On 8/20/2021 15:44, Matthew Brost wrote:
For some users of multi-lrc, e.g. split frame, it isn't safe to preempt
mid BB. To safely enable preemption at the BB boundary, a handshake
between to parent and child is needed. This is implemented via custom
emit_bb_start & emit_fini_breadcrumb functions and enabled via by
via by -> by
default if a context is configured by set parallel extension.
I tend to agree with Tvrtko that this should probably be an opt in
change. Is there a flags word passed in when creating the context?
Also, it's not just a change in pre-emption behaviour but a change in
synchronisation too, right? Previously, if you had a whole bunch of back
to back submissions then one child could run ahead of another and/or the
parent. After this change, there is a forced regroup at the end of each
batch. So while one could end sooner/later than the others, they can't
ever get an entire batch (or more) ahead or behind. Or was that
synchronisation already in there through other means anyway?
Signed-off-by: Matthew Brost <matthew.brost@xxxxxxxxx>
---
drivers/gpu/drm/i915/gt/intel_context.c | 2 +-
drivers/gpu/drm/i915/gt/intel_context_types.h | 3 +
drivers/gpu/drm/i915/gt/uc/intel_guc_fwif.h | 2 +-
.../gpu/drm/i915/gt/uc/intel_guc_submission.c | 283 +++++++++++++++++-
4 files changed, 287 insertions(+), 3 deletions(-)
diff --git a/drivers/gpu/drm/i915/gt/intel_context.c b/drivers/gpu/drm/i915/gt/intel_context.c
index 5615be32879c..2de62649e275 100644
--- a/drivers/gpu/drm/i915/gt/intel_context.c
+++ b/drivers/gpu/drm/i915/gt/intel_context.c
@@ -561,7 +561,7 @@ void intel_context_bind_parent_child(struct intel_context *parent,
GEM_BUG_ON(intel_context_is_child(child));
GEM_BUG_ON(intel_context_is_parent(child));
- parent->guc_number_children++;
+ child->guc_child_index = parent->guc_number_children++;
list_add_tail(&child->guc_child_link,
&parent->guc_child_list);
child->parent = parent;
diff --git a/drivers/gpu/drm/i915/gt/intel_context_types.h b/drivers/gpu/drm/i915/gt/intel_context_types.h
index 713d85b0b364..727f91e7f7c2 100644
--- a/drivers/gpu/drm/i915/gt/intel_context_types.h
+++ b/drivers/gpu/drm/i915/gt/intel_context_types.h
@@ -246,6 +246,9 @@ struct intel_context {
/** @guc_number_children: number of children if parent */
u8 guc_number_children;
+ /** @guc_child_index: index into guc_child_list if child */
+ u8 guc_child_index;
+
/**
* @parent_page: page in context used by parent for work queue,
* work queue descriptor
diff --git a/drivers/gpu/drm/i915/gt/uc/intel_guc_fwif.h b/drivers/gpu/drm/i915/gt/uc/intel_guc_fwif.h
index 6cd26dc060d1..9f61cfa5566a 100644
--- a/drivers/gpu/drm/i915/gt/uc/intel_guc_fwif.h
+++ b/drivers/gpu/drm/i915/gt/uc/intel_guc_fwif.h
@@ -188,7 +188,7 @@ struct guc_process_desc {
u32 wq_status;
u32 engine_presence;
u32 priority;
- u32 reserved[30];
+ u32 reserved[36];
What is this extra space for? All the extra storage is grabbed from
after the end of this structure, isn't it?
} __packed;
#define CONTEXT_REGISTRATION_FLAG_KMD BIT(0)
diff --git a/drivers/gpu/drm/i915/gt/uc/intel_guc_submission.c b/drivers/gpu/drm/i915/gt/uc/intel_guc_submission.c
index 91330525330d..1a18f99bf12a 100644
--- a/drivers/gpu/drm/i915/gt/uc/intel_guc_submission.c
+++ b/drivers/gpu/drm/i915/gt/uc/intel_guc_submission.c
@@ -11,6 +11,7 @@
#include "gt/intel_context.h"
#include "gt/intel_engine_pm.h"
#include "gt/intel_engine_heartbeat.h"
+#include "gt/intel_gpu_commands.h"
#include "gt/intel_gt.h"
#include "gt/intel_gt_irq.h"
#include "gt/intel_gt_pm.h"
@@ -366,10 +367,14 @@ static struct i915_priolist *to_priolist(struct rb_node *rb)
/*
* When using multi-lrc submission an extra page in the context state is
- * reserved for the process descriptor and work queue.
+ * reserved for the process descriptor, work queue, and preempt BB boundary
+ * handshake between the parent + childlren contexts.
*
* The layout of this page is below:
* 0 guc_process_desc
+ * + sizeof(struct guc_process_desc) child go
+ * + CACHELINE_BYTES child join ...
+ * + CACHELINE_BYTES ...
Would be better written as '[num_children]' instead of '...' to make it
clear it is a per child array.
Also, maybe create a struct for this to get rid of the magic '+1's and
'BYTES / sizeof' constructs in the functions below.
* ... unused
* PAGE_SIZE / 2 work queue start
* ... work queue
@@ -1785,6 +1790,30 @@ static int deregister_context(struct intel_context *ce, u32 guc_id, bool loop)
return __guc_action_deregister_context(guc, guc_id, loop);
}
+static inline void clear_children_join_go_memory(struct intel_context *ce)
+{
+ u32 *mem = (u32 *)(__get_process_desc(ce) + 1);
+ u8 i;
+
+ for (i = 0; i < ce->guc_number_children + 1; ++i)
+ mem[i * (CACHELINE_BYTES / sizeof(u32))] = 0;
+}
+
+static inline u32 get_children_go_value(struct intel_context *ce)
+{
+ u32 *mem = (u32 *)(__get_process_desc(ce) + 1);
+
+ return mem[0];
+}
+
+static inline u32 get_children_join_value(struct intel_context *ce,
+ u8 child_index)
+{
+ u32 *mem = (u32 *)(__get_process_desc(ce) + 1);
+
+ return mem[(child_index + 1) * (CACHELINE_BYTES / sizeof(u32))];
+}
+
static void guc_context_policy_init(struct intel_engine_cs *engine,
struct guc_lrc_desc *desc)
{
@@ -1867,6 +1896,8 @@ static int guc_lrc_desc_pin(struct intel_context *ce, bool loop)
desc->context_flags = CONTEXT_REGISTRATION_FLAG_KMD;
guc_context_policy_init(engine, desc);
}
+
+ clear_children_join_go_memory(ce);
}
/*
@@ -2943,6 +2974,31 @@ static const struct intel_context_ops virtual_child_context_ops = {
.get_sibling = guc_virtual_get_sibling,
};
+/*
+ * The below override of the breadcrumbs is enabled when the user configures a
+ * context for parallel submission (multi-lrc, parent-child).
+ *
+ * The overridden breadcrumbs implements an algorithm which allows the GuC to
+ * safely preempt all the hw contexts configured for parallel submission
+ * between each BB. The contract between the i915 and GuC is if the parent
+ * context can be preempted, all the children can be preempted, and the GuC will
+ * always try to preempt the parent before the children. A handshake between the
+ * parent / children breadcrumbs ensures the i915 holds up its end of the deal
+ * creating a window to preempt between each set of BBs.
+ */
+static int emit_bb_start_parent_no_preempt_mid_batch(struct i915_request *rq,
+ u64 offset, u32 len,
+ const unsigned int flags);
+static int emit_bb_start_child_no_preempt_mid_batch(struct i915_request *rq,
+ u64 offset, u32 len,
+ const unsigned int flags);
+static u32 *
+emit_fini_breadcrumb_parent_no_preempt_mid_batch(struct i915_request *rq,
+ u32 *cs);
+static u32 *
+emit_fini_breadcrumb_child_no_preempt_mid_batch(struct i915_request *rq,
+ u32 *cs);
+
static struct intel_context *
guc_create_parallel(struct intel_engine_cs **engines,
unsigned int num_siblings,
@@ -2978,6 +3034,20 @@ guc_create_parallel(struct intel_engine_cs **engines,
}
}
+ parent->engine->emit_bb_start =
+ emit_bb_start_parent_no_preempt_mid_batch;
+ parent->engine->emit_fini_breadcrumb =
+ emit_fini_breadcrumb_parent_no_preempt_mid_batch;
+ parent->engine->emit_fini_breadcrumb_dw =
+ 12 + 4 * parent->guc_number_children;
+ for_each_child(parent, ce) {
+ ce->engine->emit_bb_start =
+ emit_bb_start_child_no_preempt_mid_batch;
+ ce->engine->emit_fini_breadcrumb =
+ emit_fini_breadcrumb_child_no_preempt_mid_batch;
+ ce->engine->emit_fini_breadcrumb_dw = 16;
+ }
+
kfree(siblings);
return parent;
@@ -3362,6 +3432,204 @@ void intel_guc_submission_init_early(struct intel_guc *guc)
guc->submission_selected = __guc_submission_selected(guc);
}
+static inline u32 get_children_go_addr(struct intel_context *ce)
+{
+ GEM_BUG_ON(!intel_context_is_parent(ce));
+
+ return i915_ggtt_offset(ce->state) +
+ __get_process_desc_offset(ce) +
+ sizeof(struct guc_process_desc);
+}
+
+static inline u32 get_children_join_addr(struct intel_context *ce,
+ u8 child_index)
+{
+ GEM_BUG_ON(!intel_context_is_parent(ce));
+
+ return get_children_go_addr(ce) + (child_index + 1) * CACHELINE_BYTES;
+}
+
+#define PARENT_GO_BB 1
+#define PARENT_GO_FINI_BREADCRUMB 0
+#define CHILD_GO_BB 1
+#define CHILD_GO_FINI_BREADCRUMB 0
+static int emit_bb_start_parent_no_preempt_mid_batch(struct i915_request *rq,
+ u64 offset, u32 len,
+ const unsigned int flags)
+{
+ struct intel_context *ce = rq->context;
+ u32 *cs;
+ u8 i;
+
+ GEM_BUG_ON(!intel_context_is_parent(ce));
+
+ cs = intel_ring_begin(rq, 10 + 4 * ce->guc_number_children);
+ if (IS_ERR(cs))
+ return PTR_ERR(cs);
+
+ /* Wait on chidlren */
chidlren -> children
+ for (i = 0; i < ce->guc_number_children; ++i) {
+ *cs++ = (MI_SEMAPHORE_WAIT |
+ MI_SEMAPHORE_GLOBAL_GTT |
+ MI_SEMAPHORE_POLL |
+ MI_SEMAPHORE_SAD_EQ_SDD);
+ *cs++ = PARENT_GO_BB;
+ *cs++ = get_children_join_addr(ce, i);
+ *cs++ = 0;
+ }
+
+ /* Turn off preemption */
+ *cs++ = MI_ARB_ON_OFF | MI_ARB_DISABLE;
+ *cs++ = MI_NOOP;
+
+ /* Tell children go */
+ cs = gen8_emit_ggtt_write(cs,
+ CHILD_GO_BB,
+ get_children_go_addr(ce),
+ 0);
+
+ /* Jump to batch */
+ *cs++ = MI_BATCH_BUFFER_START_GEN8 |
+ (flags & I915_DISPATCH_SECURE ? 0 : BIT(8));
+ *cs++ = lower_32_bits(offset);
+ *cs++ = upper_32_bits(offset);
+ *cs++ = MI_NOOP;
+
+ intel_ring_advance(rq, cs);
+
+ return 0;
+}
+
+static int emit_bb_start_child_no_preempt_mid_batch(struct i915_request *rq,
+ u64 offset, u32 len,
+ const unsigned int flags)
+{
+ struct intel_context *ce = rq->context;
+ u32 *cs;
+
+ GEM_BUG_ON(!intel_context_is_child(ce));
+
+ cs = intel_ring_begin(rq, 12);
+ if (IS_ERR(cs))
+ return PTR_ERR(cs);
+
+ /* Signal parent */
+ cs = gen8_emit_ggtt_write(cs,
+ PARENT_GO_BB,
+ get_children_join_addr(ce->parent,
+ ce->guc_child_index),
+ 0);
+
+ /* Wait parent on for go */
parent on -> on parent
+ *cs++ = (MI_SEMAPHORE_WAIT |
+ MI_SEMAPHORE_GLOBAL_GTT |
+ MI_SEMAPHORE_POLL |
+ MI_SEMAPHORE_SAD_EQ_SDD);
+ *cs++ = CHILD_GO_BB;
+ *cs++ = get_children_go_addr(ce->parent);
+ *cs++ = 0;
+
+ /* Turn off preemption */
+ *cs++ = MI_ARB_ON_OFF | MI_ARB_DISABLE;
+
+ /* Jump to batch */
+ *cs++ = MI_BATCH_BUFFER_START_GEN8 |
+ (flags & I915_DISPATCH_SECURE ? 0 : BIT(8));
+ *cs++ = lower_32_bits(offset);
+ *cs++ = upper_32_bits(offset);
+
+ intel_ring_advance(rq, cs);
+
+ return 0;
+}
+
+static u32 *
+emit_fini_breadcrumb_parent_no_preempt_mid_batch(struct i915_request *rq,
+ u32 *cs)
+{
+ struct intel_context *ce = rq->context;
+ u8 i;
+
+ GEM_BUG_ON(!intel_context_is_parent(ce));
+
+ /* Wait on children */
+ for (i = 0; i < ce->guc_number_children; ++i) {
+ *cs++ = (MI_SEMAPHORE_WAIT |
+ MI_SEMAPHORE_GLOBAL_GTT |
+ MI_SEMAPHORE_POLL |
+ MI_SEMAPHORE_SAD_EQ_SDD);
+ *cs++ = PARENT_GO_FINI_BREADCRUMB;
+ *cs++ = get_children_join_addr(ce, i);
+ *cs++ = 0;
+ }
+
+ /* Turn on preemption */
+ *cs++ = MI_ARB_ON_OFF | MI_ARB_ENABLE;
+ *cs++ = MI_NOOP;
+
+ /* Tell children go */
+ cs = gen8_emit_ggtt_write(cs,
+ CHILD_GO_FINI_BREADCRUMB,
+ get_children_go_addr(ce),
+ 0);
+
+ /* Emit fini breadcrumb */
+ cs = gen8_emit_ggtt_write(cs,
+ rq->fence.seqno,
+ i915_request_active_timeline(rq)->hwsp_offset,
+ 0);
+
+ /* User interrupt */
+ *cs++ = MI_USER_INTERRUPT;
+ *cs++ = MI_NOOP;
+
+ rq->tail = intel_ring_offset(rq, cs);
+
+ return cs;
+}
+
+static u32 *
+emit_fini_breadcrumb_child_no_preempt_mid_batch(struct i915_request *rq, u32 *cs)
+{
+ struct intel_context *ce = rq->context;
+
+ GEM_BUG_ON(!intel_context_is_child(ce));
+
+ /* Turn on preemption */
+ *cs++ = MI_ARB_ON_OFF | MI_ARB_ENABLE;
+ *cs++ = MI_NOOP;
+
+ /* Signal parent */
+ cs = gen8_emit_ggtt_write(cs,
+ PARENT_GO_FINI_BREADCRUMB,
+ get_children_join_addr(ce->parent,
+ ce->guc_child_index),
+ 0);
+
This is backwards compared to the parent?
Parent: wait on children then enable pre-emption
Child: enable pre-emption then signal parent
Makes for a window where the parent is waiting in atomic context for a
signal from a child that has been pre-empted and might not get to run
for some time?
John.
+ /* Wait parent on for go */
+ *cs++ = (MI_SEMAPHORE_WAIT |
+ MI_SEMAPHORE_GLOBAL_GTT |
+ MI_SEMAPHORE_POLL |
+ MI_SEMAPHORE_SAD_EQ_SDD);
+ *cs++ = CHILD_GO_FINI_BREADCRUMB;
+ *cs++ = get_children_go_addr(ce->parent);
+ *cs++ = 0;
+
+ /* Emit fini breadcrumb */
+ cs = gen8_emit_ggtt_write(cs,
+ rq->fence.seqno,
+ i915_request_active_timeline(rq)->hwsp_offset,
+ 0);
+
+ /* User interrupt */
+ *cs++ = MI_USER_INTERRUPT;
+ *cs++ = MI_NOOP;
+
+ rq->tail = intel_ring_offset(rq, cs);
+
+ return cs;
+}
+
static struct intel_context *
g2h_context_lookup(struct intel_guc *guc, u32 desc_idx)
{
@@ -3807,6 +4075,19 @@ void intel_guc_submission_print_context_info(struct intel_guc *guc,
drm_printf(p, "\t\tWQI Status: %u\n\n",
READ_ONCE(desc->wq_status));
+ drm_printf(p, "\t\tNumber Children: %u\n\n",
+ ce->guc_number_children);
+ if (ce->engine->emit_bb_start ==
+ emit_bb_start_parent_no_preempt_mid_batch) {
+ u8 i;
+
+ drm_printf(p, "\t\tChildren Go: %u\n\n",
+ get_children_go_value(ce));
+ for (i = 0; i < ce->guc_number_children; ++i)
+ drm_printf(p, "\t\tChildren Join: %u\n",
+ get_children_join_value(ce, i));
+ }
+
for_each_child(ce, child)
guc_log_context(p, child);
}
