drm/i915: Remove obsolete ringbuffer emission for gen8+

Since removing the module parameter to force selection of ringbuffer
emission for gen8, the code is defunct. Remove it.

To put the difference into perspective, a couple of microbenchmarks
(bdw i7-5557u, 20170324):
                                        ring          execlists
exec continuous nops on all rings:   1.491us            2.223us
exec sequential nops on each ring:  12.508us           53.682us
single nop + sync:                   9.272us           30.291us

vblank_mode=0 glxgears:            ~11000fps           ~9000fps

Since the earlier submission, gen8 ringbuffer submission has fallen
further and further behind in features. So while ringbuffer may hold the
throughput crown, in terms of interactive latency, execlists is much
better. Alas, we have no convenient metrics for such, other than
demonstrating things we can do with execlists but can not using
legacy ringbuffer submission.

We have made a few improvements to lowlevel execlists throughput,
and ringbuffer currently panics on boot! (bdw i7-5557u, 20171026):

                                        ring          execlists
exec continuous nops on all rings:       n/a            1.921us
exec sequential nops on each ring:       n/a           44.621us
single nop + sync:                       n/a           21.953us

vblank_mode=0 glxgears:                  n/a          ~18500fps

References: https://bugs.freedesktop.org/show_bug.cgi?id=87725
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Once-upon-a-time-Reviewed-by: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Reviewed-by: Mika Kuoppala <mika.kuoppala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20171120205504.21892-2-chris@chris-wilson.co.uk

1 files changed, 6 insertions, 41 deletions

diff --git a/drivers/gpu/drm/i915/i915_gem_context.c b/drivers/gpu/drm/i915/i915_gem_context.c
index c75941d3d7e7..0704d9af261b 100644
--- a/drivers/gpu/drm/i915/i915_gem_context.c
+++ b/drivers/gpu/drm/i915/i915_gem_context.c
@@ -574,21 +574,21 @@ mi_set_context(struct drm_i915_gem_request *req, u32 flags)
 	enum intel_engine_id id;
 	const int num_rings =
 		/* Use an extended w/a on gen7 if signalling from other rings */
-		(i915_modparams.semaphores && INTEL_GEN(dev_priv) == 7) ?
+		(i915_modparams.semaphores && IS_GEN7(dev_priv)) ?
 		INTEL_INFO(dev_priv)->num_rings - 1 :
 		0;
 	int len;
 	u32 *cs;
 
 	flags |= MI_MM_SPACE_GTT;
-	if (IS_HASWELL(dev_priv) || INTEL_GEN(dev_priv) >= 8)
+	if (IS_HASWELL(dev_priv))
 		/* These flags are for resource streamer on HSW+ */
 		flags |= HSW_MI_RS_SAVE_STATE_EN | HSW_MI_RS_RESTORE_STATE_EN;
 	else
 		flags |= MI_SAVE_EXT_STATE_EN | MI_RESTORE_EXT_STATE_EN;
 
 	len = 4;
-	if (INTEL_GEN(dev_priv) >= 7)
+	if (IS_GEN7(dev_priv))
 		len += 2 + (num_rings ? 4*num_rings + 6 : 0);
 
 	cs = intel_ring_begin(req, len);
@@ -596,7 +596,7 @@ mi_set_context(struct drm_i915_gem_request *req, u32 flags)
 		return PTR_ERR(cs);
 
 	/* WaProgramMiArbOnOffAroundMiSetContext:ivb,vlv,hsw,bdw,chv */
-	if (INTEL_GEN(dev_priv) >= 7) {
+	if (IS_GEN7(dev_priv)) {
 		*cs++ = MI_ARB_ON_OFF | MI_ARB_DISABLE;
 		if (num_rings) {
 			struct intel_engine_cs *signaller;
@@ -623,7 +623,7 @@ mi_set_context(struct drm_i915_gem_request *req, u32 flags)
 	 */
 	*cs++ = MI_NOOP;
 
-	if (INTEL_GEN(dev_priv) >= 7) {
+	if (IS_GEN7(dev_priv)) {
 		if (num_rings) {
 			struct intel_engine_cs *signaller;
 			i915_reg_t last_reg = {}; /* keep gcc quiet */
@@ -714,27 +714,7 @@ needs_pd_load_pre(struct i915_hw_ppgtt *ppgtt, struct intel_engine_cs *engine)
 	if (engine->id != RCS)
 		return true;
 
-	if (INTEL_GEN(engine->i915) < 8)
-		return true;
-
-	return false;
-}
-
-static bool
-needs_pd_load_post(struct i915_hw_ppgtt *ppgtt,
-		   struct i915_gem_context *to,
-		   u32 hw_flags)
-{
-	if (!ppgtt)
-		return false;
-
-	if (!IS_GEN8(to->i915))
-		return false;
-
-	if (hw_flags & MI_RESTORE_INHIBIT)
-		return true;
-
-	return false;
+	return true;
 }
 
 static int do_rcs_switch(struct drm_i915_gem_request *req)
@@ -784,21 +764,6 @@ static int do_rcs_switch(struct drm_i915_gem_request *req)
 		engine->legacy_active_context = to;
 	}
 
-	/* GEN8 does *not* require an explicit reload if the PDPs have been
-	 * setup, and we do not wish to move them.
-	 */
-	if (needs_pd_load_post(ppgtt, to, hw_flags)) {
-		trace_switch_mm(engine, to);
-		ret = ppgtt->switch_mm(ppgtt, req);
-		/* The hardware context switch is emitted, but we haven't
-		 * actually changed the state - so it's probably safe to bail
-		 * here. Still, let the user know something dangerous has
-		 * happened.
-		 */
-		if (ret)
-			return ret;
-	}
-
 	if (ppgtt)
 		ppgtt->pd_dirty_rings &= ~intel_engine_flag(engine);