Revert "intel: use throttle ioctl for throttling"

This reverts commit 50ade6ea69.

Fixes jerky rendering again on apps that don't block on the GPU per
frame and are GPU bound (e.g. 3DMMES on Ironlake).  The whole point of
this complicated throttle scheme is to wait on frame n-1 to have
started rendering before starting frame n's rendering.  Otherwise, the
GPU-bound app will race ahead and call the GL to draw many
nearly-identical frames, then >0ms later get stuck waiting for them
(all dispatched at about the same time) to retire, then render a new
batch of nearly-identical frames.

src/mesa/drivers/dri/intel/intel_batchbuffer.c

@@ -128,6 +128,11 @@ _intel_batchbuffer_flush(struct intel_context *intel,
    if (intel->batch.used == 0)
       return;
 
+   if (intel->first_post_swapbuffers_batch == NULL) {
+      intel->first_post_swapbuffers_batch = intel->batch.bo;
+      drm_intel_bo_reference(intel->first_post_swapbuffers_batch);
+   }
+
    if (unlikely(INTEL_DEBUG & DEBUG_BATCH))
       fprintf(stderr, "%s:%d: Batchbuffer flush with %db used\n", file, line,
 	      4*intel->batch.used);

src/mesa/drivers/dri/intel/intel_context.c

@@ -466,9 +466,11 @@ intel_prepare_render(struct intel_context *intel)
     * the swap, and getting our hands on that doesn't seem worth it,
     * so we just us the first batch we emitted after the last swap.
     */
-   if (intel->need_throttle) {
-       drmCommandNone(intel->driFd, DRM_I915_GEM_THROTTLE);
-       intel->need_throttle = GL_FALSE;
+   if (intel->need_throttle && intel->first_post_swapbuffers_batch) {
+      drm_intel_bo_wait_rendering(intel->first_post_swapbuffers_batch);
+      drm_intel_bo_unreference(intel->first_post_swapbuffers_batch);
+      intel->first_post_swapbuffers_batch = NULL;
+      intel->need_throttle = GL_FALSE;
    }
 }
 
@@ -938,6 +940,8 @@ intelDestroyContext(__DRIcontext * driContextPriv)
       intel->prim.vb = NULL;
       drm_intel_bo_unreference(intel->prim.vb_bo);
       intel->prim.vb_bo = NULL;
+      drm_intel_bo_unreference(intel->first_post_swapbuffers_batch);
+      intel->first_post_swapbuffers_batch = NULL;
 
       driDestroyOptionCache(&intel->optionCache);
 

src/mesa/drivers/dri/intel/intel_context.h

@@ -182,6 +182,7 @@ struct intel_context
       bool is_blit;
    } batch;
 
+   drm_intel_bo *first_post_swapbuffers_batch;
    GLboolean need_throttle;
    GLboolean no_batch_wrap;