Re: [Intel-gfx] [PATCH 23/27] drm/i915/guc: Implement no mid batch preemption for multi-lrc

Matthew Brost
2021-09-10T20:54:39Z

On Fri, Sep 10, 2021 at 12:25:43PM +0100, Tvrtko Ursulin wrote:
>
> On 20/08/2021 23:44, 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
> > default if a context is configured by set parallel extension.
>
> FWIW I think it's wrong to hardcode the requirements of a particular
> hardware generation fixed media pipeline into the uapi. IMO better solution
> was when concept of parallel submission was decoupled from the no preemption
> mid batch preambles. Otherwise might as well call the extension
> I915_CONTEXT_ENGINES_EXT_MEDIA_SPLIT_FRAME_SUBMIT or something.
>

I don't disagree but this where we landed per Daniel Vetter's feedback -
default to what our current hardware supports and extend it later to
newer hardware / requirements as needed.

Matt

> Regards,
>
> Tvrtko
> > Signed-off-by: Matthew Brost <matthew.brost@intel.com>
> > ---
> > 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];
> > } __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 ...
> > * ... 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 */
> > + 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 */
> > + *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);
> > +
> > + /* 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);
> > }
> >