dri: Enable triple-bufferred pageflips

By popular demand.

Triple-buffering trade-offs output latency versus jitter. By having a
pre-rendered frame ready to swap in following a pageflip, we avoid the
scenario where the latency between receiving the flip complete signal
from the kernel, waking up the vsynced application, it render the new
frame and then for the server to process the swap request is greater
than the frame interval, causing us to miss the vblank. The result is
that application can become frame-locked to 30fps. Instead, we report to
the application that the first frame swap is immediately completed,
supply a new back buffer (or else the rendering would be blocked on
waiting for the front-buffer to be swapped away from the scanout) and
let them proceed to render the second frame. The second frame is added
to the swap queue, and the client throttled to vrefresh. (If the client
missed the vblank, the swap queue is empty and the client is immediately
woken again, whilst the pageflip is pending.)

Note, for practical reasons this only applies to page-flipping, for
example, calls to glXSwapBuffer() on fullscreen applications.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>

1 files changed, 173 insertions, 124 deletions

diff --git a/src/intel_dri.c b/src/intel_dri.c
index 38d7a6bc..0b284524 100644
--- a/src/intel_dri.c
+++ b/src/intel_dri.c
@@ -732,15 +732,21 @@ i830_dri2_add_frame_event(DRI2FrameEventPtr info)
 }
 
 static void
-i830_dri2_del_frame_event(DRI2FrameEventPtr info)
+i830_dri2_del_frame_event(DrawablePtr drawable, DRI2FrameEventPtr info)
 {
 	list_del(&info->client_resource);
 	list_del(&info->drawable_resource);
+
+	if (info->front)
+		I830DRI2DestroyBuffer(drawable, info->front);
+	if (info->back)
+		I830DRI2DestroyBuffer(drawable, info->back);
+
+	free(info);
 }
 
 static void
-I830DRI2ExchangeBuffers(DrawablePtr draw, DRI2BufferPtr front,
-			DRI2BufferPtr back)
+I830DRI2ExchangeBuffers(DrawablePtr draw, DRI2BufferPtr front, DRI2BufferPtr back)
 {
 	I830DRI2BufferPrivatePtr front_priv, back_priv;
 	struct intel_pixmap *front_intel, *back_intel;
@@ -760,20 +766,18 @@ I830DRI2ExchangeBuffers(DrawablePtr draw, DRI2BufferPtr front,
 	front_intel = intel_get_pixmap_private(front_priv->pixmap);
 	back_intel = intel_get_pixmap_private(back_priv->pixmap);
 	intel_set_pixmap_private(front_priv->pixmap, back_intel);
-	intel_set_pixmap_private(back_priv->pixmap, front_intel); /* should be screen */
+	intel_set_pixmap_private(back_priv->pixmap, front_intel);
 
-	/* Do we need to update the Screen? */
 	screen = draw->pScreen;
 	intel = intel_get_screen_private(xf86Screens[screen->myNum]);
-	if (front_intel->bo == intel->front_buffer) {
-	    dri_bo_unreference (intel->front_buffer);
-	    intel->front_buffer = back_intel->bo;
-	    dri_bo_reference (intel->front_buffer);
-	    intel_set_pixmap_private(screen->GetScreenPixmap(screen),
-				     back_intel);
-	    back_intel->busy = 1;
-	    front_intel->busy = -1;
-	}
+
+	dri_bo_unreference (intel->front_buffer);
+	intel->front_buffer = back_intel->bo;
+	dri_bo_reference (intel->front_buffer);
+
+	intel_set_pixmap_private(screen->GetScreenPixmap(screen), back_intel);
+	back_intel->busy = 1;
+	front_intel->busy = -1;
 }
 
 /*
@@ -782,47 +786,79 @@ I830DRI2ExchangeBuffers(DrawablePtr draw, DRI2BufferPtr front,
  */
 static Bool
 I830DRI2ScheduleFlip(struct intel_screen_private *intel,
-		     ClientPtr client, DrawablePtr draw, DRI2BufferPtr front,
-		     DRI2BufferPtr back, DRI2SwapEventPtr func, void *data,
-		     unsigned int target_msc)
+		     DrawablePtr draw,
+		     DRI2FrameEventPtr info)
 {
-	I830DRI2BufferPrivatePtr back_priv;
-	DRI2FrameEventPtr flip_info;
-
-	/* Main crtc for this drawable shall finally deliver pageflip event. */
-	int ref_crtc_hw_id = I830DRI2DrawablePipe(draw);
-
-	flip_info = calloc(1, sizeof(DRI2FrameEventRec));
-	if (!flip_info)
-	    return FALSE;
-
-	flip_info->drawable_id = draw->id;
-	flip_info->client = client;
-	flip_info->type = DRI2_SWAP;
-	flip_info->event_complete = func;
-	flip_info->event_data = data;
-	flip_info->frame = target_msc;
-
-	if (!i830_dri2_add_frame_event(flip_info)) {
-	    free(flip_info);
-	    return FALSE;
+	I830DRI2BufferPrivatePtr priv = info->back->driverPrivate;
+	drm_intel_bo *new_back, *old_back;
+
+	if (!intel->use_triple_buffer) {
+		if (!intel_do_pageflip(intel,
+				       intel_get_pixmap_bo(priv->pixmap),
+				       info, info->pipe))
+			return FALSE;
+
+		info->type = DRI2_SWAP;
+		I830DRI2ExchangeBuffers(draw, info->front, info->back);
+		return TRUE;
 	}
 
-	/* Page flip the full screen buffer */
-	back_priv = back->driverPrivate;
-	if (intel_do_pageflip(intel,
-			      intel_get_pixmap_bo(back_priv->pixmap),
-			      flip_info, ref_crtc_hw_id))
+	if (intel->pending_flip[info->pipe]) {
+		assert(intel->pending_flip[info->pipe]->chain == NULL);
+		intel->pending_flip[info->pipe]->chain = info;
 		return TRUE;
+	}
 
-	i830_dri2_del_frame_event(flip_info);
-	free(flip_info);
-	return FALSE;
+	if (intel->back_buffer == NULL) {
+		new_back = drm_intel_bo_alloc(intel->bufmgr, "front buffer",
+					      intel->front_buffer->size, 0);
+		if (new_back == NULL)
+			return FALSE;
+
+		if (intel->front_tiling != I915_TILING_NONE) {
+			uint32_t tiling = intel->front_tiling;
+			drm_intel_bo_set_tiling(new_back, &tiling, intel->front_pitch);
+			if (tiling != intel->front_tiling) {
+				drm_intel_bo_unreference(new_back);
+				return FALSE;
+			}
+		}
+
+		drm_intel_bo_disable_reuse(new_back);
+	} else {
+		new_back = intel->back_buffer;
+		intel->back_buffer = NULL;
+	}
+
+	old_back = intel_get_pixmap_bo(priv->pixmap);
+	if (!intel_do_pageflip(intel, old_back, info, info->pipe)) {
+		intel->back_buffer = new_back;
+		return FALSE;
+	}
+	info->type = DRI2_SWAP_CHAIN;
+	intel->pending_flip[info->pipe] = info;
+
+	/* Exchange the current front-buffer with the fresh bo */
+	intel->back_buffer = intel->front_buffer;
+	drm_intel_bo_reference(intel->back_buffer);
+
+	priv = info->front->driverPrivate;
+	intel_set_pixmap_bo(priv->pixmap, new_back);
+	dri_bo_flink(new_back, &info->front->name);
+
+	/* Then flip DRI2 pointers and update the screen pixmap */
+	I830DRI2ExchangeBuffers(draw, info->front, info->back);
+	DRI2SwapComplete(info->client, draw, 0, 0, 0,
+			 DRI2_EXCHANGE_COMPLETE,
+			 info->event_complete,
+			 info->event_data);
+	return TRUE;
 }
 
 static Bool
-can_exchange(DRI2BufferPtr front, DRI2BufferPtr back)
+can_exchange(DrawablePtr drawable, DRI2BufferPtr front, DRI2BufferPtr back)
 {
+	struct intel_screen_private *intel = intel_get_screen_private(xf86Screens[drawable->pScreen->myNum]);
 	I830DRI2BufferPrivatePtr front_priv = front->driverPrivate;
 	I830DRI2BufferPrivatePtr back_priv = back->driverPrivate;
 	PixmapPtr front_pixmap = front_priv->pixmap;
@@ -830,6 +866,18 @@ can_exchange(DRI2BufferPtr front, DRI2BufferPtr back)
 	struct intel_pixmap *front_intel = intel_get_pixmap_private(front_pixmap);
 	struct intel_pixmap *back_intel = intel_get_pixmap_private(back_pixmap);
 
+	if (drawable == NULL)
+		return FALSE;
+
+	if (!DRI2CanFlip(drawable))
+		return FALSE;
+
+	if (intel->shadow_present)
+		return FALSE;
+
+	if (!intel->use_pageflipping)
+		return FALSE;
+
 	if (front_pixmap->drawable.width != back_pixmap->drawable.width)
 		return FALSE;
 
@@ -855,10 +903,8 @@ can_exchange(DRI2BufferPtr front, DRI2BufferPtr back)
 void I830DRI2FrameEventHandler(unsigned int frame, unsigned int tv_sec,
 			       unsigned int tv_usec, DRI2FrameEventPtr swap_info)
 {
+	intel_screen_private *intel = swap_info->intel;
 	DrawablePtr drawable;
-	ScreenPtr screen;
-	ScrnInfoPtr scrn;
-	intel_screen_private *intel;
 	int status;
 
 	if (!swap_info->drawable_id)
@@ -867,56 +913,33 @@ void I830DRI2FrameEventHandler(unsigned int frame, unsigned int tv_sec,
 		status = dixLookupDrawable(&drawable, swap_info->drawable_id, serverClient,
 					   M_ANY, DixWriteAccess);
 	if (status != Success) {
-		i830_dri2_del_frame_event(swap_info);
-		I830DRI2DestroyBuffer(NULL, swap_info->front);
-		I830DRI2DestroyBuffer(NULL, swap_info->back);
-		free(swap_info);
+		i830_dri2_del_frame_event(NULL, swap_info);
 		return;
 	}
 
-	screen = drawable->pScreen;
-	scrn = xf86Screens[screen->myNum];
-	intel = intel_get_screen_private(scrn);
 
 	switch (swap_info->type) {
 	case DRI2_FLIP:
 		/* If we can still flip... */
-		if (DRI2CanFlip(drawable) && !intel->shadow_present &&
-		    intel->use_pageflipping &&
-		    can_exchange(swap_info->front, swap_info->back) &&
-		    I830DRI2ScheduleFlip(intel,
-					 swap_info->client, drawable, swap_info->front,
-					 swap_info->back, swap_info->event_complete,
-					 swap_info->event_data, swap_info->frame)) {
-			I830DRI2ExchangeBuffers(drawable,
-						swap_info->front, swap_info->back);
-			break;
-		}
+		if (can_exchange(drawable, swap_info->front, swap_info->back) &&
+		    I830DRI2ScheduleFlip(intel, drawable, swap_info))
+			return;
+
 		/* else fall through to exchange/blit */
 	case DRI2_SWAP: {
-		int swap_type;
-
-		if (DRI2CanExchange(drawable) && can_exchange(swap_info->front,
-							      swap_info->back)) {
-			I830DRI2ExchangeBuffers(drawable,
-						swap_info->front, swap_info->back);
-			swap_type = DRI2_EXCHANGE_COMPLETE;
-		} else {
-			BoxRec	    box;
-			RegionRec	    region;
-
-			box.x1 = 0;
-			box.y1 = 0;
-			box.x2 = drawable->width;
-			box.y2 = drawable->height;
-			REGION_INIT(pScreen, &region, &box, 0);
-
-			I830DRI2CopyRegion(drawable,
-					   &region, swap_info->front, swap_info->back);
-			swap_type = DRI2_BLIT_COMPLETE;
-		}
+		BoxRec box;
+		RegionRec region;
+
+		box.x1 = 0;
+		box.y1 = 0;
+		box.x2 = drawable->width;
+		box.y2 = drawable->height;
+		REGION_INIT(pScreen, &region, &box, 0);
+
+		I830DRI2CopyRegion(drawable,
+				   &region, swap_info->front, swap_info->back);
 		DRI2SwapComplete(swap_info->client, drawable, frame, tv_sec, tv_usec,
-				 swap_type,
+				 DRI2_BLIT_COMPLETE,
 				 swap_info->client ? swap_info->event_complete : NULL,
 				 swap_info->event_data);
 		break;
@@ -927,43 +950,34 @@ void I830DRI2FrameEventHandler(unsigned int frame, unsigned int tv_sec,
 					    frame, tv_sec, tv_usec);
 		break;
 	default:
-		xf86DrvMsg(scrn->scrnIndex, X_WARNING,
+		xf86DrvMsg(intel->scrn->scrnIndex, X_WARNING,
 			   "%s: unknown vblank event received\n", __func__);
 		/* Unknown type */
 		break;
 	}
 
-	i830_dri2_del_frame_event(swap_info);
-	I830DRI2DestroyBuffer(drawable, swap_info->front);
-	I830DRI2DestroyBuffer(drawable, swap_info->back);
-	free(swap_info);
+	i830_dri2_del_frame_event(drawable, swap_info);
 }
 
 void I830DRI2FlipEventHandler(unsigned int frame, unsigned int tv_sec,
 			      unsigned int tv_usec, DRI2FrameEventPtr flip_info)
 {
+	struct intel_screen_private *intel = flip_info->intel;
 	DrawablePtr drawable;
-	ScreenPtr screen;
-	ScrnInfoPtr scrn;
-	int status;
+	DRI2FrameEventPtr chain;
 
-	if (!flip_info->drawable_id)
-		status = BadDrawable;
-	else
-		status = dixLookupDrawable(&drawable, flip_info->drawable_id, serverClient,
-					   M_ANY, DixWriteAccess);
-	if (status != Success) {
-		i830_dri2_del_frame_event(flip_info);
-		free(flip_info);
-		return;
-	}
+	drawable = NULL;
+	if (flip_info->drawable_id)
+		dixLookupDrawable(&drawable, flip_info->drawable_id, serverClient,
+				  M_ANY, DixWriteAccess);
 
-	screen = drawable->pScreen;
-	scrn = xf86Screens[screen->myNum];
 
 	/* We assume our flips arrive in order, so we don't check the frame */
 	switch (flip_info->type) {
 	case DRI2_SWAP:
+		if (!drawable)
+			break;
+
 		/* Check for too small vblank count of pageflip completion, taking wraparound
 		 * into account. This usually means some defective kms pageflip completion,
 		 * causing wrong (msc, ust) return values and possible visual corruption.
@@ -975,7 +989,7 @@ void I830DRI2FlipEventHandler(unsigned int frame, unsigned int tv_sec,
 			 * kernels, so make it quieter.
 			 */
 			if (limit) {
-				xf86DrvMsg(scrn->scrnIndex, X_WARNING,
+				xf86DrvMsg(intel->scrn->scrnIndex, X_WARNING,
 					   "%s: Pageflip completion has impossible msc %d < target_msc %d\n",
 					   __func__, frame, flip_info->frame);
 				limit--;
@@ -988,16 +1002,52 @@ void I830DRI2FlipEventHandler(unsigned int frame, unsigned int tv_sec,
 		DRI2SwapComplete(flip_info->client, drawable, frame, tv_sec, tv_usec,
 				 DRI2_FLIP_COMPLETE, flip_info->client ? flip_info->event_complete : NULL,
 				 flip_info->event_data);
-	break;
+		break;
+
+	case DRI2_SWAP_CHAIN:
+		assert(intel->pending_flip[flip_info->pipe] == flip_info);
+		intel->pending_flip[flip_info->pipe] = NULL;
+
+		chain = flip_info->chain;
+		if (chain) {
+			DrawablePtr chain_drawable = NULL;
+			if (chain->drawable_id)
+				 dixLookupDrawable(&chain_drawable,
+						   chain->drawable_id,
+						   serverClient,
+						   M_ANY, DixWriteAccess);
+			if (chain_drawable == NULL) {
+				i830_dri2_del_frame_event(chain_drawable, chain);
+			} else if (!can_exchange(chain_drawable, chain->front, chain->back) ||
+				   !I830DRI2ScheduleFlip(intel, chain_drawable, chain)) {
+				BoxRec box;
+				RegionRec region;
+
+				box.x1 = 0;
+				box.y1 = 0;
+				box.x2 = chain_drawable->width;
+				box.y2 = chain_drawable->height;
+				REGION_INIT(pScreen, &region, &box, 0);
+
+				I830DRI2CopyRegion(chain_drawable, &region,
+						   chain->front, chain->back);
+				DRI2SwapComplete(chain->client, chain_drawable, frame, tv_sec, tv_usec,
+						 DRI2_BLIT_COMPLETE,
+						 chain->client ? chain->event_complete : NULL,
+						 chain->event_data);
+				i830_dri2_del_frame_event(chain_drawable, chain);
+			}
+		}
+		break;
+
 	default:
-		xf86DrvMsg(scrn->scrnIndex, X_WARNING,
+		xf86DrvMsg(intel->scrn->scrnIndex, X_WARNING,
 			   "%s: unknown vblank event received\n", __func__);
 		/* Unknown type */
 		break;
 	}
 
-	i830_dri2_del_frame_event(flip_info);
-	free(flip_info);
+	i830_dri2_del_frame_event(drawable, flip_info);
 }
 
 /*
@@ -1050,12 +1100,14 @@ I830DRI2ScheduleSwap(ClientPtr client, DrawablePtr draw, DRI2BufferPtr front,
 	if (!swap_info)
 	    goto blit_fallback;
 
+	swap_info->intel = intel;
 	swap_info->drawable_id = draw->id;
 	swap_info->client = client;
 	swap_info->event_complete = func;
 	swap_info->event_data = data;
 	swap_info->front = front;
 	swap_info->back = back;
+	swap_info->pipe = I830DRI2DrawablePipe(draw);
 
 	if (!i830_dri2_add_frame_event(swap_info)) {
 	    free(swap_info);
@@ -1082,10 +1134,7 @@ I830DRI2ScheduleSwap(ClientPtr client, DrawablePtr draw, DRI2BufferPtr front,
 	current_msc = vbl.reply.sequence;
 
 	/* Flips need to be submitted one frame before */
-	if (intel->use_pageflipping &&
-	    !intel->shadow_present &&
-	    DRI2CanFlip(draw) &&
-	    can_exchange(front, back)) {
+	if (can_exchange(draw, front, back)) {
 	    swap_type = DRI2_FLIP;
 	    flip = 1;
 	}
@@ -1105,6 +1154,9 @@ I830DRI2ScheduleSwap(ClientPtr client, DrawablePtr draw, DRI2BufferPtr front,
 	 * the swap.
 	 */
 	if (divisor == 0 || current_msc < *target_msc) {
+		if (flip && I830DRI2ScheduleFlip(intel, draw, swap_info))
+			return TRUE;
+
 		vbl.request.type =  DRM_VBLANK_ABSOLUTE | DRM_VBLANK_EVENT;
 		if (pipe > 0)
 			vbl.request.type |= DRM_VBLANK_SECONDARY;
@@ -1197,12 +1249,8 @@ blit_fallback:
 	I830DRI2CopyRegion(draw, &region, front, back);
 
 	DRI2SwapComplete(client, draw, 0, 0, 0, DRI2_BLIT_COMPLETE, func, data);
-	if (swap_info) {
-	    i830_dri2_del_frame_event(swap_info);
-	    I830DRI2DestroyBuffer(draw, swap_info->front);
-	    I830DRI2DestroyBuffer(draw, swap_info->back);
-	    free(swap_info);
-	}
+	if (swap_info)
+	    i830_dri2_del_frame_event(draw, swap_info);
 	*target_msc = 0; /* offscreen, so zero out target vblank count */
 	return TRUE;
 }
@@ -1283,6 +1331,7 @@ I830DRI2ScheduleWaitMSC(ClientPtr client, DrawablePtr draw, CARD64 target_msc,
 	if (!wait_info)
 		goto out_complete;
 
+	wait_info->intel = intel;
 	wait_info->drawable_id = draw->id;
 	wait_info->client = client;
 	wait_info->type = DRI2_WAITMSC;