From 6b567085c1bdbacea217dd628f0dbf26dd67db3f Mon Sep 17 00:00:00 2001
From: Chris Wilson <chris@chris-wilson.co.uk>
Date: Thu, 8 Jun 2017 12:14:05 +0100
Subject: [PATCH] drm/i915: Remove the spin-request during execbuf await_request
Git-commit: 6b567085c1bdbacea217dd628f0dbf26dd67db3f
Patch-mainline: v4.13-rc1
References: FATE#322643 bsc#1055900

Originally we would enable and disable the breadcrumb interrupt
immediately on demand. This was slow enough to have a large impact
(>30%) on tasks that hopped between engines. However, by using a shadow
to keep the irq alive for an extra interrupt (see commit 67b807a89230
("drm/i915: Delay disabling the user interrupt for breadcrumbs")) and
by recently reducing the cost in adding ourselves to the signal tree, we
no longer need to spin-request during await_request to avoid delays in
throughput tests. Without the earlier patches to stop the wakeup when
signaling if the irq was already active, we saw no improvement in
execbuf overhead (and corresponding contention in other clients) despite
the removal of the spinner in a simple test like glxgears. This means
there will be scenarios where now we spend longer enabling the interrupt
than we would have spent spinning, but these are not likely to have as
noticeable an impact as the high frequency test cases (where there
should not be any regression).

Ulterior motive: generalising the engine->sync_to to handle different
types of semaphores and non-semaphores.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Cc: Oscar Mateo <oscar.mateo@intel.com>
Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Reviewed-by: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/20170608111405.16466-4-chris@chris-wilson.co.uk
Acked-by: Takashi Iwai <tiwai@suse.de>

---
 drivers/gpu/drm/i915/i915_gem_request.c |   18 ++++++------------
 1 file changed, 6 insertions(+), 12 deletions(-)

--- a/drivers/gpu/drm/i915/i915_gem_request.c
+++ b/drivers/gpu/drm/i915/i915_gem_request.c
@@ -683,7 +683,6 @@ static int
 i915_gem_request_await_request(struct drm_i915_gem_request *to,
 			       struct drm_i915_gem_request *from)
 {
-	u32 seqno;
 	int ret;
 
 	GEM_BUG_ON(to == from);
@@ -707,18 +706,14 @@ i915_gem_request_await_request(struct dr
 		return ret < 0 ? ret : 0;
 	}
 
-	seqno = i915_gem_request_global_seqno(from);
-	if (!seqno)
-		goto await_dma_fence;
+	if (to->engine->semaphore.sync_to) {
+		u32 seqno;
 
-	if (!to->engine->semaphore.sync_to) {
-		if (!__i915_gem_request_started(from, seqno))
-			goto await_dma_fence;
+		GEM_BUG_ON(!from->engine->semaphore.signal);
 
-		if (!__i915_spin_request(from, seqno, TASK_INTERRUPTIBLE, 2))
+		seqno = i915_gem_request_global_seqno(from);
+		if (!seqno)
 			goto await_dma_fence;
-	} else {
-		GEM_BUG_ON(!from->engine->semaphore.signal);
 
 		if (seqno <= to->timeline->global_sync[from->engine->id])
 			return 0;
@@ -729,10 +724,9 @@ i915_gem_request_await_request(struct dr
 			return ret;
 
 		to->timeline->global_sync[from->engine->id] = seqno;
+		return 0;
 	}
 
-	return 0;
-
 await_dma_fence:
 	ret = i915_sw_fence_await_dma_fence(&to->submit,
 					    &from->fence, 0,