Chris Wilson <chris@xxxxxxxxxxxxxxxxxx> writes:
> 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@xxxxxxxxx>
> Fixes: a89d1f921c15 ("drm/i915: Split i915_gem_timeline into individual timelines")
> Signed-off-by: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx>
> Cc: Mika Kuoppala <mika.kuoppala@xxxxxxxxx>
> ---
> drivers/gpu/drm/i915/i915_gem.c | 7 +
> drivers/gpu/drm/i915/i915_gem.h | 3 +
> drivers/gpu/drm/i915/i915_gem_context.c | 86 +++++++++--
> drivers/gpu/drm/i915/i915_request.c | 5 +-
> .../gpu/drm/i915/selftests/i915_gem_context.c | 144 ++++++++++++++++++
> .../drm/i915/selftests/i915_mock_selftests.h | 1 +
> 6 files changed, 231 insertions(+), 15 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.h b/drivers/gpu/drm/i915/i915_gem.h
> index 5bf24cfc218c..62ee4e385365 100644
> --- a/drivers/gpu/drm/i915/i915_gem.h
> +++ b/drivers/gpu/drm/i915/i915_gem.h
> @@ -63,9 +63,12 @@ struct drm_i915_private;
> #if IS_ENABLED(CONFIG_DRM_I915_TRACE_GEM)
> #define GEM_TRACE(...) trace_printk(__VA_ARGS__)
> #define GEM_TRACE_DUMP() ftrace_dump(DUMP_ALL)
> +#define GEM_TRACE_DUMP_ON(expr) \
> + do { if (expr) ftrace_dump(DUMP_ALL); } while (0)
> #else
> #define GEM_TRACE(...) do { } while (0)
> #define GEM_TRACE_DUMP() do { } while (0)
> +#define GEM_TRACE_DUMP_ON(expr) BUILD_BUG_ON_INVALID(expr)
> #endif
>
> #define I915_NUM_ENGINES 8
> diff --git a/drivers/gpu/drm/i915/i915_gem_context.c b/drivers/gpu/drm/i915/i915_gem_context.c
> index b69b18ef8120..45393f6e0208 100644
> --- a/drivers/gpu/drm/i915/i915_gem_context.c
> +++ b/drivers/gpu/drm/i915/i915_gem_context.c
> @@ -576,30 +576,72 @@ last_request_on_engine(struct i915_timeline *timeline,
> {
> struct i915_request *rq;
>
> - if (timeline == &engine->timeline)
> - return NULL;
> + GEM_BUG_ON(timeline == &engine->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);
> + GEM_BUG_ON(rq->timeline != timeline);
> 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;
> + const struct intel_context * const ce =
> + to_intel_context(i915->kernel_context, engine);
> + struct i915_timeline *barrier = ce->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))
> + any_active = true;
> +
> + 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 for %llx:%d\n",
> + ring->timeline->name,
> + rq->fence.context,
> + rq->fence.seqno);
> return false;
> + }
> +
> + GEM_TRACE("%s has barrier after %llx:%d\n",
> + ring->timeline->name,
> + rq->fence.context,
> + rq->fence.seqno);
> }
>
> - return intel_engine_has_kernel_context(engine);
> + /*
> + * 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 engine->last_retired_context == ce;
> }
>
> int i915_gem_switch_to_kernel_context(struct drm_i915_private *i915)
> @@ -607,7 +649,10 @@ 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 +660,12 @@ 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 +675,20 @@ 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;
> +
> + GEM_TRACE("add barrier on %s for %llx:%d\n",
> + engine->name,
> + prev->fence.context,
> + prev->fence.seqno);
> + i915_sw_fence_await_sw_fence_gfp(&rq->submit,
> + &prev->submit,
> + I915_FENCE_GFP);
> + i915_timeline_sync_set(rq->timeline, &prev->fence);
> }
>
> /*
> 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..98a33a8fb046 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 +421,130 @@ static int igt_ctx_exec(void *arg)
> return err;
> }
>
> +static const char *__engine_name(struct drm_i915_private *i915,
> + unsigned int engines)
> +{
> + struct intel_engine_cs *engine;
> + unsigned int tmp;
> +
> + if (engines == ALL_ENGINES)
> + return "all";
> +
> + for_each_engine_masked(engine, i915, engines, tmp)
> + return engine->name;
> +
> + return "none";
> +}
> +
> +static int __igt_switch_to_kernel_context(struct drm_i915_private *i915,
> + struct i915_gem_context *ctx,
> + unsigned int engines)
> +{
> + struct intel_engine_cs *engine;
> + unsigned int tmp;
> + int err;
> +
> + GEM_TRACE("Testing %s\n", __engine_name(i915, engines));
> + for_each_engine_masked(engine, i915, engines, tmp) {
> + struct i915_request *rq;
> +
> + rq = i915_request_alloc(engine, ctx);
> + if (IS_ERR(rq))
> + return PTR_ERR(rq);
> +
> + i915_request_add(rq);
> + }
> +
> + err = i915_gem_switch_to_kernel_context(i915);
> + if (err)
> + return err;
> +
> + for_each_engine_masked(engine, i915, engines, tmp) {
> + if (!engine_has_kernel_context_barrier(engine)) {
> + pr_err("kernel context not last on engine %s!\n",
> + engine->name);
> + return -EINVAL;
> + }
> + }
> +
> + err = i915_gem_wait_for_idle(i915, I915_WAIT_LOCKED);
> + if (err)
> + return err;
> +
> + GEM_BUG_ON(i915->gt.active_requests);
> + for_each_engine_masked(engine, i915, engines, tmp) {
> + if (engine->last_retired_context->gem_context != i915->kernel_context) {
> + pr_err("engine %s not idling in kernel context!\n",
> + engine->name);
> + return -EINVAL;
> + }
> + }
> +
> + err = i915_gem_switch_to_kernel_context(i915);
> + if (err)
> + return err;
> +
> + 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);
> + return -EINVAL;
> + }
> +
> + for_each_engine_masked(engine, i915, engines, tmp) {
> + if (!intel_engine_has_kernel_context(engine)) {
> + pr_err("kernel context not last on engine %s!\n",
> + engine->name);
> + return -EINVAL;
> + }
> + }
> +
> + return 0;
> +}
> +
> +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;
> + 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. The other being
> + * that we do indeed end up idling in the kernel context.
> + */
> +
> + mutex_lock(&i915->drm.struct_mutex);
As discussed in irc,
Add comment or rename the ctx here and in __igt_switch_to_kernel_context
so that the reader knows that this mock kernel context is
used as convenient way to inject test requests.
Reviewed-by: Mika Kuoppala <mika.kuoppala@xxxxxxxxxxxxxxx>
> + ctx = kernel_context(i915);
> + if (IS_ERR(ctx)) {
> + err = PTR_ERR(ctx);
> + goto out_unlock;
> + }
> +
> + /* First check idling each individual engine */
> + for_each_engine(engine, i915, id) {
> + err = __igt_switch_to_kernel_context(i915, ctx, BIT(id));
> + if (err)
> + goto out_unlock;
> + }
> +
> + /* Now en masse */
> + err = __igt_switch_to_kernel_context(i915, ctx, ALL_ENGINES);
> + if (err)
> + goto out_unlock;
> +
> +out_unlock:
> + GEM_TRACE_DUMP_ON(err);
> + if (igt_flush_test(i915, I915_WAIT_LOCKED))
> + err = -EIO;
> + mutex_unlock(&i915->drm.struct_mutex);
> +
> + kernel_context_close(ctx);
> + return err;
> +}
> +
> static int fake_aliasing_ppgtt_enable(struct drm_i915_private *i915)
> {
> struct drm_i915_gem_object *obj;
> @@ -447,9 +572,28 @@ 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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