drm/i915: Stop tracking timeline->inflight_seqnos
In commit 9b6586ae9f6b ("drm/i915: Keep a global seqno per-engine"), we
moved from a global inflight counter to per-engine counters in the
hope that will be easy to run concurrently in future. However, with the
advent of the desire to move requests between engines, we do need a
global counter to preserve the semantics that no engine wraps in the
middle of a submit. (Although this semantic is now only required for gen7
semaphore support, which only supports greater-then comparisons!)
v2: Keep a global counter of all requests ever submitted and force the
reset when it wraps.
References: 9b6586ae9f6b ("drm/i915: Keep a global seqno per-engine")
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20180430131503.5375-1-chris@chris-wilson.co.uk
diff --git a/drivers/gpu/drm/i915/i915_request.c b/drivers/gpu/drm/i915/i915_request.c
index b692a9f..b1993d4 100644
--- a/drivers/gpu/drm/i915/i915_request.c
+++ b/drivers/gpu/drm/i915/i915_request.c
@@ -241,6 +241,7 @@ static int reset_all_global_seqno(struct drm_i915_private *i915, u32 seqno)
sizeof(timeline->engine[id].global_sync));
}
+ i915->gt.request_serial = seqno;
return 0;
}
@@ -257,18 +258,22 @@ int i915_gem_set_global_seqno(struct drm_device *dev, u32 seqno)
return reset_all_global_seqno(i915, seqno - 1);
}
-static int reserve_engine(struct intel_engine_cs *engine)
+static int reserve_gt(struct drm_i915_private *i915)
{
- struct drm_i915_private *i915 = engine->i915;
- u32 active = ++engine->timeline->inflight_seqnos;
- u32 seqno = engine->timeline->seqno;
int ret;
- /* Reservation is fine until we need to wrap around */
- if (unlikely(add_overflows(seqno, active))) {
+ /*
+ * Reservation is fine until we may need to wrap around
+ *
+ * By incrementing the serial for every request, we know that no
+ * individual engine may exceed that serial (as each is reset to 0
+ * on any wrap). This protects even the most pessimistic of migrations
+ * of every request from all engines onto just one.
+ */
+ while (unlikely(++i915->gt.request_serial == 0)) {
ret = reset_all_global_seqno(i915, 0);
if (ret) {
- engine->timeline->inflight_seqnos--;
+ i915->gt.request_serial--;
return ret;
}
}
@@ -279,15 +284,10 @@ static int reserve_engine(struct intel_engine_cs *engine)
return 0;
}
-static void unreserve_engine(struct intel_engine_cs *engine)
+static void unreserve_gt(struct drm_i915_private *i915)
{
- struct drm_i915_private *i915 = engine->i915;
-
if (!--i915->gt.active_requests)
i915_gem_park(i915);
-
- GEM_BUG_ON(!engine->timeline->inflight_seqnos);
- engine->timeline->inflight_seqnos--;
}
void i915_gem_retire_noop(struct i915_gem_active *active,
@@ -362,7 +362,6 @@ static void i915_request_retire(struct i915_request *request)
list_del_init(&request->link);
spin_unlock_irq(&engine->timeline->lock);
- unreserve_engine(request->engine);
advance_ring(request);
free_capture_list(request);
@@ -424,6 +423,8 @@ static void i915_request_retire(struct i915_request *request)
}
spin_unlock_irq(&request->lock);
+ unreserve_gt(request->i915);
+
i915_sched_node_fini(request->i915, &request->sched);
i915_request_put(request);
}
@@ -642,7 +643,7 @@ i915_request_alloc(struct intel_engine_cs *engine, struct i915_gem_context *ctx)
return ERR_CAST(ring);
GEM_BUG_ON(!ring);
- ret = reserve_engine(engine);
+ ret = reserve_gt(i915);
if (ret)
goto err_unpin;
@@ -784,7 +785,7 @@ i915_request_alloc(struct intel_engine_cs *engine, struct i915_gem_context *ctx)
kmem_cache_free(i915->requests, rq);
err_unreserve:
- unreserve_engine(engine);
+ unreserve_gt(i915);
err_unpin:
engine->context_unpin(engine, ctx);
return ERR_PTR(ret);