When we write to ELSP, it triggers a context preemption at the earliest
arbitration point (3DPRIMITIVE, some PIPECONTROLs, a few other
operations and the explicit MI_ARB_CHECK). If this is to the same
context, it triggers a LITE_RESTORE where the RING_TAIL is merely
updated (used currently to chain requests from the same context
together, avoiding bubbles). However, if it is to a different context, a
full context-switch is performed and it will start to execute the new
context saving the image of the old for later execution.
Previously we avoided preemption by only submitting a new context when
the old was idle. But now we wish embrace it, and if the new request has
a higher priority than the currently executing request, we write to the
ELSP regardless, thus triggering preemption, but we tell the GPU to
switch to our special preemption context (not the target). In the
context-switch interrupt handler, we know that the previous contexts
have finished execution and so can unwind all the incomplete requests
and compute the new highest priority request to execute.
It would be feasible to avoid the switch-to-idle intermediate by
programming the ELSP with the target context. The difficulty is in
tracking which request that should be whilst maintaining the dependency
change, the error comes in with coalesced requests. As we only track the
most recent request and its priority, we may run into the issue of being
tricked in preempting a high priority request that was followed by a
low priority request from the same context (e.g. for PI); worse still
that earlier request may be our own dependency and the order then broken
by preemption. By injecting the switch-to-idle and then recomputing the
priority queue, we avoid the issue with tracking in-flight coalesced
requests. Having tried the preempt-to-busy approach, and failed to find
a way around the coalesced priority issue, Michal's original proposal to
inject an idle context (based on handling GuC preemption) succeeds.
The current heuristic for deciding when to preempt are only if the new
request is of higher priority, and has the privileged priority of
greater than 0. Note that the scheduler remains unfair!
v2: Disable for gen8 (bdw/bsw) as we need additional w/a for GPGPU.
Since, the feature is now conditional and not always available when we
have a scheduler, make it known via the HAS_SCHEDULER GETPARAM (now a
capability mask).
Suggested-by: Michal Winiarski <michal.winiarski@xxxxxxxxx>
Signed-off-by: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx>
Cc: Michal Winiarski <michal.winiarski@xxxxxxxxx>
Cc: Tvrtko Ursulin <tvrtko.ursulin@xxxxxxxxx>
Cc: Arkadiusz Hiler <arkadiusz.hiler@xxxxxxxxx>
Cc: Mika Kuoppala <mika.kuoppala@xxxxxxxxx>
Cc: Ben Widawsky <benjamin.widawsky@xxxxxxxxx>
Cc: Zhenyu Wang <zhenyuw@xxxxxxxxxxxxxxx>
Cc: Zhi Wang <zhi.a.wang@xxxxxxxxx>
---
drivers/gpu/drm/i915/i915_drv.c | 9 ++-
drivers/gpu/drm/i915/i915_irq.c | 6 +-
drivers/gpu/drm/i915/i915_pci.c | 1 +
drivers/gpu/drm/i915/intel_lrc.c | 129 +++++++++++++++++++++++++-------
drivers/gpu/drm/i915/intel_ringbuffer.h | 2 +
5 files changed, 113 insertions(+), 34 deletions(-)
diff --git a/drivers/gpu/drm/i915/i915_drv.c b/drivers/gpu/drm/i915/i915_drv.c
index db3438ba92fd..d1949b40f419 100644
--- a/drivers/gpu/drm/i915/i915_drv.c
+++ b/drivers/gpu/drm/i915/i915_drv.c
@@ -368,9 +368,16 @@ static int i915_getparam(struct drm_device *dev, void *data,
break;
case I915_PARAM_HAS_SCHEDULER:
value = 0;
- if (dev_priv->engine[RCS] && dev_priv->engine[RCS]->schedule)
+ if (dev_priv->engine[RCS] && dev_priv->engine[RCS]->schedule) {
value |= I915_SCHEDULER_CAP_ENABLED;
+
+ if (INTEL_INFO(dev_priv)->has_logical_ring_preemption &&
+ i915_modparams.enable_execlists &&
+ !i915_modparams.enable_guc_submission)
+ value |= I915_SCHEDULER_CAP_PREEMPTION;
+ }
break;
+
case I915_PARAM_MMAP_VERSION:
/* Remember to bump this if the version changes! */
case I915_PARAM_HAS_GEM:
diff --git a/drivers/gpu/drm/i915/i915_irq.c b/drivers/gpu/drm/i915/i915_irq.c
index 0b7562135d1c..f4bc9ed560b1 100644
--- a/drivers/gpu/drm/i915/i915_irq.c
+++ b/drivers/gpu/drm/i915/i915_irq.c
@@ -1382,10 +1382,8 @@ gen8_cs_irq_handler(struct intel_engine_cs *engine, u32 iir, int test_shift)
bool tasklet = false;
if (iir & (GT_CONTEXT_SWITCH_INTERRUPT << test_shift)) {
- if (port_count(&execlists->port[0])) {
- __set_bit(ENGINE_IRQ_EXECLIST, &engine->irq_posted);
- tasklet = true;
- }
+ __set_bit(ENGINE_IRQ_EXECLIST, &engine->irq_posted);
+ tasklet = true;
}
if (iir & (GT_RENDER_USER_INTERRUPT << test_shift)) {
diff --git a/drivers/gpu/drm/i915/i915_pci.c b/drivers/gpu/drm/i915/i915_pci.c
index da60866b6628..931537df54f1 100644
--- a/drivers/gpu/drm/i915/i915_pci.c
+++ b/drivers/gpu/drm/i915/i915_pci.c
@@ -470,6 +470,7 @@ static const struct intel_device_info intel_skylake_gt4_info __initconst = {
.has_rc6 = 1, \
.has_dp_mst = 1, \
.has_logical_ring_contexts = 1, \
+ .has_logical_ring_preemption = 1, \
.has_guc = 1, \
.has_aliasing_ppgtt = 1, \
.has_full_ppgtt = 1, \
diff --git a/drivers/gpu/drm/i915/intel_lrc.c b/drivers/gpu/drm/i915/intel_lrc.c
index 7ac92a77aea8..9cdd55e9a9c0 100644
--- a/drivers/gpu/drm/i915/intel_lrc.c
+++ b/drivers/gpu/drm/i915/intel_lrc.c
@@ -208,8 +208,8 @@
/* Typical size of the average request (2 pipecontrols and a MI_BB) */
#define EXECLISTS_REQUEST_SIZE 64 /* bytes */
-
#define WA_TAIL_DWORDS 2
+#define PREEMPT_ID 0x1
static int execlists_context_deferred_alloc(struct i915_gem_context *ctx,
struct intel_engine_cs *engine);
@@ -489,26 +489,44 @@ static void port_assign(struct execlist_port *port,
port_set(port, port_pack(i915_gem_request_get(rq), port_count(port)));
}
+static void inject_preempt_context(struct intel_engine_cs *engine)
+{
+ struct intel_context *ce =
+ &engine->i915->preempt_context->engine[engine->id];
+ u32 __iomem *elsp =
+ engine->i915->regs + i915_mmio_reg_offset(RING_ELSP(engine));
+ unsigned int n;
+
+ GEM_BUG_ON(engine->i915->preempt_context->hw_id != PREEMPT_ID);
+
+ memset(ce->ring->vaddr + ce->ring->tail, 0, 8);
+ ce->ring->tail += 8;
+ ce->ring->tail &= (ce->ring->size - 1);
+ ce->lrc_reg_state[CTX_RING_TAIL+1] = ce->ring->tail;
+
+ for (n = execlists_num_ports(&engine->execlists); --n; ) {
+ writel(0, elsp);
+ writel(0, elsp);
+ }
+ writel(upper_32_bits(ce->lrc_desc), elsp);
+ writel(lower_32_bits(ce->lrc_desc), elsp);
+}
+
+static bool can_preempt(struct intel_engine_cs *engine)
+{
+ return INTEL_INFO(engine->i915)->has_logical_ring_preemption;
+}
+
static void execlists_dequeue(struct intel_engine_cs *engine)
{
- struct drm_i915_gem_request *last;
struct intel_engine_execlists * const execlists = &engine->execlists;
struct execlist_port *port = execlists->port;
const struct execlist_port * const last_port =
&execlists->port[execlists->port_mask];
+ struct drm_i915_gem_request *last = port_request(port);
struct rb_node *rb;
bool submit = false;
- last = port_request(port);
- if (last)
- /* WaIdleLiteRestore:bdw,skl
- * Apply the wa NOOPs to prevent ring:HEAD == req:TAIL
- * as we resubmit the request. See gen8_emit_breadcrumb()
- * for where we prepare the padding after the end of the
- * request.
- */
- last->tail = last->wa_tail;
-
/* Hardware submission is through 2 ports. Conceptually each port
* has a (RING_START, RING_HEAD, RING_TAIL) tuple. RING_START is
* static for a context, and unique to each, so we only execute
@@ -533,7 +551,45 @@ static void execlists_dequeue(struct intel_engine_cs *engine)
spin_lock_irq(&engine->timeline->lock);
rb = execlists->first;
GEM_BUG_ON(rb_first(&execlists->queue) != rb);
- while (rb) {
+ if (!rb)
+ goto unlock;
+
+ if (last) {
+ /*
+ * Don't resubmit or switch until all outstanding
+ * preemptions (lite-restore) are seen. Then we
+ * know the next preemption status we see corresponds
+ * to this ELSP update.
+ */
+ if (port_count(&port[0]) > 1)
+ goto unlock;
+
+ if (can_preempt(engine) &&
+ rb_entry(rb, struct i915_priolist, node)->priority >
+ max(last->priotree.priority, 0)) {
+ /*
+ * Switch to our empty preempt context so
+ * the state of the GPU is known (idle).
+ */
+ inject_preempt_context(engine);
+ execlists->preempt = true;
+ goto unlock;
+ } else {
+ if (port_count(&port[1]))
+ goto unlock;
+
+ /* WaIdleLiteRestore:bdw,skl
+ * Apply the wa NOOPs to prevent
+ * ring:HEAD == req:TAIL as we resubmit the
+ * request. See gen8_emit_breadcrumb() for
+ * where we prepare the padding after the
+ * end of the request.
+ */
+ last->tail = last->wa_tail;
+ }
+ }
+
+ do {
struct i915_priolist *p = rb_entry(rb, typeof(*p), node);
struct drm_i915_gem_request *rq, *rn;
@@ -596,11 +652,12 @@ static void execlists_dequeue(struct intel_engine_cs *engine)
INIT_LIST_HEAD(&p->requests);
if (p->priority != I915_PRIORITY_NORMAL)
kmem_cache_free(engine->i915->priorities, p);
- }
+ } while (rb);
done:
execlists->first = rb;
if (submit)
port_assign(port, last);
+unlock:
spin_unlock_irq(&engine->timeline->lock);
if (submit)
@@ -681,13 +738,6 @@ static void execlists_cancel_requests(struct intel_engine_cs *engine)
spin_unlock_irqrestore(&engine->timeline->lock, flags);
}
-static bool execlists_elsp_ready(const struct intel_engine_cs *engine)
-{
- const struct execlist_port *port = engine->execlists.port;
-
- return port_count(&port[0]) + port_count(&port[1]) < 2;
-}
-
/*
* Check the unread Context Status Buffers and manage the submission of new
* contexts to the ELSP accordingly.
@@ -696,7 +746,7 @@ static void intel_lrc_irq_handler(unsigned long data)
{
struct intel_engine_cs * const engine = (struct intel_engine_cs *)data;
struct intel_engine_execlists * const execlists = &engine->execlists;
- struct execlist_port *port = execlists->port;
+ struct execlist_port * const port = execlists->port;
struct drm_i915_private *dev_priv = engine->i915;
/* We can skip acquiring intel_runtime_pm_get() here as it was taken
@@ -781,6 +831,23 @@ static void intel_lrc_irq_handler(unsigned long data)
if (!(status & GEN8_CTX_STATUS_COMPLETED_MASK))
continue;
+ if (status & GEN8_CTX_STATUS_ACTIVE_IDLE &&
+ buf[2*head + 1] == PREEMPT_ID) {
+ execlist_cancel_port_requests(execlists);
+
+ spin_lock_irq(&engine->timeline->lock);
+ unwind_incomplete_requests(engine);
+ spin_unlock_irq(&engine->timeline->lock);
+
+ GEM_BUG_ON(!execlists->preempt);
+ execlists->preempt = false;
+ continue;
+ }
+
+ if (status & GEN8_CTX_STATUS_PREEMPTED &&
+ execlists->preempt)
+ continue;
+
/* Check the context/desc id for this event matches */
GEM_DEBUG_BUG_ON(buf[2 * head + 1] != port->context_id);
@@ -812,7 +879,7 @@ static void intel_lrc_irq_handler(unsigned long data)
}
}
- if (execlists_elsp_ready(engine))
+ if (!execlists->preempt)
execlists_dequeue(engine);
intel_uncore_forcewake_put(dev_priv, execlists->fw_domains);
@@ -825,7 +892,7 @@ static void insert_request(struct intel_engine_cs *engine,
struct i915_priolist *p = lookup_priolist(engine, pt, prio);
list_add_tail(&pt->link, &ptr_mask_bits(p, 1)->requests);
- if (ptr_unmask_bits(p, 1) && execlists_elsp_ready(engine))
+ if (ptr_unmask_bits(p, 1))
tasklet_hi_schedule(&engine->execlists.irq_tasklet);
}
@@ -953,8 +1020,6 @@ static void execlists_schedule(struct drm_i915_gem_request *request, int prio)
}
spin_unlock_irq(&engine->timeline->lock);
-
- /* XXX Do we need to preempt to make room for us and our deps? */
}
static struct intel_ring *
@@ -1150,6 +1215,8 @@ static u32 *gen8_init_indirectctx_bb(struct intel_engine_cs *engine, u32 *batch)
i915_ggtt_offset(engine->scratch) +
2 * CACHELINE_BYTES);
+ *batch++ = MI_ARB_ON_OFF | MI_ARB_ENABLE;
+
/* Pad to end of cacheline */
while ((unsigned long)batch % CACHELINE_BYTES)
*batch++ = MI_NOOP;
@@ -1165,6 +1232,8 @@ static u32 *gen8_init_indirectctx_bb(struct intel_engine_cs *engine, u32 *batch)
static u32 *gen9_init_indirectctx_bb(struct intel_engine_cs *engine, u32 *batch)
{
+ *batch++ = MI_ARB_ON_OFF | MI_ARB_DISABLE;
+
/* WaFlushCoherentL3CacheLinesAtContextSwitch:skl,bxt,glk */
batch = gen8_emit_flush_coherentl3_wa(engine, batch);
@@ -1210,6 +1279,8 @@ static u32 *gen9_init_indirectctx_bb(struct intel_engine_cs *engine, u32 *batch)
*batch++ = 0;
}
+ *batch++ = MI_ARB_ON_OFF | MI_ARB_ENABLE;
+
/* Pad to end of cacheline */
while ((unsigned long)batch % CACHELINE_BYTES)
*batch++ = MI_NOOP;
@@ -1363,6 +1434,7 @@ static int gen8_init_common_ring(struct intel_engine_cs *engine)
GT_CONTEXT_SWITCH_INTERRUPT << engine->irq_shift);
clear_bit(ENGINE_IRQ_EXECLIST, &engine->irq_posted);
execlists->csb_head = -1;
+ execlists->preempt = false;
/* After a GPU reset, we may have requests to replay */
if (!i915_modparams.enable_guc_submission && execlists->first)
@@ -1658,7 +1730,8 @@ static int gen8_emit_flush_render(struct drm_i915_gem_request *request,
*/
static void gen8_emit_wa_tail(struct drm_i915_gem_request *request, u32 *cs)
{
- *cs++ = MI_NOOP;
+ /* Ensure there's always at least one preemption point per-request. */
+ *cs++ = MI_ARB_CHECK;
*cs++ = MI_NOOP;
request->wa_tail = intel_ring_offset(request, cs);
}
@@ -1679,7 +1752,6 @@ static void gen8_emit_breadcrumb(struct drm_i915_gem_request *request, u32 *cs)
gen8_emit_wa_tail(request, cs);
}
-
static const int gen8_emit_breadcrumb_sz = 6 + WA_TAIL_DWORDS;
static void gen8_emit_breadcrumb_render(struct drm_i915_gem_request *request,
@@ -1707,7 +1779,6 @@ static void gen8_emit_breadcrumb_render(struct drm_i915_gem_request *request,
gen8_emit_wa_tail(request, cs);
}
-
static const int gen8_emit_breadcrumb_render_sz = 8 + WA_TAIL_DWORDS;
static int gen8_init_rcs_context(struct drm_i915_gem_request *req)
diff --git a/drivers/gpu/drm/i915/intel_ringbuffer.h b/drivers/gpu/drm/i915/intel_ringbuffer.h
index 56d7ae9f298b..891d9555dce6 100644
--- a/drivers/gpu/drm/i915/intel_ringbuffer.h
+++ b/drivers/gpu/drm/i915/intel_ringbuffer.h
@@ -238,6 +238,8 @@ struct intel_engine_execlists {
#define EXECLIST_MAX_PORTS 2
} port[EXECLIST_MAX_PORTS];
+ bool preempt;
+
/**
* @port_mask: number of execlist ports - 1
*/
--
2.14.1
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