[PATCH] drm/i915: Look for an active kernel context before switching
Chris Wilson
chris at chris-wilson.co.uk
Wed May 23 23:21:46 UTC 2018
We were not very carefully checking to see if an older request on the
engine was an earlier switch-to-kernel-context before deciding to emit a
new switch. The end result would be that we could get into a permanent
loop of trying to emit a new request to perform the switch simply to
flush the existing switch.
What we need is a means of tracking the completion of each timeline
versus the kernel context, that is to detect if a more recent request
has been submitted that would result in a switch away from the kernel
context. To realise this, we need only to look in our syncmap on the
kernel context and check that we have synchronized against all active
rings.
v2: Since all ringbuffer clients currently share the same timeline, we do
have to use the gem_context to distinguish clients.
As a bonus, include all the tracing used to debug the death inside
suspend.
v3: Test, test, test. Construct a selftest to exercise and assert the
expected behaviour that multiple switch-to-contexts do not emit
redundant requests.
Reported-by: Mika Kuoppala <mika.kuoppala at intel.com>
Fixes: a89d1f921c15 ("drm/i915: Split i915_gem_timeline into individual timelines")
Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
Cc: Mika Kuoppala <mika.kuoppala at intel.com>
---
drivers/gpu/drm/i915/i915_gem.c | 7 +
drivers/gpu/drm/i915/i915_gem_context.c | 67 ++++++--
drivers/gpu/drm/i915/i915_request.c | 5 +-
.../gpu/drm/i915/selftests/i915_gem_context.c | 160 ++++++++++++++++++
.../drm/i915/selftests/i915_mock_selftests.h | 1 +
5 files changed, 228 insertions(+), 12 deletions(-)
diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c
index 03874b50ada9..05f44ca35a06 100644
--- a/drivers/gpu/drm/i915/i915_gem.c
+++ b/drivers/gpu/drm/i915/i915_gem.c
@@ -3703,6 +3703,9 @@ static int wait_for_engines(struct drm_i915_private *i915)
int i915_gem_wait_for_idle(struct drm_i915_private *i915, unsigned int flags)
{
+ GEM_TRACE("flags=%x (%s)\n",
+ flags, flags & I915_WAIT_LOCKED ? "locked" : "unlocked");
+
/* If the device is asleep, we have no requests outstanding */
if (!READ_ONCE(i915->gt.awake))
return 0;
@@ -3719,6 +3722,7 @@ int i915_gem_wait_for_idle(struct drm_i915_private *i915, unsigned int flags)
return err;
}
i915_retire_requests(i915);
+ GEM_BUG_ON(i915->gt.active_requests);
return wait_for_engines(i915);
} else {
@@ -4901,6 +4905,7 @@ static void assert_kernel_context_is_current(struct drm_i915_private *i915)
struct intel_engine_cs *engine;
enum intel_engine_id id;
+ GEM_BUG_ON(i915->gt.active_requests);
for_each_engine(engine, i915, id) {
GEM_BUG_ON(__i915_gem_active_peek(&engine->timeline.last_request));
GEM_BUG_ON(engine->last_retired_context->gem_context != kctx);
@@ -4932,6 +4937,8 @@ int i915_gem_suspend(struct drm_i915_private *dev_priv)
struct drm_device *dev = &dev_priv->drm;
int ret;
+ GEM_TRACE("\n");
+
intel_runtime_pm_get(dev_priv);
intel_suspend_gt_powersave(dev_priv);
diff --git a/drivers/gpu/drm/i915/i915_gem_context.c b/drivers/gpu/drm/i915/i915_gem_context.c
index b69b18ef8120..82198bfacb7f 100644
--- a/drivers/gpu/drm/i915/i915_gem_context.c
+++ b/drivers/gpu/drm/i915/i915_gem_context.c
@@ -581,24 +581,58 @@ last_request_on_engine(struct i915_timeline *timeline,
rq = i915_gem_active_raw(&timeline->last_request,
&engine->i915->drm.struct_mutex);
- if (rq && rq->engine == engine)
+ if (rq && rq->engine == engine) {
+ GEM_TRACE("last request for %s on engine %s: %llx:%d\n",
+ timeline->name, engine->name,
+ rq->fence.context, rq->fence.seqno);
return rq;
+ }
return NULL;
}
-static bool engine_has_idle_kernel_context(struct intel_engine_cs *engine)
+static bool engine_has_kernel_context_barrier(struct intel_engine_cs *engine)
{
- struct list_head * const active_rings = &engine->i915->gt.active_rings;
+ struct drm_i915_private *i915 = engine->i915;
+ struct i915_timeline *barrier =
+ to_intel_context(i915->kernel_context, engine)->ring->timeline;
struct intel_ring *ring;
+ bool any_active = false;
- lockdep_assert_held(&engine->i915->drm.struct_mutex);
+ lockdep_assert_held(&i915->drm.struct_mutex);
+ list_for_each_entry(ring, &i915->gt.active_rings, active_link) {
+ struct i915_request *rq;
+
+ rq = last_request_on_engine(ring->timeline, engine);
+ if (!rq)
+ continue;
- list_for_each_entry(ring, active_rings, active_link) {
- if (last_request_on_engine(ring->timeline, engine))
+ if (rq->gem_context == i915->kernel_context)
+ continue;
+
+ /*
+ * Was this request submitted after the previous
+ * switch-to-kernel-context?
+ */
+ if (!i915_timeline_sync_is_later(barrier, &rq->fence)) {
+ GEM_TRACE("%s needs barrier\n", ring->timeline->name);
return false;
+ }
+
+ GEM_TRACE("%s has barrier\n", ring->timeline->name);
+ any_active = true;
}
+ /*
+ * If any other timeline was still active and behind the last barrier,
+ * then our last switch-to-kernel-context must still be queued and
+ * will run last (leaving the engine in the kernel context when it
+ * eventually idles).
+ */
+ if (any_active)
+ return true;
+
+ /* The engine is idle; check that it is idling in the kernel context. */
return intel_engine_has_kernel_context(engine);
}
@@ -607,7 +641,10 @@ int i915_gem_switch_to_kernel_context(struct drm_i915_private *i915)
struct intel_engine_cs *engine;
enum intel_engine_id id;
+ GEM_TRACE("\n");
+
lockdep_assert_held(&i915->drm.struct_mutex);
+ GEM_BUG_ON(!i915->kernel_context);
i915_retire_requests(i915);
@@ -615,9 +652,12 @@ int i915_gem_switch_to_kernel_context(struct drm_i915_private *i915)
struct intel_ring *ring;
struct i915_request *rq;
- if (engine_has_idle_kernel_context(engine))
+ GEM_BUG_ON(!to_intel_context(i915->kernel_context, engine));
+ if (engine_has_kernel_context_barrier(engine))
continue;
+ GEM_TRACE("emit barrier on %s\n", engine->name);
+
rq = i915_request_alloc(engine, i915->kernel_context);
if (IS_ERR(rq))
return PTR_ERR(rq);
@@ -627,10 +667,15 @@ int i915_gem_switch_to_kernel_context(struct drm_i915_private *i915)
struct i915_request *prev;
prev = last_request_on_engine(ring->timeline, engine);
- if (prev)
- i915_sw_fence_await_sw_fence_gfp(&rq->submit,
- &prev->submit,
- I915_FENCE_GFP);
+ if (!prev)
+ continue;
+
+ if (prev->gem_context == i915->kernel_context)
+ continue;
+
+ i915_sw_fence_await_sw_fence_gfp(&rq->submit,
+ &prev->submit,
+ I915_FENCE_GFP);
}
/*
diff --git a/drivers/gpu/drm/i915/i915_request.c b/drivers/gpu/drm/i915/i915_request.c
index fc499bcbd105..f187250e60c6 100644
--- a/drivers/gpu/drm/i915/i915_request.c
+++ b/drivers/gpu/drm/i915/i915_request.c
@@ -320,6 +320,7 @@ static void advance_ring(struct i915_request *request)
* is just about to be. Either works, if we miss the last two
* noops - they are safe to be replayed on a reset.
*/
+ GEM_TRACE("marking %s as inactive\n", ring->timeline->name);
tail = READ_ONCE(request->tail);
list_del(&ring->active_link);
} else {
@@ -1095,8 +1096,10 @@ void __i915_request_add(struct i915_request *request, bool flush_caches)
i915_gem_active_set(&timeline->last_request, request);
list_add_tail(&request->ring_link, &ring->request_list);
- if (list_is_first(&request->ring_link, &ring->request_list))
+ if (list_is_first(&request->ring_link, &ring->request_list)) {
+ GEM_TRACE("marking %s as active\n", ring->timeline->name);
list_add(&ring->active_link, &request->i915->gt.active_rings);
+ }
request->emitted_jiffies = jiffies;
/*
diff --git a/drivers/gpu/drm/i915/selftests/i915_gem_context.c b/drivers/gpu/drm/i915/selftests/i915_gem_context.c
index ddb03f009232..633e568d1f75 100644
--- a/drivers/gpu/drm/i915/selftests/i915_gem_context.c
+++ b/drivers/gpu/drm/i915/selftests/i915_gem_context.c
@@ -26,6 +26,7 @@
#include "igt_flush_test.h"
#include "mock_drm.h"
+#include "mock_gem_device.h"
#include "huge_gem_object.h"
#define DW_PER_PAGE (PAGE_SIZE / sizeof(u32))
@@ -420,6 +421,146 @@ static int igt_ctx_exec(void *arg)
return err;
}
+static int igt_switch_to_kernel_context(void *arg)
+{
+ struct drm_i915_private *i915 = arg;
+ struct intel_engine_cs *engine;
+ struct i915_gem_context *ctx;
+ enum intel_engine_id id;
+ struct drm_file *file;
+ int err;
+
+ /*
+ * A core premise of switching to the kernel context is that
+ * if an engine is already idling in the kernel context, we
+ * do not emit another request and wake it up.
+ */
+
+ file = mock_file(i915);
+ if (IS_ERR(file))
+ return PTR_ERR(file);
+
+ mutex_lock(&i915->drm.struct_mutex);
+ ctx = i915_gem_create_context(i915, file->driver_priv);
+
+ /* First check idling each individual engine */
+ for_each_engine(engine, i915, id) {
+ struct i915_request *rq;
+
+ rq = i915_request_alloc(engine, ctx);
+ if (IS_ERR(rq)) {
+ err = PTR_ERR(rq);
+ goto out_unlock;
+ }
+ i915_request_add(rq);
+
+ err = i915_gem_switch_to_kernel_context(i915);
+ if (err)
+ goto out_unlock;
+
+ if (!intel_engine_has_kernel_context(engine)) {
+ pr_err("kernel context not last on engine %s!\n",
+ engine->name);
+ err = -EINVAL;
+ goto out_unlock;
+ }
+
+ err = i915_gem_wait_for_idle(i915, I915_WAIT_LOCKED);
+ if (err)
+ goto out_unlock;
+
+ GEM_BUG_ON(i915->gt.active_requests);
+
+ err = i915_gem_switch_to_kernel_context(i915);
+ if (err)
+ goto out_unlock;
+
+ if (i915->gt.active_requests) {
+ pr_err("switch-to-kernel-context emitted %d requests even though it should already be idling in the kernel context\n",
+ i915->gt.active_requests);
+ err = -EINVAL;
+ goto out_unlock;
+ }
+
+ if (!intel_engine_has_kernel_context(engine)) {
+ pr_err("kernel context not last on engine %s!\n",
+ engine->name);
+ err = -EINVAL;
+ goto out_unlock;
+ }
+ }
+
+ /* Now en masse */
+ for_each_engine(engine, i915, id) {
+ struct i915_request *rq;
+
+ rq = i915_request_alloc(engine, ctx);
+ if (IS_ERR(rq)) {
+ err = PTR_ERR(rq);
+ goto out_unlock;
+ }
+ i915_request_add(rq);
+ }
+
+ err = i915_gem_switch_to_kernel_context(i915);
+ if (err)
+ goto out_unlock;
+
+ for_each_engine(engine, i915, id) {
+ if (!intel_engine_has_kernel_context(engine)) {
+ pr_err("kernel context not last on engine %s!\n",
+ engine->name);
+ err = -EINVAL;
+ goto out_unlock;
+ }
+ }
+
+ err = i915_gem_wait_for_idle(i915, I915_WAIT_LOCKED);
+ if (err)
+ goto out_unlock;
+
+ GEM_BUG_ON(i915->gt.active_requests);
+ for_each_engine(engine, i915, id) {
+ if (engine->last_retired_context->gem_context != i915->kernel_context) {
+ pr_err("kernel context not last retired on engine %s!\n",
+ engine->name);
+ err = -EINVAL;
+ goto out_unlock;
+ }
+ }
+
+ err = i915_gem_switch_to_kernel_context(i915);
+ if (err)
+ goto out_unlock;
+
+ if (i915->gt.active_requests) {
+ pr_err("switch-to-kernel-context emitted %d requests even though it should already be idling in the kernel context\n",
+ i915->gt.active_requests);
+ err = -EINVAL;
+ goto out_unlock;
+ }
+
+ for_each_engine(engine, i915, id) {
+ if (!intel_engine_has_kernel_context(engine)) {
+ pr_err("kernel context not last on engine %s!\n",
+ engine->name);
+ err = -EINVAL;
+ goto out_unlock;
+ }
+ }
+
+out_unlock:
+ if (err)
+ GEM_TRACE_DUMP();
+ if (igt_flush_test(i915, I915_WAIT_LOCKED))
+ err = -EIO;
+ mutex_unlock(&i915->drm.struct_mutex);
+
+ mock_file_free(i915, file);
+ return err;
+}
+
+
static int fake_aliasing_ppgtt_enable(struct drm_i915_private *i915)
{
struct drm_i915_gem_object *obj;
@@ -447,9 +588,28 @@ static void fake_aliasing_ppgtt_disable(struct drm_i915_private *i915)
i915_gem_fini_aliasing_ppgtt(i915);
}
+int i915_gem_context_mock_selftests(void)
+{
+ static const struct i915_subtest tests[] = {
+ SUBTEST(igt_switch_to_kernel_context),
+ };
+ struct drm_i915_private *i915;
+ int err;
+
+ i915 = mock_gem_device();
+ if (!i915)
+ return -ENOMEM;
+
+ err = i915_subtests(tests, i915);
+
+ drm_dev_unref(&i915->drm);
+ return err;
+}
+
int i915_gem_context_live_selftests(struct drm_i915_private *dev_priv)
{
static const struct i915_subtest tests[] = {
+ SUBTEST(igt_switch_to_kernel_context),
SUBTEST(igt_ctx_exec),
};
bool fake_alias = false;
diff --git a/drivers/gpu/drm/i915/selftests/i915_mock_selftests.h b/drivers/gpu/drm/i915/selftests/i915_mock_selftests.h
index d16d74178e9d..1b70208eeea7 100644
--- a/drivers/gpu/drm/i915/selftests/i915_mock_selftests.h
+++ b/drivers/gpu/drm/i915/selftests/i915_mock_selftests.h
@@ -24,3 +24,4 @@ selftest(vma, i915_vma_mock_selftests)
selftest(evict, i915_gem_evict_mock_selftests)
selftest(gtt, i915_gem_gtt_mock_selftests)
selftest(hugepages, i915_gem_huge_page_mock_selftests)
+selftest(contexts, i915_gem_context_mock_selftests)
--
2.17.0
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