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: 8ee36e048c98 ("drm/i915/execlists: Minimalistic timeslicing")
Referenecs: 82c69bf58650 ("drm/i915/gt: Detect if we miss WaIdleLiteRestore")
Signed-off-by: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx>
Cc: Mika Kuoppala <mika.kuoppala@xxxxxxxxxxxxxxx>
Reviewed-by: Mika Kuoppala <mika.kuoppala@xxxxxxxxxxxxxxx>
Cc: <stable@xxxxxxxxxxxxxxx> # v5.4+
Link: https://patchwork.freedesktop.org/patch/msgid/20200207211452.2860634-1-chris@xxxxxxxxxxxxxxxxxx
(cherry picked from commit 5ba32c7be81e53ea8a27190b0f6be98e6c6779af)
---
drivers/gpu/drm/i915/gt/intel_lrc.c | 18 ++++++++----------
drivers/gpu/drm/i915/gt/intel_ring.c | 1 +
drivers/gpu/drm/i915/gt/intel_ring.h | 8 ++++++++
drivers/gpu/drm/i915/gt/intel_ring_types.h | 1 +
4 files changed, 18 insertions(+), 10 deletions(-)
diff --git a/drivers/gpu/drm/i915/gt/intel_lrc.c b/drivers/gpu/drm/i915/gt/intel_lrc.c
index cded952e7ddf1..742c08e79409d 100644
--- a/drivers/gpu/drm/i915/gt/intel_lrc.c
+++ b/drivers/gpu/drm/i915/gt/intel_lrc.c
@@ -1446,7 +1446,7 @@ static u64 execlists_update_context(struct i915_request *rq)
{
struct intel_context *ce = rq->context;
u64 desc = ce->lrc_desc;
- u32 tail;
+ u32 tail, prev;
/*
* WaIdleLiteRestore:bdw,skl
@@ -1459,9 +1459,15 @@ 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] == tail))
+ prev = ce->lrc_reg_state[CTX_RING_TAIL];
+ if (unlikely(intel_ring_direction(rq->ring, tail, prev) <= 0))
desc |= CTX_DESC_FORCE_RESTORE;
ce->lrc_reg_state[CTX_RING_TAIL] = tail;
rq->tail = rq->wa_tail;
@@ -1979,14 +1985,6 @@ 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->context->lrc_desc |= CTX_DESC_FORCE_RESTORE;
last = NULL;
} else if (need_timeslice(engine, last) &&
timer_expired(&engine->execlists.timer)) {
diff --git a/drivers/gpu/drm/i915/gt/intel_ring.c b/drivers/gpu/drm/i915/gt/intel_ring.c
index 374b28f13ca0b..6ff803f397c4d 100644
--- a/drivers/gpu/drm/i915/gt/intel_ring.c
+++ b/drivers/gpu/drm/i915/gt/intel_ring.c
@@ -145,6 +145,7 @@ 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
diff --git a/drivers/gpu/drm/i915/gt/intel_ring.h b/drivers/gpu/drm/i915/gt/intel_ring.h
index ea2839d9e0445..5bdce24994aa0 100644
--- a/drivers/gpu/drm/i915/gt/intel_ring.h
+++ b/drivers/gpu/drm/i915/gt/intel_ring.h
@@ -56,6 +56,14 @@ 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)
diff --git a/drivers/gpu/drm/i915/gt/intel_ring_types.h b/drivers/gpu/drm/i915/gt/intel_ring_types.h
index d9f17f38e0cce..3cd7fec7fd8d5 100644
--- a/drivers/gpu/drm/i915/gt/intel_ring_types.h
+++ b/drivers/gpu/drm/i915/gt/intel_ring_types.h
@@ -45,6 +45,7 @@ struct intel_ring {
u32 space;
u32 size;
+ u32 wrap;
u32 effective_size;
};
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