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Commit 19f8fb27 authored by Chris Wilson's avatar Chris Wilson Committed by Greg Kroah-Hartman
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drm/i915/execlists: Always force a context reload when rewinding RING_TAIL 



commit b1339ecac661e1cf3e1dc78ac56bff3aeeaeb92c upstream.

If we rewind the RING_TAIL on a context, due to a preemption event, we
must force the context restore for the RING_TAIL update to be properly
handled. Rather than note which preemption events may cause us to rewind
the tail, compare the new request's tail with the previously submitted
RING_TAIL, as it turns out that timeslicing was causing unexpected
rewinds.

   <idle>-0       0d.s2 1280851190us : __execlists_submission_tasklet: 0000:00:02.0 rcs0: expired last=130:4698, prio=3, hint=3
   <idle>-0       0d.s2 1280851192us : __i915_request_unsubmit: 0000:00:02.0 rcs0: fence 66:119966, current 119964
   <idle>-0       0d.s2 1280851195us : __i915_request_unsubmit: 0000:00:02.0 rcs0: fence 130:4698, current 4695
   <idle>-0       0d.s2 1280851198us : __i915_request_unsubmit: 0000:00:02.0 rcs0: fence 130:4696, current 4695
^----  Note we unwind 2 requests from the same context

   <idle>-0       0d.s2 1280851208us : __i915_request_submit: 0000:00:02.0 rcs0: fence 130:4696, current 4695
   <idle>-0       0d.s2 1280851213us : __i915_request_submit: 0000:00:02.0 rcs0: fence 134:1508, current 1506
^---- But to apply the new timeslice, we have to replay the first request
      before the new client can start -- the unexpected RING_TAIL rewind

   <idle>-0       0d.s2 1280851219us : trace_ports: 0000:00:02.0 rcs0: submit { 130:4696*, 134:1508 }
 synmark2-5425    2..s. 1280851239us : process_csb: 0000:00:02.0 rcs0: cs-irq head=5, tail=0
 synmark2-5425    2..s. 1280851240us : process_csb: 0000:00:02.0 rcs0: csb[0]: status=0x00008002:0x00000000
^---- Preemption event for the ELSP update; note the lite-restore

 synmark2-5425    2..s. 1280851243us : trace_ports: 0000:00:02.0 rcs0: preempted { 130:4698, 66:119966 }
 synmark2-5425    2..s. 1280851246us : trace_ports: 0000:00:02.0 rcs0: promote { 130:4696*, 134:1508 }
 synmark2-5425    2.... 1280851462us : __i915_request_commit: 0000:00:02.0 rcs0: fence 130:4700, current 4695
 synmark2-5425    2.... 1280852111us : __i915_request_commit: 0000:00:02.0 rcs0: fence 130:4702, current 4695
 synmark2-5425    2.Ns1 1280852296us : process_csb: 0000:00:02.0 rcs0: cs-irq head=0, tail=2
 synmark2-5425    2.Ns1 1280852297us : process_csb: 0000:00:02.0 rcs0: csb[1]: status=0x00000814:0x00000000
 synmark2-5425    2.Ns1 1280852299us : trace_ports: 0000:00:02.0 rcs0: completed { 130:4696!, 134:1508 }
 synmark2-5425    2.Ns1 1280852301us : process_csb: 0000:00:02.0 rcs0: csb[2]: status=0x00000818:0x00000040
 synmark2-5425    2.Ns1 1280852302us : trace_ports: 0000:00:02.0 rcs0: completed { 134:1508, 0:0 }
 synmark2-5425    2.Ns1 1280852313us : process_csb: process_csb:2336 GEM_BUG_ON(!i915_request_completed(*execlists->active) && !reset_in_progress(execlists))

Fixes: 8ee36e04 ("drm/i915/execlists: Minimalistic timeslicing")
Referenecs: 82c69bf58650 ("drm/i915/gt: Detect if we miss WaIdleLiteRestore")
Signed-off-by: default avatarChris Wilson <chris@chris-wilson.co.uk>
Cc: Mika Kuoppala <mika.kuoppala@linux.intel.com>
Reviewed-by: default avatarMika Kuoppala <mika.kuoppala@linux.intel.com>
Cc: <stable@vger.kernel.org> # v5.4+
Link: https://patchwork.freedesktop.org/patch/msgid/20200207211452.2860634-1-chris@chris-wilson.co.uk


(cherry picked from commit 5ba32c7be81e53ea8a27190b0f6be98e6c6779af)
Signed-off-by: default avatarJani Nikula <jani.nikula@intel.com>
Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
parent 1e0175a1

drivers/gpu/drm/i915/gt/intel_engine.h

+8 −0
Original line number Diff line number Diff line
@@ -250,6 +250,14 @@ static inline u32 intel_ring_wrap(const struct intel_ring *ring, u32 pos) 
	return pos & (ring->size - 1);

}



static inline int intel_ring_direction(const struct intel_ring *ring,

				       u32 next, u32 prev)

{

	typecheck(typeof(ring->size), next);

	typecheck(typeof(ring->size), prev);

	return (next - prev) << ring->wrap;

}



static inline bool

intel_ring_offset_valid(const struct intel_ring *ring,

			unsigned int pos)

drivers/gpu/drm/i915/gt/intel_engine_types.h

+1 −0
Original line number Diff line number Diff line
@@ -107,6 +107,7 @@ struct intel_ring { 


	u32 space;

	u32 size;

	u32 wrap;

	u32 effective_size;

};

drivers/gpu/drm/i915/gt/intel_lrc.c

+8 −10
Original line number Diff line number Diff line
@@ -647,7 +647,7 @@ static u64 execlists_update_context(struct i915_request *rq) 
{

	struct intel_context *ce = rq->hw_context;

	u64 desc = ce->lrc_desc;

	u32 tail;

	u32 tail, prev;



	/*

	 * WaIdleLiteRestore:bdw,skl
@@ -660,9 +660,15 @@ static u64 execlists_update_context(struct i915_request *rq) 
	 * subsequent resubmissions (for lite restore). Should that fail us,

	 * and we try and submit the same tail again, force the context

	 * reload.

	 *

	 * If we need to return to a preempted context, we need to skip the

	 * lite-restore and force it to reload the RING_TAIL. Otherwise, the

	 * HW has a tendency to ignore us rewinding the TAIL to the end of

	 * an earlier request.

	 */

	tail = intel_ring_set_tail(rq->ring, rq->tail);

	if (unlikely(ce->lrc_reg_state[CTX_RING_TAIL + 1] == tail))

	prev = ce->lrc_reg_state[CTX_RING_TAIL + 1];

	if (unlikely(intel_ring_direction(rq->ring, tail, prev) <= 0))

		desc |= CTX_DESC_FORCE_RESTORE;

	ce->lrc_reg_state[CTX_RING_TAIL + 1] = tail;

	rq->tail = rq->wa_tail;
@@ -1110,14 +1116,6 @@ static void execlists_dequeue(struct intel_engine_cs *engine) 
			 */

			__unwind_incomplete_requests(engine);



			/*

			 * If we need to return to the preempted context, we

			 * need to skip the lite-restore and force it to

			 * reload the RING_TAIL. Otherwise, the HW has a

			 * tendency to ignore us rewinding the TAIL to the

			 * end of an earlier request.

			 */

			last->hw_context->lrc_desc |= CTX_DESC_FORCE_RESTORE;

			last = NULL;

		} else if (need_timeslice(engine, last) &&

			   !timer_pending(&engine->execlists.timer)) {

drivers/gpu/drm/i915/gt/intel_ringbuffer.c

+2 −0
Original line number Diff line number Diff line
@@ -1312,6 +1312,8 @@ intel_engine_create_ring(struct intel_engine_cs *engine, int size) 
	kref_init(&ring->ref);



	ring->size = size;

	ring->wrap = BITS_PER_TYPE(ring->size) - ilog2(size);



	/* Workaround an erratum on the i830 which causes a hang if

	 * the TAIL pointer points to within the last 2 cachelines

	 * of the buffer.