[PATCH 06/11] drm/i915: Introduce a preempt context
Chris Wilson
chris at chris-wilson.co.uk
Thu Sep 28 11:27:37 UTC 2017
Add another perma-pinned context for using for preemption at any time.
We cannot just reuse the existing kernel context, as first and foremost
we need to ensure that we can preempt the kernel context itself, so
require a distinct context id. Similar to the kernel context, we may
want to interrupt execution and switch to the preempt context at any
time, and so it needs to be permanently pinned and available.
To compensate for yet another permanent allocation, we shrink the
existing context and the new context by reducing their ringbuffer to the
minimum.
v2: Assert that we never allocate a request from the preemption context.
v3: Limit perma-pin to engines that may preempt.
Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
Reviewed-by: Michał Winiarski <michal.winiarski at intel.com>
---
drivers/gpu/drm/i915/i915_drv.h | 4 +++-
drivers/gpu/drm/i915/i915_gem_context.c | 42 ++++++++++++++++++++++++++-------
drivers/gpu/drm/i915/i915_gem_request.c | 7 ++++++
drivers/gpu/drm/i915/intel_engine_cs.c | 22 +++++++++++++++--
4 files changed, 64 insertions(+), 11 deletions(-)
diff --git a/drivers/gpu/drm/i915/i915_drv.h b/drivers/gpu/drm/i915/i915_drv.h
index b7cba89080ed..b6794b103255 100644
--- a/drivers/gpu/drm/i915/i915_drv.h
+++ b/drivers/gpu/drm/i915/i915_drv.h
@@ -783,6 +783,7 @@ struct intel_csr {
func(has_l3_dpf); \
func(has_llc); \
func(has_logical_ring_contexts); \
+ func(has_logical_ring_preemption); \
func(has_overlay); \
func(has_pipe_cxsr); \
func(has_pooled_eu); \
@@ -2250,8 +2251,9 @@ struct drm_i915_private {
wait_queue_head_t gmbus_wait_queue;
struct pci_dev *bridge_dev;
- struct i915_gem_context *kernel_context;
struct intel_engine_cs *engine[I915_NUM_ENGINES];
+ struct i915_gem_context *kernel_context;
+ struct i915_gem_context *preempt_context;
struct i915_vma *semaphore;
struct drm_dma_handle *status_page_dmah;
diff --git a/drivers/gpu/drm/i915/i915_gem_context.c b/drivers/gpu/drm/i915/i915_gem_context.c
index 921ee369c74d..1518e110fd04 100644
--- a/drivers/gpu/drm/i915/i915_gem_context.c
+++ b/drivers/gpu/drm/i915/i915_gem_context.c
@@ -416,14 +416,29 @@ i915_gem_context_create_gvt(struct drm_device *dev)
return ctx;
}
+static struct i915_gem_context *
+create_kernel_context(struct drm_i915_private *i915, int prio)
+{
+ struct i915_gem_context *ctx;
+
+ ctx = i915_gem_create_context(i915, NULL);
+ if (IS_ERR(ctx))
+ return ctx;
+
+ i915_gem_context_clear_bannable(ctx);
+ ctx->priority = prio;
+ ctx->ring_size = PAGE_SIZE;
+
+ return ctx;
+}
+
int i915_gem_contexts_init(struct drm_i915_private *dev_priv)
{
struct i915_gem_context *ctx;
/* Init should only be called once per module load. Eventually the
* restriction on the context_disabled check can be loosened. */
- if (WARN_ON(dev_priv->kernel_context))
- return 0;
+ GEM_BUG_ON(dev_priv->kernel_context);
INIT_LIST_HEAD(&dev_priv->contexts.list);
INIT_WORK(&dev_priv->contexts.free_work, contexts_free_worker);
@@ -441,23 +456,30 @@ int i915_gem_contexts_init(struct drm_i915_private *dev_priv)
BUILD_BUG_ON(MAX_CONTEXT_HW_ID > INT_MAX);
ida_init(&dev_priv->contexts.hw_ida);
- ctx = i915_gem_create_context(dev_priv, NULL);
+ /* lowest priority; idle task */
+ ctx = create_kernel_context(dev_priv, I915_PRIORITY_MIN);
if (IS_ERR(ctx)) {
DRM_ERROR("Failed to create default global context (error %ld)\n",
PTR_ERR(ctx));
return PTR_ERR(ctx);
}
- /* For easy recognisablity, we want the kernel context to be 0 and then
+ /*
+ * For easy recognisablity, we want the kernel context to be 0 and then
* all user contexts will have non-zero hw_id.
*/
GEM_BUG_ON(ctx->hw_id);
-
- i915_gem_context_clear_bannable(ctx);
- ctx->priority = I915_PRIORITY_MIN; /* lowest priority; idle task */
+ GEM_BUG_ON(!i915_gem_context_is_kernel(ctx));
dev_priv->kernel_context = ctx;
- GEM_BUG_ON(!i915_gem_context_is_kernel(ctx));
+ /* highest priority; preempting task */
+ ctx = create_kernel_context(dev_priv, INT_MAX);
+ if (IS_ERR(ctx)) {
+ DRM_ERROR("Failed to create default preempt context (error %ld)\n",
+ PTR_ERR(ctx));
+ return PTR_ERR(ctx);
+ }
+ dev_priv->preempt_context = ctx;
DRM_DEBUG_DRIVER("%s context support initialized\n",
dev_priv->engine[RCS]->context_size ? "logical" :
@@ -517,6 +539,10 @@ void i915_gem_contexts_fini(struct drm_i915_private *i915)
context_close(ctx);
i915_gem_context_free(ctx);
+ ctx = i915_gem_context_get(fetch_and_zero(&i915->preempt_context));
+ context_close(ctx);
+ i915_gem_context_free(ctx);
+
/* Must free all deferred contexts (via flush_workqueue) first */
ida_destroy(&i915->contexts.hw_ida);
}
diff --git a/drivers/gpu/drm/i915/i915_gem_request.c b/drivers/gpu/drm/i915/i915_gem_request.c
index 4eb1a76731b2..010ed68cc21b 100644
--- a/drivers/gpu/drm/i915/i915_gem_request.c
+++ b/drivers/gpu/drm/i915/i915_gem_request.c
@@ -587,6 +587,13 @@ i915_gem_request_alloc(struct intel_engine_cs *engine,
lockdep_assert_held(&dev_priv->drm.struct_mutex);
+ /*
+ * Preempt contexts are reserved for exclusive use to inject a
+ * preemption context switch. They are never to be used for any trivial
+ * request!
+ */
+ GEM_BUG_ON(ctx == dev_priv->preempt_context);
+
/* ABI: Before userspace accesses the GPU (e.g. execbuffer), report
* EIO if the GPU is already wedged.
*/
diff --git a/drivers/gpu/drm/i915/intel_engine_cs.c b/drivers/gpu/drm/i915/intel_engine_cs.c
index 21e037fc21b7..02eb25ed1064 100644
--- a/drivers/gpu/drm/i915/intel_engine_cs.c
+++ b/drivers/gpu/drm/i915/intel_engine_cs.c
@@ -613,9 +613,22 @@ int intel_engine_init_common(struct intel_engine_cs *engine)
if (IS_ERR(ring))
return PTR_ERR(ring);
+ /*
+ * Similarly the preempt context must always be available so that
+ * we can interrupt the engine at any time.
+ */
+ if (INTEL_INFO(engine->i915)->has_logical_ring_preemption) {
+ ring = engine->context_pin(engine,
+ engine->i915->preempt_context);
+ if (IS_ERR(ring)) {
+ ret = PTR_ERR(ring);
+ goto err_unpin_kernel;
+ }
+ }
+
ret = intel_engine_init_breadcrumbs(engine);
if (ret)
- goto err_unpin;
+ goto err_unpin_preempt;
ret = i915_gem_render_state_init(engine);
if (ret)
@@ -634,7 +647,10 @@ int intel_engine_init_common(struct intel_engine_cs *engine)
i915_gem_render_state_fini(engine);
err_breadcrumbs:
intel_engine_fini_breadcrumbs(engine);
-err_unpin:
+err_unpin_preempt:
+ if (INTEL_INFO(engine->i915)->has_logical_ring_preemption)
+ engine->context_unpin(engine, engine->i915->preempt_context);
+err_unpin_kernel:
engine->context_unpin(engine, engine->i915->kernel_context);
return ret;
}
@@ -660,6 +676,8 @@ void intel_engine_cleanup_common(struct intel_engine_cs *engine)
intel_engine_cleanup_cmd_parser(engine);
i915_gem_batch_pool_fini(&engine->batch_pool);
+ if (INTEL_INFO(engine->i915)->has_logical_ring_preemption)
+ engine->context_unpin(engine, engine->i915->preempt_context);
engine->context_unpin(engine, engine->i915->kernel_context);
}
--
2.14.1
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