
> + struct virtio_gpu_object_array *buflist = NULL;
> struct sync_file *sync_file;
> int in_fence_fd = exbuf->fence_fd;
> int out_fence_fd = -1;
> @@ -155,15 +150,10 @@ static int virtio_gpu_execbuffer_ioctl(struct drm_device *dev, void *data,
> return out_fence_fd;
> }
>
> - INIT_LIST_HEAD(&validate_list);
> if (exbuf->num_bo_handles) {
> -
> bo_handles = kvmalloc_array(exbuf->num_bo_handles,
> - sizeof(uint32_t), GFP_KERNEL);
> - buflist = kvmalloc_array(exbuf->num_bo_handles,
> - sizeof(struct ttm_validate_buffer),
> - GFP_KERNEL | __GFP_ZERO);
> - if (!bo_handles || !buflist) {
> + sizeof(uint32_t), GFP_KERNEL);
> + if (!bo_handles) {
> ret = -ENOMEM;
> goto out_unused_fd;
> }
> @@ -175,25 +165,21 @@ static int virtio_gpu_execbuffer_ioctl(struct drm_device *dev, void *data,
> goto out_unused_fd;
> }
>
> - for (i = 0; i < exbuf->num_bo_handles; i++) {
> - gobj = drm_gem_object_lookup(drm_file, bo_handles[i]);
> - if (!gobj) {
> - ret = -ENOENT;
> - goto out_unused_fd;
> - }
> -
> - qobj = gem_to_virtio_gpu_obj(gobj);
> - buflist[i].bo = &qobj->tbo;
> -
> - list_add(&buflist[i].head, &validate_list);
> + buflist = virtio_gpu_array_from_handles(drm_file, bo_handles,
> + exbuf->num_bo_handles);
> + if (!buflist) {
> + ret = -ENOENT;
> + goto out_unused_fd;
> }
> kvfree(bo_handles);
> bo_handles = NULL;
> }
>
> - ret = virtio_gpu_object_list_validate(&ticket, &validate_list);
> - if (ret)
> - goto out_free;
> + if (buflist) {
> + ret = virtio_gpu_array_lock_resv(buflist);
> + if (ret)
> + goto out_unused_fd;
> + }
>
> buf = memdup_user(u64_to_user_ptr(exbuf->command), exbuf->size);
> if (IS_ERR(buf)) {
> @@ -220,24 +206,18 @@ static int virtio_gpu_execbuffer_ioctl(struct drm_device *dev, void *data,
> }
>
> virtio_gpu_cmd_submit(vgdev, buf, exbuf->size,
> - vfpriv->ctx_id, out_fence);
> -
> - ttm_eu_fence_buffer_objects(&ticket, &validate_list, &out_fence->f);
> -
> - /* fence the command bo */
> - virtio_gpu_unref_list(&validate_list);
> - kvfree(buflist);
> + vfpriv->ctx_id, buflist, out_fence);
> return 0;
>
> out_memdup:
> kfree(buf);
> out_unresv:
> - ttm_eu_backoff_reservation(&ticket, &validate_list);
> -out_free:
> - virtio_gpu_unref_list(&validate_list);
> + if (buflist)
> + virtio_gpu_array_unlock_resv(buflist);
> out_unused_fd:
> kvfree(bo_handles);
> - kvfree(buflist);
> + if (buflist)
> + virtio_gpu_array_put_free(buflist);
>
> if (out_fence_fd >= 0)
> put_unused_fd(out_fence_fd);
> diff --git a/drivers/gpu/drm/virtio/virtgpu_vq.c b/drivers/gpu/drm/virtio/virtgpu_vq.c
> index 6c1a90717535..dbe329801e84 100644
> --- a/drivers/gpu/drm/virtio/virtgpu_vq.c
> +++ b/drivers/gpu/drm/virtio/virtgpu_vq.c
> @@ -191,7 +191,7 @@ void virtio_gpu_dequeue_ctrl_func(struct work_struct *work)
> } while (!virtqueue_enable_cb(vgdev->ctrlq.vq));
> spin_unlock(&vgdev->ctrlq.qlock);
>
> - list_for_each_entry_safe(entry, tmp, &reclaim_list, list) {
> + list_for_each_entry(entry, &reclaim_list, list) {
> resp = (struct virtio_gpu_ctrl_hdr *)entry->resp_buf;
>
> trace_virtio_gpu_cmd_response(vgdev->ctrlq.vq, resp);
> @@ -218,14 +218,18 @@ void virtio_gpu_dequeue_ctrl_func(struct work_struct *work)
> }
> if (entry->resp_cb)
> entry->resp_cb(vgdev, entry);
> -
> - list_del(&entry->list);
> - free_vbuf(vgdev, entry);
> }
> wake_up(&vgdev->ctrlq.ack_queue);
>
> if (fence_id)
> virtio_gpu_fence_event_process(vgdev, fence_id);
> +
> + list_for_each_entry_safe(entry, tmp, &reclaim_list, list) {
> + if (entry->objs)
> + virtio_gpu_array_put_free(entry->objs);
> + list_del(&entry->list);
> + free_vbuf(vgdev, entry);
> + }
> }
>
> void virtio_gpu_dequeue_cursor_func(struct work_struct *work)
> @@ -337,6 +341,10 @@ static int virtio_gpu_queue_fenced_ctrl_buffer(struct virtio_gpu_device *vgdev,
>
> if (fence)
> virtio_gpu_fence_emit(vgdev, hdr, fence);
> + if (vbuf->objs) {
> + virtio_gpu_array_add_fence(vbuf->objs, &fence->f);
> + virtio_gpu_array_unlock_resv(vbuf->objs);
> + }
This is with the spinlock held. Maybe we should move the
virtio_gpu_array_unlock_resv call out of the critical section.
I am actually more concerned about virtio_gpu_array_add_fence, but it
is also harder to move. Should we add a kref to the object array?
This bothers me because I recently ran into a CPU-bound game with very
bad lock contention here.
> rc = virtio_gpu_queue_ctrl_buffer_locked(vgdev, vbuf);
> spin_unlock(&vgdev->ctrlq.qlock);
> return rc;
> @@ -939,7 +947,9 @@ void virtio_gpu_cmd_transfer_from_host_3d(struct virtio_gpu_device *vgdev,
>
> void virtio_gpu_cmd_submit(struct virtio_gpu_device *vgdev,
> void *data, uint32_t data_size,
> - uint32_t ctx_id, struct virtio_gpu_fence *fence)
> + uint32_t ctx_id,
> + struct virtio_gpu_object_array *objs,
> + struct virtio_gpu_fence *fence)
> {
> struct virtio_gpu_cmd_submit *cmd_p;
> struct virtio_gpu_vbuffer *vbuf;
> @@ -949,6 +959,7 @@ void virtio_gpu_cmd_submit(struct virtio_gpu_device *vgdev,
>
> vbuf->data_buf = data;
> vbuf->data_size = data_size;
> + vbuf->objs = objs;
>
> cmd_p->hdr.type = cpu_to_le32(VIRTIO_GPU_CMD_SUBMIT_3D);
> cmd_p->hdr.ctx_id = cpu_to_le32(ctx_id);
> --
> 2.18.1
>
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