On 27/03/18 16:27, Chris Wilson wrote:
Quoting Tomasz Lis (2018-03-27 16:17:59)
The patch adds support of preempt-to-idle requesting by setting a proper
bit within Execlist Control Register, and receiving preemption result from
Context Status Buffer.
Preemption in previous gens required a special batch buffer to be executed,
so the Command Streamer never preempted to idle directly. In Icelake it is
possible, as there is a hardware mechanism to inform the kernel about
status of the preemption request.
This patch does not cover using the new preemption mechanism when GuC is
active.
Bspec: 18922
Signed-off-by: Tomasz Lis <tomasz.lis@xxxxxxxxx>
---
drivers/gpu/drm/i915/i915_drv.h | 2 ++
drivers/gpu/drm/i915/i915_pci.c | 3 ++-
drivers/gpu/drm/i915/intel_device_info.h | 1 +
drivers/gpu/drm/i915/intel_lrc.c | 45 +++++++++++++++++++++++++++-----
drivers/gpu/drm/i915/intel_lrc.h | 1 +
5 files changed, 45 insertions(+), 7 deletions(-)
diff --git a/drivers/gpu/drm/i915/i915_drv.h b/drivers/gpu/drm/i915/i915_drv.h
index 800230b..c32580b 100644
--- a/drivers/gpu/drm/i915/i915_drv.h
+++ b/drivers/gpu/drm/i915/i915_drv.h
@@ -2514,6 +2514,8 @@ intel_info(const struct drm_i915_private *dev_priv)
((dev_priv)->info.has_logical_ring_elsq)
#define HAS_LOGICAL_RING_PREEMPTION(dev_priv) \
((dev_priv)->info.has_logical_ring_preemption)
+#define HAS_HW_PREEMPT_TO_IDLE(dev_priv) \
+ ((dev_priv)->info.has_hw_preempt_to_idle)
#define HAS_EXECLISTS(dev_priv) HAS_LOGICAL_RING_CONTEXTS(dev_priv)
diff --git a/drivers/gpu/drm/i915/i915_pci.c b/drivers/gpu/drm/i915/i915_pci.c
index 4364922..66b6700 100644
--- a/drivers/gpu/drm/i915/i915_pci.c
+++ b/drivers/gpu/drm/i915/i915_pci.c
@@ -595,7 +595,8 @@ static const struct intel_device_info intel_cannonlake_info = {
GEN(11), \
.ddb_size = 2048, \
.has_csr = 0, \
- .has_logical_ring_elsq = 1
+ .has_logical_ring_elsq = 1, \
+ .has_hw_preempt_to_idle = 1
static const struct intel_device_info intel_icelake_11_info = {
GEN11_FEATURES,
diff --git a/drivers/gpu/drm/i915/intel_device_info.h b/drivers/gpu/drm/i915/intel_device_info.h
index 933e316..4eb97b5 100644
--- a/drivers/gpu/drm/i915/intel_device_info.h
+++ b/drivers/gpu/drm/i915/intel_device_info.h
@@ -98,6 +98,7 @@ enum intel_platform {
func(has_logical_ring_contexts); \
func(has_logical_ring_elsq); \
func(has_logical_ring_preemption); \
+ func(has_hw_preempt_to_idle); \
func(has_overlay); \
func(has_pooled_eu); \
func(has_psr); \
diff --git a/drivers/gpu/drm/i915/intel_lrc.c b/drivers/gpu/drm/i915/intel_lrc.c
index ba7f783..1a22de4 100644
--- a/drivers/gpu/drm/i915/intel_lrc.c
+++ b/drivers/gpu/drm/i915/intel_lrc.c
@@ -153,6 +153,7 @@
#define GEN8_CTX_STATUS_ACTIVE_IDLE (1 << 3)
#define GEN8_CTX_STATUS_COMPLETE (1 << 4)
#define GEN8_CTX_STATUS_LITE_RESTORE (1 << 15)
+#define GEN11_CTX_STATUS_PREEMPT_IDLE (1 << 29)
#define GEN8_CTX_STATUS_COMPLETED_MASK \
(GEN8_CTX_STATUS_COMPLETE | GEN8_CTX_STATUS_PREEMPTED)
@@ -183,7 +184,9 @@ static inline bool need_preempt(const struct intel_engine_cs *engine,
const struct i915_request *last,
int prio)
{
- return engine->i915->preempt_context && prio > max(rq_prio(last), 0);
+ return (engine->i915->preempt_context ||
+ HAS_HW_PREEMPT_TO_IDLE(engine->i915)) &&
Well, you haven't actually disabled allocating the preempt_context so...
But at any rate, making this an engine->flag would eliminate one pointer
dance.
Can't we re-use I915_SCHEDULER_CAP_PREEMPTION in
engine->i915->caps.scheduler? That btw like here to be set if
i915->preempt_context || HAS_HW_PREEMPT_TO_IDLE(i915)
+ prio > max(rq_prio(last), 0);
}
/**
@@ -535,6 +538,25 @@ static void inject_preempt_context(struct intel_engine_cs *engine)
execlists_set_active(&engine->execlists, EXECLISTS_ACTIVE_PREEMPT);
}
+static void gen11_preempt_to_idle(struct intel_engine_cs *engine)
+{
+ struct intel_engine_execlists *execlists = &engine->execlists;
+
+ GEM_TRACE("%s\n", engine->name);
+
+ /*
+ * hardware which HAS_HW_PREEMPT_TO_IDLE(), always also
+ * HAS_LOGICAL_RING_ELSQ(), so we can assume ctrl_reg is set
+ */
+ GEM_BUG_ON(execlists->ctrl_reg != NULL);
Shouldn't this check be the other way around?
+
+ /* trigger preemption to idle */
+ writel(EL_CTRL_PREEMPT_TO_IDLE, execlists->ctrl_reg);
Future plans? Because just inserting the branch into the setter of
inject_preempt_context() resolves a lot of conflicts with other work.
@@ -962,10 +987,13 @@ static void execlists_submission_tasklet(unsigned long data)
status, buf[2*head + 1],
execlists->active);
- if (status & (GEN8_CTX_STATUS_IDLE_ACTIVE |
- GEN8_CTX_STATUS_PREEMPTED))
+ /* Check if switched to active or preempted to active */
+ if ((status & (GEN8_CTX_STATUS_IDLE_ACTIVE |
+ GEN8_CTX_STATUS_PREEMPTED)) &&
+ !(status & GEN11_CTX_STATUS_PREEMPT_IDLE))
Setting HWACK here is harmless as it gets cleared again. Unless, there
is some oddity in the code flow.
There is actually some oddity, but it is more on the HW side. A preempt
to idle can potentially land on an already idle HW, in which case
GEN8_CTX_STATUS_ACTIVE_IDLE is not set and GEN8_CTX_STATUS_IDLE_ACTIVE
is set instead. In this case without this check on
GEN11_CTX_STATUS_PREEMPT_IDLE we would set the HWACK here but we
wouldn't call the clear below. Not sure if we end up clearing the flag
elsewhere, but that doesn't look too nice IMHO.
BTW, the relevant CSB bits coming out in the 2 preempt to idle cases are
as follows:
preempt active HW:
GEN11_CTX_STATUS_PREEMPT_IDLE | GEN8_CTX_STATUS_ACTIVE_IDLE |
GEN8_CTX_STATUS_PREEMPTED
Preempt idle HW:
GEN11_CTX_STATUS_PREEMPT_IDLE | GEN8_CTX_STATUS_IDLE_ACTIVE
Daniele
execlists_set_active(execlists,
EXECLISTS_ACTIVE_HWACK);
+
if (status & GEN8_CTX_STATUS_ACTIVE_IDLE)
execlists_clear_active(execlists,
EXECLISTS_ACTIVE_HWACK);
@@ -976,8 +1004,13 @@ static void execlists_submission_tasklet(unsigned long data)
/* We should never get a COMPLETED | IDLE_ACTIVE! */
GEM_BUG_ON(status & GEN8_CTX_STATUS_IDLE_ACTIVE);
- if (status & GEN8_CTX_STATUS_COMPLETE &&
- buf[2*head + 1] == execlists->preempt_complete_status) {
+ /*
+ * Check if preempted to real idle, either directly or
+ * the preemptive context already finished executing
+ */
+ if ((status & GEN11_CTX_STATUS_PREEMPT_IDLE) ||
+ (status & GEN8_CTX_STATUS_COMPLETE &&
+ buf[2*head + 1] == execlists->preempt_complete_status)) {
GEM_TRACE("%s preempt-idle\n", engine->name);
Hmm. I was hoping that we would be able to engineer a single check to
cover all sins. Might have been overly optimistic, but I can dream.
-Chris
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