[PATCH] drm/xe: Do not preempt fence signaling CS instructions

[Matthew Brost <matthew.brost@intel.com>]

If a batch buffer is complete, it makes little sense to preempt the
fence signaling instructions in the ring, as the largest portion of the
work (the batch buffer) is already done and fence signaling consists of
only a few instructions. If these instructions are preempted, the GuC
would need to perform a context switch just to signal the fence, which
is costly and delays fence signaling. Avoid this scenario by disabling
preemption immediately after the BB start instruction and re-enabling it
after executing the fence signaling instructions.

Fixes: dd08ebf6c352 ("drm/xe: Introduce a new DRM driver for Intel GPUs")
Cc: Daniele Ceraolo Spurio <daniele.ceraolospurio@intel.com>
Cc: Carlos Santa <carlos.santa@intel.com>
Signed-off-by: Matthew Brost <matthew.brost@intel.com>
---
 drivers/gpu/drm/xe/xe_ring_ops.c | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/drivers/gpu/drm/xe/xe_ring_ops.c b/drivers/gpu/drm/xe/xe_ring_ops.c
index a1fd99f2d539..cd645ee400b9 100644
--- a/drivers/gpu/drm/xe/xe_ring_ops.c
+++ b/drivers/gpu/drm/xe/xe_ring_ops.c
@@ -282,6 +282,9 @@ static void __emit_job_gen12_simple(struct xe_sched_job *job, struct xe_lrc *lrc
 
 	i = emit_bb_start(batch_addr, ppgtt_flag, dw, i);
 
+	/* Don't preempt fence signaling */
+	dw[i++] = MI_ARB_ON_OFF | MI_ARB_DISABLE;
+
 	if (job->user_fence.used) {
 		i = emit_flush_dw(dw, i);
 		i = emit_store_imm_ppgtt_posted(job->user_fence.addr,
@@ -347,6 +350,9 @@ static void __emit_job_gen12_video(struct xe_sched_job *job, struct xe_lrc *lrc,
 
 	i = emit_bb_start(batch_addr, ppgtt_flag, dw, i);
 
+	/* Don't preempt fence signaling */
+	dw[i++] = MI_ARB_ON_OFF | MI_ARB_DISABLE;
+
 	if (job->user_fence.used) {
 		i = emit_flush_dw(dw, i);
 		i = emit_store_imm_ppgtt_posted(job->user_fence.addr,
@@ -399,6 +405,9 @@ static void __emit_job_gen12_render_compute(struct xe_sched_job *job,
 
 	i = emit_bb_start(batch_addr, ppgtt_flag, dw, i);
 
+	/* Don't preempt fence signaling */
+	dw[i++] = MI_ARB_ON_OFF | MI_ARB_DISABLE;
+
 	i = emit_render_cache_flush(job, dw, i);
 
 	if (job->user_fence.used)
-- 
2.34.1