Re: [PATCH v4 07/13] drm/msm: Track "seqno" fences by idr

Akhil P Oommen
2021-11-10T15:29:04Z

On 7/28/2021 6:36 AM, Rob Clark wrote:
> From: Rob Clark <robdclark@chromium.org>
>
> Previously the (non-fd) fence returned from submit ioctl was a raw
> seqno, which is scoped to the ring. But from UABI standpoint, the
> ioctls related to seqno fences all specify a submitqueue. We can
> take advantage of that to replace the seqno fences with a cyclic idr
> handle.
>
> This is in preperation for moving to drm scheduler, at which point
> the submit ioctl will return after queuing the submit job to the
> scheduler, but before the submit is written into the ring (and
> therefore before a ring seqno has been assigned). Which means we
> need to replace the dma_fence that userspace may need to wait on
> with a scheduler fence.
>
> Signed-off-by: Rob Clark <robdclark@chromium.org>
> Acked-by: Christian König <christian.koenig@amd.com>
> ---
> drivers/gpu/drm/msm/msm_drv.c | 30 +++++++++++++++++--
> drivers/gpu/drm/msm/msm_fence.c | 42 ---------------------------
> drivers/gpu/drm/msm/msm_fence.h | 3 --
> drivers/gpu/drm/msm/msm_gem.h | 1 +
> drivers/gpu/drm/msm/msm_gem_submit.c | 23 ++++++++++++++-
> drivers/gpu/drm/msm/msm_gpu.h | 5 ++++
> drivers/gpu/drm/msm/msm_submitqueue.c | 5 ++++
> 7 files changed, 61 insertions(+), 48 deletions(-)
>
> diff --git a/drivers/gpu/drm/msm/msm_drv.c b/drivers/gpu/drm/msm/msm_drv.c
> index 9b8fa2ad0d84..1594ae39d54f 100644
> --- a/drivers/gpu/drm/msm/msm_drv.c
> +++ b/drivers/gpu/drm/msm/msm_drv.c
> @@ -911,6 +911,7 @@ static int msm_ioctl_wait_fence(struct drm_device *dev, void *data,
> ktime_t timeout = to_ktime(args->timeout);
> struct msm_gpu_submitqueue *queue;
> struct msm_gpu *gpu = priv->gpu;
> + struct dma_fence *fence;
> int ret;
>
> if (args->pad) {
> @@ -925,10 +926,35 @@ static int msm_ioctl_wait_fence(struct drm_device *dev, void *data,
> if (!queue)
> return -ENOENT;
>
> - ret = msm_wait_fence(gpu->rb[queue->prio]->fctx, args->fence, &timeout,
> - true);
> + /*
> + * Map submitqueue scoped "seqno" (which is actually an idr key)
> + * back to underlying dma-fence
> + *
> + * The fence is removed from the fence_idr when the submit is
> + * retired, so if the fence is not found it means there is nothing
> + * to wait for
> + */
> + ret = mutex_lock_interruptible(&queue->lock);
> + if (ret)
> + return ret;
> + fence = idr_find(&queue->fence_idr, args->fence);
> + if (fence)
> + fence = dma_fence_get_rcu(fence);
> + mutex_unlock(&queue->lock);
> +
> + if (!fence)
> + return 0;
>
> + ret = dma_fence_wait_timeout(fence, true, timeout_to_jiffies(&timeout));
> + if (ret == 0) {
> + ret = -ETIMEDOUT;
> + } else if (ret != -ERESTARTSYS) {
> + ret = 0;
> + }
> +
> + dma_fence_put(fence);
> msm_submitqueue_put(queue);
> +
> return ret;
> }
>
> diff --git a/drivers/gpu/drm/msm/msm_fence.c b/drivers/gpu/drm/msm/msm_fence.c
> index b92a9091a1e2..f2cece542c3f 100644
> --- a/drivers/gpu/drm/msm/msm_fence.c
> +++ b/drivers/gpu/drm/msm/msm_fence.c
> @@ -24,7 +24,6 @@ msm_fence_context_alloc(struct drm_device *dev, volatile uint32_t *fenceptr,
> strncpy(fctx->name, name, sizeof(fctx->name));
> fctx->context = dma_fence_context_alloc(1);
> fctx->fenceptr = fenceptr;
> - init_waitqueue_head(&fctx->event);
> spin_lock_init(&fctx->spinlock);
>
> return fctx;
> @@ -45,53 +44,12 @@ static inline bool fence_completed(struct msm_fence_context *fctx, uint32_t fenc
> (int32_t)(*fctx->fenceptr - fence) >= 0;
> }
>
> -/* legacy path for WAIT_FENCE ioctl: */
> -int msm_wait_fence(struct msm_fence_context *fctx, uint32_t fence,
> - ktime_t *timeout, bool interruptible)
> -{
> - int ret;
> -
> - if (fence > fctx->last_fence) {
> - DRM_ERROR_RATELIMITED("%s: waiting on invalid fence: %u (of %u)\n",
> - fctx->name, fence, fctx->last_fence);
> - return -EINVAL;

Rob, we changed this pre-existing behaviour in this patch. Now, when
userspace tries to wait on a future fence, we don't return an error.

I just want to check if this was accidental or not?

-Akhil.

> - }
> -
> - if (!timeout) {
> - /* no-wait: */
> - ret = fence_completed(fctx, fence) ? 0 : -EBUSY;
> - } else {
> - unsigned long remaining_jiffies = timeout_to_jiffies(timeout);
> -
> - if (interruptible)
> - ret = wait_event_interruptible_timeout(fctx->event,
> - fence_completed(fctx, fence),
> - remaining_jiffies);
> - else
> - ret = wait_event_timeout(fctx->event,
> - fence_completed(fctx, fence),
> - remaining_jiffies);
> -
> - if (ret == 0) {
> - DBG("timeout waiting for fence: %u (completed: %u)",
> - fence, fctx->completed_fence);
> - ret = -ETIMEDOUT;
> - } else if (ret != -ERESTARTSYS) {
> - ret = 0;
> - }
> - }
> -
> - return ret;
> -}
> -
> /* called from workqueue */
> void msm_update_fence(struct msm_fence_context *fctx, uint32_t fence)
> {
> spin_lock(&fctx->spinlock);
> fctx->completed_fence = max(fence, fctx->completed_fence);
> spin_unlock(&fctx->spinlock);
> -
> - wake_up_all(&fctx->event);
> }
>
> struct msm_fence {
> diff --git a/drivers/gpu/drm/msm/msm_fence.h b/drivers/gpu/drm/msm/msm_fence.h
> index 6ab97062ff1a..4783db528bcc 100644
> --- a/drivers/gpu/drm/msm/msm_fence.h
> +++ b/drivers/gpu/drm/msm/msm_fence.h
> @@ -49,7 +49,6 @@ struct msm_fence_context {
> */
> volatile uint32_t *fenceptr;
>
> - wait_queue_head_t event;
> spinlock_t spinlock;
> };
>
> @@ -57,8 +56,6 @@ struct msm_fence_context * msm_fence_context_alloc(struct drm_device *dev,
> volatile uint32_t *fenceptr, const char *name);
> void msm_fence_context_free(struct msm_fence_context *fctx);
>
> -int msm_wait_fence(struct msm_fence_context *fctx, uint32_t fence,
> - ktime_t *timeout, bool interruptible);
> void msm_update_fence(struct msm_fence_context *fctx, uint32_t fence);
>
> struct dma_fence * msm_fence_alloc(struct msm_fence_context *fctx);
> diff --git a/drivers/gpu/drm/msm/msm_gem.h b/drivers/gpu/drm/msm/msm_gem.h
> index da3af702a6c8..e0579abda5b9 100644
> --- a/drivers/gpu/drm/msm/msm_gem.h
> +++ b/drivers/gpu/drm/msm/msm_gem.h
> @@ -320,6 +320,7 @@ struct msm_gem_submit {
> struct ww_acquire_ctx ticket;
> uint32_t seqno; /* Sequence number of the submit on the ring */
> struct dma_fence *fence;
> + int fence_id; /* key into queue->fence_idr */
> struct msm_gpu_submitqueue *queue;
> struct pid *pid; /* submitting process */
> bool fault_dumped; /* Limit devcoredump dumping to one per submit */
> diff --git a/drivers/gpu/drm/msm/msm_gem_submit.c b/drivers/gpu/drm/msm/msm_gem_submit.c
> index 4f02fa3c78f9..f6f595aae2c5 100644
> --- a/drivers/gpu/drm/msm/msm_gem_submit.c
> +++ b/drivers/gpu/drm/msm/msm_gem_submit.c
> @@ -68,7 +68,14 @@ void __msm_gem_submit_destroy(struct kref *kref)
> container_of(kref, struct msm_gem_submit, ref);
> unsigned i;
>
> + if (submit->fence_id) {
> + mutex_lock(&submit->queue->lock);
> + idr_remove(&submit->queue->fence_idr, submit->fence_id);
> + mutex_unlock(&submit->queue->lock);
> + }
> +
> dma_fence_put(submit->fence);
> +
> put_pid(submit->pid);
> msm_submitqueue_put(submit->queue);
>
> @@ -872,6 +879,20 @@ int msm_ioctl_gem_submit(struct drm_device *dev, void *data,
> goto out;
> }
>
> + /*
> + * Allocate an id which can be used by WAIT_FENCE ioctl to map back
> + * to the underlying fence.
> + */
> + mutex_lock(&queue->lock);
> + submit->fence_id = idr_alloc_cyclic(&queue->fence_idr,
> + submit->fence, 0, INT_MAX, GFP_KERNEL);
> + mutex_unlock(&queue->lock);
> + if (submit->fence_id < 0) {
> + ret = submit->fence_id = 0;
> + submit->fence_id = 0;
> + goto out;
> + }
> +
> if (args->flags & MSM_SUBMIT_FENCE_FD_OUT) {
> struct sync_file *sync_file = sync_file_create(submit->fence);
> if (!sync_file) {
> @@ -886,7 +907,7 @@ int msm_ioctl_gem_submit(struct drm_device *dev, void *data,
>
> msm_gpu_submit(gpu, submit);
>
> - args->fence = submit->fence->seqno;
> + args->fence = submit->fence_id;
>
> msm_reset_syncobjs(syncobjs_to_reset, args->nr_in_syncobjs);
> msm_process_post_deps(post_deps, args->nr_out_syncobjs,
> diff --git a/drivers/gpu/drm/msm/msm_gpu.h b/drivers/gpu/drm/msm/msm_gpu.h
> index 96efcb31e502..579627252540 100644
> --- a/drivers/gpu/drm/msm/msm_gpu.h
> +++ b/drivers/gpu/drm/msm/msm_gpu.h
> @@ -263,6 +263,9 @@ struct msm_gpu_perfcntr {
> * which set of pgtables do submits jobs associated with the
> * submitqueue use)
> * @node: node in the context's list of submitqueues
> + * @fence_idr: maps fence-id to dma_fence for userspace visible fence
> + * seqno, protected by submitqueue lock
> + * @lock: submitqueue lock
> * @ref: reference count
> */
> struct msm_gpu_submitqueue {
> @@ -272,6 +275,8 @@ struct msm_gpu_submitqueue {
> int faults;
> struct msm_file_private *ctx;
> struct list_head node;
> + struct idr fence_idr;
> + struct mutex lock;
> struct kref ref;
> };
>
> diff --git a/drivers/gpu/drm/msm/msm_submitqueue.c b/drivers/gpu/drm/msm/msm_submitqueue.c
> index 9e9fec61d629..66f8d0fb38b0 100644
> --- a/drivers/gpu/drm/msm/msm_submitqueue.c
> +++ b/drivers/gpu/drm/msm/msm_submitqueue.c
> @@ -12,6 +12,8 @@ void msm_submitqueue_destroy(struct kref *kref)
> struct msm_gpu_submitqueue *queue = container_of(kref,
> struct msm_gpu_submitqueue, ref);
>
> + idr_destroy(&queue->fence_idr);
> +
> msm_file_private_put(queue->ctx);
>
> kfree(queue);
> @@ -89,6 +91,9 @@ int msm_submitqueue_create(struct drm_device *drm, struct msm_file_private *ctx,
> if (id)
> *id = queue->id;
>
> + idr_init(&queue->fence_idr);
> + mutex_init(&queue->lock);
> +
> list_add_tail(&queue->node, &ctx->submitqueues);
>
> write_unlock(&ctx->queuelock);
>