[Intel-gfx] [PATCH] drm/i915/gem: Reduce flush_ggtt() from a wait-for-idle to a mere barrier flush

[Chris Wilson]

Since we use barriers, we need only explicitly flush those barriers to
ensure tha we can reclaim the available ggtt for ourselves. The barrier
flush was implicit inside the intel_gt_wait_for_idle() -- except because
we use i915_gem_evict from inside an active timeline during execbuf, we
could easily end up waiting upon ourselves.

Fixes: 7936a22dd466 ("drm/i915/gt: Wait for new requests in intel_gt_retire_requests()")
Fixes: a46bfdc83fee ("drm/i915/gt: Wait for new requests in intel_gt_retire_requests()")
Testcase: igt/gem_exec_reloc/basic-range
Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
Cc: Tvrtko Ursulin <tvrtko.ursulin at intel.com>
---
 drivers/gpu/drm/i915/i915_gem_evict.c | 26 +++++++++++++-------------
 1 file changed, 13 insertions(+), 13 deletions(-)

diff --git a/drivers/gpu/drm/i915/i915_gem_evict.c b/drivers/gpu/drm/i915/i915_gem_evict.c
index 7e62c310290f..78ca56c06a3c 100644
--- a/drivers/gpu/drm/i915/i915_gem_evict.c
+++ b/drivers/gpu/drm/i915/i915_gem_evict.c
@@ -28,7 +28,7 @@
 
 #include <drm/i915_drm.h>
 
-#include "gem/i915_gem_context.h"
+#include "gt/intel_engine_heartbeat.h"
 #include "gt/intel_gt_requests.h"
 
 #include "i915_drv.h"
@@ -38,8 +38,11 @@ I915_SELFTEST_DECLARE(static struct igt_evict_ctl {
 	bool fail_if_busy:1;
 } igt_evict_ctl;)
 
-static int ggtt_flush(struct intel_gt *gt)
+static void ggtt_flush(struct intel_gt *gt)
 {
+	struct intel_engine_cs *engine;
+	enum intel_engine_id id;
+
 	/*
 	 * Not everything in the GGTT is tracked via vma (otherwise we
 	 * could evict as required with minimal stalling) so we are forced
@@ -47,7 +50,11 @@ static int ggtt_flush(struct intel_gt *gt)
 	 * the hopes that we can then remove contexts and the like only
 	 * bound by their active reference.
 	 */
-	return intel_gt_wait_for_idle(gt, MAX_SCHEDULE_TIMEOUT);
+	intel_gt_retire_requests(gt);
+	for_each_engine(engine, gt, id)
+		intel_engine_flush_barriers(engine);
+
+	cond_resched();
 }
 
 static bool
@@ -197,11 +204,7 @@ i915_gem_evict_something(struct i915_address_space *vm,
 	if (I915_SELFTEST_ONLY(igt_evict_ctl.fail_if_busy))
 		return -EBUSY;
 
-	ret = ggtt_flush(vm->gt);
-	if (ret)
-		return ret;
-
-	cond_resched();
+	ggtt_flush(vm->gt);
 
 	flags |= PIN_NONBLOCK;
 	goto search_again;
@@ -371,11 +374,8 @@ int i915_gem_evict_vm(struct i915_address_space *vm)
 	 * pin themselves inside the global GTT and performing the
 	 * switch otherwise is ineffective.
 	 */
-	if (i915_is_ggtt(vm)) {
-		ret = ggtt_flush(vm->gt);
-		if (ret)
-			return ret;
-	}
+	if (i915_is_ggtt(vm))
+		ggtt_flush(vm->gt);
 
 	INIT_LIST_HEAD(&eviction_list);
 	list_for_each_entry(vma, &vm->bound_list, vm_link) {
-- 
2.24.0