[RFC 5/9] drm/i915: Add per context timelines to fence object

John.C.Harrison
2015-07-17T14:31:38Z

From: John Harrison <John.C.Harrison@Intel.com>

The fence object used inside the request structure requires a sequence number.
Although this is not used by the i915 driver itself, it could potentially be
used by non-i915 code if the fence is passed outside of the driver. This is the
intention as it allows external kernel drivers and user applications to wait on
batch buffer completion asynchronously via the dma-buff fence API.

To ensure that such external users are not confused by strange things happening
with the seqno, this patch adds in a per context timeline that can provide a
guaranteed in-order seqno value for the fence. This is safe because the
scheduler will not re-order batch buffers within a context - they are considered
to be mutually dependent.

[new patch in series]

For: VIZ-5190
Signed-off-by: John Harrison <John.C.Harrison@Intel.com>
---
drivers/gpu/drm/i915/i915_drv.h | 25 ++++++++----
drivers/gpu/drm/i915/i915_gem.c | 69 ++++++++++++++++++++++++++++++---
drivers/gpu/drm/i915/i915_gem_context.c | 15 ++++++-
drivers/gpu/drm/i915/intel_lrc.c | 8 ++++
drivers/gpu/drm/i915/intel_ringbuffer.h | 1 -
5 files changed, 103 insertions(+), 15 deletions(-)

diff --git a/drivers/gpu/drm/i915/i915_drv.h b/drivers/gpu/drm/i915/i915_drv.h
index 0c7df46..88a4746 100644
--- a/drivers/gpu/drm/i915/i915_drv.h
+++ b/drivers/gpu/drm/i915/i915_drv.h
@@ -840,6 +840,15 @@ struct i915_ctx_hang_stats {
bool banned;
};

+struct i915_fence_timeline {
+ unsigned fence_context;
+ uint32_t context;
+ uint32_t next;
+
+ struct intel_context *ctx;
+ struct intel_engine_cs *ring;
+};
+
/* This must match up with the value previously used for execbuf2.rsvd1. */
#define DEFAULT_CONTEXT_HANDLE 0

@@ -885,6 +894,7 @@ struct intel_context {
struct drm_i915_gem_object *state;
struct intel_ringbuffer *ringbuf;
int pin_count;
+ struct i915_fence_timeline fence_timeline;
} engine[I915_NUM_RINGS];

struct list_head link;
@@ -2153,13 +2163,10 @@ void i915_gem_track_fb(struct drm_i915_gem_object *old,
struct drm_i915_gem_request {
/**
* Underlying object for implementing the signal/wait stuff.
- * NB: Never call fence_later() or return this fence object to user
- * land! Due to lazy allocation, scheduler re-ordering, pre-emption,
- * etc., there is no guarantee at all about the validity or
- * sequentiality of the fence's seqno! It is also unsafe to let
- * anything outside of the i915 driver get hold of the fence object
- * as the clean up when decrementing the reference count requires
- * holding the driver mutex lock.
+ * NB: Never return this fence object to user land! It is unsafe to
+ * let anything outside of the i915 driver get hold of the fence
+ * object as the clean up when decrementing the reference count
+ * requires holding the driver mutex lock.
*/
struct fence fence;

@@ -2239,6 +2246,10 @@ int i915_gem_request_alloc(struct intel_engine_cs *ring,
struct drm_i915_gem_request **req_out);
void i915_gem_request_cancel(struct drm_i915_gem_request *req);

+int i915_create_fence_timeline(struct drm_device *dev,
+ struct intel_context *ctx,
+ struct intel_engine_cs *ring);
+
static inline bool i915_gem_request_completed(struct drm_i915_gem_request *req)
{
return fence_is_signaled(&req->fence);
diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c
index 3970250..af79716 100644
--- a/drivers/gpu/drm/i915/i915_gem.c
+++ b/drivers/gpu/drm/i915/i915_gem.c
@@ -2671,6 +2671,25 @@ static bool i915_gem_request_is_completed(struct fence *req_fence)
return i915_seqno_passed(seqno, req->seqno);
}

+static void i915_fence_timeline_value_str(struct fence *fence, char *str, int size)
+{
+ struct drm_i915_gem_request *req;
+
+ req = container_of(fence, typeof(*req), fence);
+
+ /* Last signalled timeline value ??? */
+ snprintf(str, size, "? [%d]"/*, tl->value*/, req->ring->get_seqno(req->ring, true));
+}
+
+static void i915_fence_value_str(struct fence *fence, char *str, int size)
+{
+ struct drm_i915_gem_request *req;
+
+ req = container_of(fence, typeof(*req), fence);
+
+ snprintf(str, size, "%d [%d]", req->fence.seqno, req->seqno);
+}
+
static const struct fence_ops i915_gem_request_fops = {
.get_driver_name = i915_gem_request_get_driver_name,
.get_timeline_name = i915_gem_request_get_timeline_name,
@@ -2678,8 +2697,48 @@ static const struct fence_ops i915_gem_request_fops = {
.signaled = i915_gem_request_is_completed,
.wait = fence_default_wait,
.release = i915_gem_request_free,
+ .fence_value_str = i915_fence_value_str,
+ .timeline_value_str = i915_fence_timeline_value_str,
};

+int i915_create_fence_timeline(struct drm_device *dev,
+ struct intel_context *ctx,
+ struct intel_engine_cs *ring)
+{
+ struct i915_fence_timeline *timeline;
+
+ timeline = &ctx->engine[ring->id].fence_timeline;
+
+ if (timeline->ring)
+ return 0;
+
+ timeline->fence_context = fence_context_alloc(1);
+
+ /*
+ * Start the timeline from seqno 0 as this is a special value
+ * that is reserved for invalid sync points.
+ */
+ timeline->next = 1;
+ timeline->ctx = ctx;
+ timeline->ring = ring;
+
+ return 0;
+}
+
+static uint32_t i915_fence_timeline_get_next_seqno(struct i915_fence_timeline *timeline)
+{
+ uint32_t seqno;
+
+ seqno = timeline->next;
+
+ /* Reserve zero for invalid */
+ if (++timeline->next == 0 ) {
+ timeline->next = 1;
+ }
+
+ return seqno;
+}
+
int i915_gem_request_alloc(struct intel_engine_cs *ring,
struct intel_context *ctx,
struct drm_i915_gem_request **req_out)
@@ -2715,7 +2774,9 @@ int i915_gem_request_alloc(struct intel_engine_cs *ring,
goto err;
}

- fence_init(&req->fence, &i915_gem_request_fops, &ring->fence_lock, ring->fence_context, req->seqno);
+ fence_init(&req->fence, &i915_gem_request_fops, &ring->fence_lock,
+ ctx->engine[ring->id].fence_timeline.fence_context,
+ i915_fence_timeline_get_next_seqno(&ctx->engine[ring->id].fence_timeline));

/*
* Reserve space in the ring buffer for all the commands required to
@@ -5065,7 +5126,7 @@ i915_gem_init_hw(struct drm_device *dev)
{
struct drm_i915_private *dev_priv = dev->dev_private;
struct intel_engine_cs *ring;
- int ret, i, j, fence_base;
+ int ret, i, j;

if (INTEL_INFO(dev)->gen < 6 && !intel_enable_gtt())
return -EIO;
@@ -5117,16 +5178,12 @@ i915_gem_init_hw(struct drm_device *dev)
goto out;
}

- fence_base = fence_context_alloc(I915_NUM_RINGS);
-
/* Now it is safe to go back round and do everything else: */
for_each_ring(ring, dev_priv, i) {
struct drm_i915_gem_request *req;

WARN_ON(!ring->default_context);

- ring->fence_context = fence_base + i;
-
ret = i915_gem_request_alloc(ring, ring->default_context, &req);
if (ret) {
i915_gem_cleanup_ringbuffer(dev);
diff --git a/drivers/gpu/drm/i915/i915_gem_context.c b/drivers/gpu/drm/i915/i915_gem_context.c
index b77a8f7..7eb8694 100644
--- a/drivers/gpu/drm/i915/i915_gem_context.c
+++ b/drivers/gpu/drm/i915/i915_gem_context.c
@@ -242,7 +242,7 @@ i915_gem_create_context(struct drm_device *dev,
{
const bool is_global_default_ctx = file_priv == NULL;
struct intel_context *ctx;
- int ret = 0;
+ int i, ret = 0;

BUG_ON(!mutex_is_locked(&dev->struct_mutex));

@@ -250,6 +250,19 @@ i915_gem_create_context(struct drm_device *dev,
if (IS_ERR(ctx))
return ctx;

+ if (!i915.enable_execlists) {
+ struct intel_engine_cs *ring;
+
+ /* Create a per context timeline for fences */
+ for_each_ring(ring, to_i915(dev), i) {
+ ret = i915_create_fence_timeline(dev, ctx, ring);
+ if (ret) {
+ DRM_ERROR("Fence timeline creation failed for legacy %s: %p\n", ring->name, ctx);
+ goto err_destroy;
+ }
+ }
+ }
+
if (is_global_default_ctx && ctx->legacy_hw_ctx.rcs_state) {
/* We may need to do things with the shrinker which
* require us to immediately switch back to the default
diff --git a/drivers/gpu/drm/i915/intel_lrc.c b/drivers/gpu/drm/i915/intel_lrc.c
index ee4aecd..8f255de 100644
--- a/drivers/gpu/drm/i915/intel_lrc.c
+++ b/drivers/gpu/drm/i915/intel_lrc.c
@@ -2376,6 +2376,14 @@ int intel_lr_context_deferred_create(struct intel_context *ctx,
goto error;
}

+ /* Create a per context timeline for fences */
+ ret = i915_create_fence_timeline(dev, ctx, ring);
+ if (ret) {
+ DRM_ERROR("Fence timeline creation failed for ring %s, ctx %p\n",
+ ring->name, ctx);
+ goto error;
+ }
+
ctx->engine[ring->id].ringbuf = ringbuf;
ctx->engine[ring->id].state = ctx_obj;

diff --git a/drivers/gpu/drm/i915/intel_ringbuffer.h b/drivers/gpu/drm/i915/intel_ringbuffer.h
index a4b0545..e2eebc0 100644
--- a/drivers/gpu/drm/i915/intel_ringbuffer.h
+++ b/drivers/gpu/drm/i915/intel_ringbuffer.h
@@ -347,7 +347,6 @@ struct intel_engine_cs {
*/
u32 (*get_cmd_length_mask)(u32 cmd_header);

- unsigned fence_context;
spinlock_t fence_lock;
};

--
1.9.1