On 23/04/2018 19:08, Chris Wilson wrote:
In commit 9b6586ae9f6b ("drm/i915: Keep a global seqno per-engine"), we
moved from a global inflight counter to per-engine counters in the
hope that will be easy to run concurrently in future. However, with the
advent of the desire to move requests between engines, we do need a
global counter to preserve the semantics that no engine wraps in the
middle of a submit. (Although this semantic is now only required for gen7
semaphore support, which only supports greater-then comparisons!)
v2: Keep a global counter of all requests ever submitted and force the
reset when it wraps.
References: 9b6586ae9f6b ("drm/i915: Keep a global seqno per-engine")
Signed-off-by: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx>
Cc: Tvrtko Ursulin <tvrtko.ursulin@xxxxxxxxx>
---
drivers/gpu/drm/i915/i915_debugfs.c | 5 ++--
drivers/gpu/drm/i915/i915_drv.h | 1 +
drivers/gpu/drm/i915/i915_gem_timeline.h | 6 -----
drivers/gpu/drm/i915/i915_request.c | 33 ++++++++++++------------
drivers/gpu/drm/i915/intel_engine_cs.c | 5 ++--
5 files changed, 22 insertions(+), 28 deletions(-)
diff --git a/drivers/gpu/drm/i915/i915_debugfs.c b/drivers/gpu/drm/i915/i915_debugfs.c
index 2f05f5262bba..547e97102b85 100644
--- a/drivers/gpu/drm/i915/i915_debugfs.c
+++ b/drivers/gpu/drm/i915/i915_debugfs.c
@@ -1340,10 +1340,9 @@ static int i915_hangcheck_info(struct seq_file *m, void *unused)
struct rb_node *rb;
seq_printf(m, "%s:\n", engine->name);
- seq_printf(m, "\tseqno = %x [current %x, last %x], inflight %d\n",
+ seq_printf(m, "\tseqno = %x [current %x, last %x]\n",
engine->hangcheck.seqno, seqno[id],
- intel_engine_last_submit(engine),
- engine->timeline->inflight_seqnos);
+ intel_engine_last_submit(engine));
seq_printf(m, "\twaiters? %s, fake irq active? %s, stalled? %s\n",
yesno(intel_engine_has_waiter(engine)),
yesno(test_bit(engine->id,
diff --git a/drivers/gpu/drm/i915/i915_drv.h b/drivers/gpu/drm/i915/i915_drv.h
index 8444ca8d5aa3..8fd9fb6efba5 100644
--- a/drivers/gpu/drm/i915/i915_drv.h
+++ b/drivers/gpu/drm/i915/i915_drv.h
@@ -2061,6 +2061,7 @@ struct drm_i915_private {
struct list_head timelines;
struct i915_gem_timeline global_timeline;
u32 active_requests;
+ u32 request_serial;
/**
* Is the GPU currently considered idle, or busy executing
diff --git a/drivers/gpu/drm/i915/i915_gem_timeline.h b/drivers/gpu/drm/i915/i915_gem_timeline.h
index 33e01bf6aa36..6e82119e2cd8 100644
--- a/drivers/gpu/drm/i915/i915_gem_timeline.h
+++ b/drivers/gpu/drm/i915/i915_gem_timeline.h
@@ -37,12 +37,6 @@ struct intel_timeline {
u64 fence_context;
u32 seqno;
- /**
- * Count of outstanding requests, from the time they are constructed
- * to the moment they are retired. Loosely coupled to hardware.
- */
- u32 inflight_seqnos;
-
spinlock_t lock;
/**
diff --git a/drivers/gpu/drm/i915/i915_request.c b/drivers/gpu/drm/i915/i915_request.c
index b692a9f7c357..f3d04f0ab21c 100644
--- a/drivers/gpu/drm/i915/i915_request.c
+++ b/drivers/gpu/drm/i915/i915_request.c
@@ -241,6 +241,7 @@ static int reset_all_global_seqno(struct drm_i915_private *i915, u32 seqno)
sizeof(timeline->engine[id].global_sync));
}
+ i915->gt.request_serial = seqno;
return 0;
}
@@ -257,18 +258,22 @@ int i915_gem_set_global_seqno(struct drm_device *dev, u32 seqno)
return reset_all_global_seqno(i915, seqno - 1);
}
-static int reserve_engine(struct intel_engine_cs *engine)
+static int reserve_gt(struct drm_i915_private *i915)
{
- struct drm_i915_private *i915 = engine->i915;
- u32 active = ++engine->timeline->inflight_seqnos;
- u32 seqno = engine->timeline->seqno;
int ret;
- /* Reservation is fine until we need to wrap around */
- if (unlikely(add_overflows(seqno, active))) {
+ /*
+ * Reservation is fine until we may need to wrap around
+ *
+ * By incrementing the serial for every request, we know that no
+ * individual engine may exceed that serial (as each is reset to 0
+ * on any wrap). This protects even the most pessimistic of migrations
+ * of every request from all engines onto just one.
+ */
I didn't really figure out what was wrong with v1? Neither could handle
more than four billion of simultaneously active requests - but I thought
that should not concern us. :)
I don't quite get wrapping based on otherwise unused counter.
v1 made sense to wrap then any engine timeline couldn't handle all
active requests without wrapping.
+ if (unlikely(++i915->gt.request_serial == 0)) {
ret = reset_all_global_seqno(i915, 0);
if (ret) {
- engine->timeline->inflight_seqnos--;
+ i915->gt.request_serial--;
return ret;
}
}
@@ -279,15 +284,10 @@ static int reserve_engine(struct intel_engine_cs *engine)
return 0;
}
-static void unreserve_engine(struct intel_engine_cs *engine)
+static void unreserve_gt(struct drm_i915_private *i915)
{
- struct drm_i915_private *i915 = engine->i915;
-
if (!--i915->gt.active_requests)
i915_gem_park(i915);
-
- GEM_BUG_ON(!engine->timeline->inflight_seqnos);
- engine->timeline->inflight_seqnos--;
}
void i915_gem_retire_noop(struct i915_gem_active *active,
@@ -362,7 +362,6 @@ static void i915_request_retire(struct i915_request *request)
list_del_init(&request->link);
spin_unlock_irq(&engine->timeline->lock);
- unreserve_engine(request->engine);
advance_ring(request);
free_capture_list(request);
@@ -424,6 +423,8 @@ static void i915_request_retire(struct i915_request *request)
}
spin_unlock_irq(&request->lock);
+ unreserve_gt(request->i915);
+
i915_sched_node_fini(request->i915, &request->sched);
i915_request_put(request);
}
@@ -642,7 +643,7 @@ i915_request_alloc(struct intel_engine_cs *engine, struct i915_gem_context *ctx)
return ERR_CAST(ring);
GEM_BUG_ON(!ring);
- ret = reserve_engine(engine);
+ ret = reserve_gt(i915);
Maybe more descriptive name? reserve_gt_global_seqno?
if (ret)
goto err_unpin;
@@ -784,7 +785,7 @@ i915_request_alloc(struct intel_engine_cs *engine, struct i915_gem_context *ctx)
kmem_cache_free(i915->requests, rq);
err_unreserve:
- unreserve_engine(engine);
+ unreserve_gt(i915);
err_unpin:
engine->context_unpin(engine, ctx);
return ERR_PTR(ret);
diff --git a/drivers/gpu/drm/i915/intel_engine_cs.c b/drivers/gpu/drm/i915/intel_engine_cs.c
index be608f7111f5..a55a849b81b6 100644
--- a/drivers/gpu/drm/i915/intel_engine_cs.c
+++ b/drivers/gpu/drm/i915/intel_engine_cs.c
@@ -1318,12 +1318,11 @@ void intel_engine_dump(struct intel_engine_cs *engine,
if (i915_terminally_wedged(&engine->i915->gpu_error))
drm_printf(m, "*** WEDGED ***\n");
- drm_printf(m, "\tcurrent seqno %x, last %x, hangcheck %x [%d ms], inflight %d\n",
+ drm_printf(m, "\tcurrent seqno %x, last %x, hangcheck %x [%d ms]\n",
intel_engine_get_seqno(engine),
intel_engine_last_submit(engine),
engine->hangcheck.seqno,
- jiffies_to_msecs(jiffies - engine->hangcheck.action_timestamp),
- engine->timeline->inflight_seqnos);
+ jiffies_to_msecs(jiffies - engine->hangcheck.action_timestamp));
drm_printf(m, "\tReset count: %d (global %d)\n",
i915_reset_engine_count(error, engine),
i915_reset_count(error));
Regards,
Tvrtko
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