[Intel-gfx] [PATCH 4/5] drm/i915/gem: Assign context id for async work

[Chris Wilson]

Allocate a few dma fence context id that we can use to associate async work
[for the CPU] launched on behalf of this context. For extra fun, we allow
a configurable concurrency width.

A current example would be that we spawn an unbound worker for every
userptr get_pages. In the future, we wish to charge this work to the
context that initiated the async work and to impose concurrency limits
based on the context.

Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
---
 drivers/gpu/drm/i915/gem/i915_gem_context.c       | 4 ++++
 drivers/gpu/drm/i915/gem/i915_gem_context.h       | 6 ++++++
 drivers/gpu/drm/i915/gem/i915_gem_context_types.h | 6 ++++++
 3 files changed, 16 insertions(+)

diff --git a/drivers/gpu/drm/i915/gem/i915_gem_context.c b/drivers/gpu/drm/i915/gem/i915_gem_context.c
index 11d9135cf21a..4e3257b79791 100644
--- a/drivers/gpu/drm/i915/gem/i915_gem_context.c
+++ b/drivers/gpu/drm/i915/gem/i915_gem_context.c
@@ -717,6 +717,10 @@ __create_context(struct drm_i915_private *i915)
 	ctx->sched.priority = I915_USER_PRIORITY(I915_PRIORITY_NORMAL);
 	mutex_init(&ctx->mutex);
 
+	ctx->async.width = rounddown_pow_of_two(num_online_cpus());
+	ctx->async.context = dma_fence_context_alloc(ctx->async.width);
+	ctx->async.width--;
+
 	spin_lock_init(&ctx->stale.lock);
 	INIT_LIST_HEAD(&ctx->stale.engines);
 
diff --git a/drivers/gpu/drm/i915/gem/i915_gem_context.h b/drivers/gpu/drm/i915/gem/i915_gem_context.h
index 3702b2fb27ab..e104ff0ae740 100644
--- a/drivers/gpu/drm/i915/gem/i915_gem_context.h
+++ b/drivers/gpu/drm/i915/gem/i915_gem_context.h
@@ -134,6 +134,12 @@ int i915_gem_context_setparam_ioctl(struct drm_device *dev, void *data,
 int i915_gem_context_reset_stats_ioctl(struct drm_device *dev, void *data,
 				       struct drm_file *file);
 
+static inline u64 i915_gem_context_async_id(struct i915_gem_context *ctx)
+{
+	return (ctx->async.context +
+		(atomic_fetch_inc(&ctx->async.cur) & ctx->async.width));
+}
+
 static inline struct i915_gem_context *
 i915_gem_context_get(struct i915_gem_context *ctx)
 {
diff --git a/drivers/gpu/drm/i915/gem/i915_gem_context_types.h b/drivers/gpu/drm/i915/gem/i915_gem_context_types.h
index 28760bd03265..5f5cfa3a3e9b 100644
--- a/drivers/gpu/drm/i915/gem/i915_gem_context_types.h
+++ b/drivers/gpu/drm/i915/gem/i915_gem_context_types.h
@@ -85,6 +85,12 @@ struct i915_gem_context {
 
 	struct intel_timeline *timeline;
 
+	struct {
+		u64 context;
+		atomic_t cur;
+		unsigned int width;
+	} async;
+
 	/**
 	 * @vm: unique address space (GTT)
 	 *
-- 
2.20.1