[Intel-gfx] [PATCH 2/2] drm/i915: Record the tail at each request and use it to estimate the head
Chris Wilson
chris at chris-wilson.co.uk
Wed Feb 8 14:34:14 CET 2012
By recording the location of every request in the ringbuffer, we know
that in order to retire the request the GPU must have finished reading
it and so the GPU head is now beyond the tail of the request. We can
therefore provide a conservative estimate of where the GPU is reading
from in order to avoid having to read back the ring buffer registers
when polling for space upon starting a new write into the ringbuffer.
A secondary effect is that this allows us to convert
intel_ring_buffer_wait() to use i915_wait_request() and so consolidate
upon the single function to handle the complicated task of waiting upon
the GPU. A necessary precaution is that we need to make that wait
uninterruptible to match the existing conditions as all the callers of
intel_ring_begin() have not been audited to handle ERESTARTSYS
correctly.
Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
---
drivers/gpu/drm/i915/i915_drv.h | 5 ++
drivers/gpu/drm/i915/i915_gem.c | 9 ++++-
drivers/gpu/drm/i915/intel_ringbuffer.c | 70 +++++++++++++++++++++++++++++++
drivers/gpu/drm/i915/intel_ringbuffer.h | 15 +++++++
4 files changed, 98 insertions(+), 1 deletions(-)
diff --git a/drivers/gpu/drm/i915/i915_drv.h b/drivers/gpu/drm/i915/i915_drv.h
index 4ee0793..e8e1b85 100644
--- a/drivers/gpu/drm/i915/i915_drv.h
+++ b/drivers/gpu/drm/i915/i915_drv.h
@@ -945,6 +945,9 @@ struct drm_i915_gem_request {
/** GEM sequence number associated with this request. */
uint32_t seqno;
+ /** Postion in the ringbuffer of the end of the request */
+ u32 tail;
+
/** Time at which this request was emitted, in jiffies. */
unsigned long emitted_jiffies;
@@ -1234,6 +1237,8 @@ i915_gem_object_unpin_fence(struct drm_i915_gem_object *obj)
}
void i915_gem_retire_requests(struct drm_device *dev);
+void i915_gem_retire_requests_ring(struct intel_ring_buffer *ring);
+
void i915_gem_reset(struct drm_device *dev);
void i915_gem_clflush_object(struct drm_i915_gem_object *obj);
int __must_check i915_gem_object_set_domain(struct drm_i915_gem_object *obj,
diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c
index 51390b0..4de9e4e 100644
--- a/drivers/gpu/drm/i915/i915_gem.c
+++ b/drivers/gpu/drm/i915/i915_gem.c
@@ -1798,6 +1798,7 @@ i915_add_request(struct intel_ring_buffer *ring,
request->seqno = seqno;
request->ring = ring;
+ request->tail = intel_ring_get_tail(ring);
request->emitted_jiffies = jiffies;
was_empty = list_empty(&ring->request_list);
list_add_tail(&request->list, &ring->request_list);
@@ -1934,7 +1935,7 @@ void i915_gem_reset(struct drm_device *dev)
/**
* This function clears the request list as sequence numbers are passed.
*/
-static void
+void
i915_gem_retire_requests_ring(struct intel_ring_buffer *ring)
{
uint32_t seqno;
@@ -1962,6 +1963,12 @@ i915_gem_retire_requests_ring(struct intel_ring_buffer *ring)
break;
trace_i915_gem_request_retire(ring, request->seqno);
+ /* We know the GPU must have read the request to have
+ * sent us the seqno + interrupt, so use the position
+ * of tail of the request to update the last known position
+ * of the GPU head.
+ */
+ ring->last_retired_head = request->tail;
list_del(&request->list);
i915_gem_request_remove_from_client(request);
diff --git a/drivers/gpu/drm/i915/intel_ringbuffer.c b/drivers/gpu/drm/i915/intel_ringbuffer.c
index 620b2ed..f539235 100644
--- a/drivers/gpu/drm/i915/intel_ringbuffer.c
+++ b/drivers/gpu/drm/i915/intel_ringbuffer.c
@@ -533,6 +533,7 @@ pc_render_add_request(struct intel_ring_buffer *ring,
PIPE_CONTROL_FLUSH(ring, scratch_addr);
scratch_addr += 128;
PIPE_CONTROL_FLUSH(ring, scratch_addr);
+
intel_ring_emit(ring, GFX_OP_PIPE_CONTROL(4) | PIPE_CONTROL_QW_WRITE |
PIPE_CONTROL_WRITE_FLUSH |
PIPE_CONTROL_TEXTURE_CACHE_INVALIDATE |
@@ -1054,11 +1055,80 @@ static int intel_wrap_ring_buffer(struct intel_ring_buffer *ring)
return 0;
}
+static int intel_ring_wait_seqno(struct intel_ring_buffer *ring, u32 seqno)
+{
+ struct drm_i915_private *dev_priv = ring->dev->dev_private;
+ bool was_interruptible;
+ int ret;
+
+ /* XXX As we have not yet audited all the paths to check that
+ * they are ready for ERESTARTSYS from intel_ring_begin, do not
+ * allow us to be interruptible by a signal.
+ */
+ was_interruptible = dev_priv->mm.interruptible;
+ dev_priv->mm.interruptible = false;
+
+ ret = i915_wait_request(ring, seqno);
+
+ dev_priv->mm.interruptible = was_interruptible;
+
+ return ret;
+}
+
+static int intel_ring_wait_request(struct intel_ring_buffer *ring, int n)
+{
+ struct drm_i915_gem_request *request;
+ u32 seqno = 0;
+ int ret;
+
+ if (ring->last_retired_head != -1) {
+ ring->head = ring->last_retired_head;
+ ring->last_retired_head = -1;
+ ring->space = ring_space(ring);
+ if (ring->space >= n)
+ return 0;
+ }
+
+ list_for_each_entry(request, &ring->request_list, list) {
+ int space = request->tail - (ring->tail + 8);
+ if (space < 0)
+ space += ring->size;
+ if (space >= n) {
+ seqno = request->seqno;
+ break;
+ }
+ request->tail = -1;
+ }
+
+ if (seqno == 0)
+ return -ENOSPC;
+
+ ret = intel_ring_wait_seqno(ring, seqno);
+ if (ret)
+ return ret;
+
+ if (WARN_ON(ring->last_retired_head == -1))
+ return -ENOSPC;
+
+ ring->head = ring->last_retired_head;
+ ring->last_retired_head = -1;
+ ring->space = ring_space(ring);
+ if (WARN_ON(ring->space < n))
+ return -ENOSPC;
+
+ return 0;
+}
+
int intel_wait_ring_buffer(struct intel_ring_buffer *ring, int n)
{
struct drm_device *dev = ring->dev;
struct drm_i915_private *dev_priv = dev->dev_private;
unsigned long end;
+ int ret;
+
+ ret = intel_ring_wait_request(ring, n);
+ if (ret != -ENOSPC)
+ return ret;
trace_i915_ring_wait_begin(ring);
if (drm_core_check_feature(dev, DRIVER_GEM))
diff --git a/drivers/gpu/drm/i915/intel_ringbuffer.h b/drivers/gpu/drm/i915/intel_ringbuffer.h
index 4c5338c..855233b 100644
--- a/drivers/gpu/drm/i915/intel_ringbuffer.h
+++ b/drivers/gpu/drm/i915/intel_ringbuffer.h
@@ -46,6 +46,16 @@ struct intel_ring_buffer {
int effective_size;
struct intel_hw_status_page status_page;
+ /** We track the position of the requests in the ring buffer, and
+ * when each is retired we increment last_retired_head as the GPU
+ * must have finished processing the request and so we know we
+ * can advance the ringbuffer up to that position.
+ *
+ * last_retired_head is set to -1 after the value is consumed so
+ * we can detect new retirements.
+ */
+ u32 last_retired_head;
+
spinlock_t irq_lock;
u32 irq_refcount;
u32 irq_mask;
@@ -191,6 +201,11 @@ int intel_init_blt_ring_buffer(struct drm_device *dev);
u32 intel_ring_get_active_head(struct intel_ring_buffer *ring);
void intel_ring_setup_status_page(struct intel_ring_buffer *ring);
+static inline u32 intel_ring_get_tail(struct intel_ring_buffer *ring)
+{
+ return ring->tail;
+}
+
static inline void i915_trace_irq_get(struct intel_ring_buffer *ring, u32 seqno)
{
if (ring->trace_irq_seqno == 0 && ring->irq_get(ring))
--
1.7.9
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