Quoting Tvrtko Ursulin (2018-09-28 14:04:34)
>
> On 27/09/2018 14:05, Chris Wilson wrote:
> > Quoting Tvrtko Ursulin (2018-09-25 10:48:44)
> >>
> >> On 25/09/2018 09:32, Chris Wilson wrote:
> >>> As we are about to allow ourselves to slightly bump the user priority
> >>> into a few different sublevels, packthose internal priority lists
> >>> into the same i915_priolist to keep the rbtree compact and avoid having
> >>> to allocate the default user priority even after the internal bumping.
> >>> The downside to having an requests[] rather than a node per active list,
> >>> is that we then have to walk over the empty higher priority lists. To
> >>> compensate, we track the active buckets and use a small bitmap to skip
> >>> over any inactive ones.
> >>>
> >>> v2: Use MASK of internal levels to simplify our usage.
> >>>
> >>> Signed-off-by: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx>
> >>> Cc: Tvrtko Ursulin <tvrtko.ursulin@xxxxxxxxx>
> >>> ---
> >>> drivers/gpu/drm/i915/intel_engine_cs.c | 6 +-
> >>> drivers/gpu/drm/i915/intel_guc_submission.c | 12 ++-
> >>> drivers/gpu/drm/i915/intel_lrc.c | 87 ++++++++++++++-------
> >>> drivers/gpu/drm/i915/intel_ringbuffer.h | 13 ++-
> >>> 4 files changed, 80 insertions(+), 38 deletions(-)
> >>>
> >>> diff --git a/drivers/gpu/drm/i915/intel_engine_cs.c b/drivers/gpu/drm/i915/intel_engine_cs.c
> >>> index 217ed3ee1cab..83f2f7774c1f 100644
> >>> --- a/drivers/gpu/drm/i915/intel_engine_cs.c
> >>> +++ b/drivers/gpu/drm/i915/intel_engine_cs.c
> >>> @@ -1534,10 +1534,10 @@ void intel_engine_dump(struct intel_engine_cs *engine,
> >>> count = 0;
> >>> drm_printf(m, "\t\tQueue priority: %d\n", execlists->queue_priority);
> >>> for (rb = rb_first_cached(&execlists->queue); rb; rb = rb_next(rb)) {
> >>> - struct i915_priolist *p =
> >>> - rb_entry(rb, typeof(*p), node);
> >>> + struct i915_priolist *p = rb_entry(rb, typeof(*p), node);
> >>> + int i;
> >>>
> >>> - list_for_each_entry(rq, &p->requests, sched.link) {
> >>> + priolist_for_each_request(rq, p, i) {
> >>> if (count++ < MAX_REQUESTS_TO_SHOW - 1)
> >>> print_request(m, rq, "\t\tQ ");
> >>> else
> >>> diff --git a/drivers/gpu/drm/i915/intel_guc_submission.c b/drivers/gpu/drm/i915/intel_guc_submission.c
> >>> index 4874a212754c..ac862b42f6a1 100644
> >>> --- a/drivers/gpu/drm/i915/intel_guc_submission.c
> >>> +++ b/drivers/gpu/drm/i915/intel_guc_submission.c
> >>> @@ -746,30 +746,28 @@ static bool __guc_dequeue(struct intel_engine_cs *engine)
> >>> while ((rb = rb_first_cached(&execlists->queue))) {
> >>> struct i915_priolist *p = to_priolist(rb);
> >>> struct i915_request *rq, *rn;
> >>> + int i;
> >>>
> >>> - list_for_each_entry_safe(rq, rn, &p->requests, sched.link) {
> >>> + priolist_for_each_request_consume(rq, rn, p, i) {
> >>> if (last && rq->hw_context != last->hw_context) {
> >>> - if (port == last_port) {
> >>> - __list_del_many(&p->requests,
> >>> - &rq->sched.link);
> >>> + if (port == last_port)
> >>> goto done;
> >>> - }
> >>>
> >>> if (submit)
> >>> port_assign(port, last);
> >>> port++;
> >>> }
> >>>
> >>> - INIT_LIST_HEAD(&rq->sched.link);
> >>> + list_del_init(&rq->sched.link);
> >>>
> >>> __i915_request_submit(rq);
> >>> trace_i915_request_in(rq, port_index(port, execlists));
> >>> +
> >>> last = rq;
> >>> submit = true;
> >>> }
> >>>
> >>> rb_erase_cached(&p->node, &execlists->queue);
> >>> - INIT_LIST_HEAD(&p->requests);
> >>> if (p->priority != I915_PRIORITY_NORMAL)
> >>> kmem_cache_free(engine->i915->priorities, p);
> >>> }
> >>> diff --git a/drivers/gpu/drm/i915/intel_lrc.c b/drivers/gpu/drm/i915/intel_lrc.c
> >>> index e8de250c3413..b1b3f67d1120 100644
> >>> --- a/drivers/gpu/drm/i915/intel_lrc.c
> >>> +++ b/drivers/gpu/drm/i915/intel_lrc.c
> >>> @@ -259,14 +259,49 @@ intel_lr_context_descriptor_update(struct i915_gem_context *ctx,
> >>> ce->lrc_desc = desc;
> >>> }
> >>>
> >>> -static struct i915_priolist *
> >>> +static void assert_priolists(struct intel_engine_execlists * const execlists,
> >>> + int queue_priority)
> >>> +{
> >>> + struct rb_node *rb;
> >>> + int last_prio, i;
> >>> +
> >>> + if (!IS_ENABLED(CONFIG_DRM_I915_DEBUG_GEM))
> >>> + return;
> >>> +
> >>> + GEM_BUG_ON(rb_first_cached(&execlists->queue) !=
> >>> + rb_first(&execlists->queue.rb_root));
> >>> +
> >>> + last_prio = (queue_priority >> I915_USER_PRIORITY_SHIFT) + 1;
> >>> + for (rb = rb_first_cached(&execlists->queue); rb; rb = rb_next(rb)) {
> >>> + struct i915_priolist *p = to_priolist(rb);
> >>> +
> >>> + GEM_BUG_ON(p->priority >= last_prio);
> >>> + last_prio = p->priority;
> >>> +
> >>> + GEM_BUG_ON(!p->used);
> >>> + for (i = 0; i < ARRAY_SIZE(p->requests); i++) {
> >>> + if (list_empty(&p->requests[i]))
> >>> + continue;
> >>> +
> >>> + GEM_BUG_ON(!(p->used & BIT(i)));
> >>> + }
> >>> + }
> >>> +}
> >>> +
> >>> +static struct list_head *
> >>> lookup_priolist(struct intel_engine_cs *engine, int prio)
> >>> {
> >>> struct intel_engine_execlists * const execlists = &engine->execlists;
> >>> struct i915_priolist *p;
> >>> struct rb_node **parent, *rb;
> >>> bool first = true;
> >>> + int idx, i;
> >>> +
> >>> + assert_priolists(execlists, INT_MAX);
> >>>
> >>> + /* buckets sorted from highest [in slot 0] to lowest priority */
> >>> + idx = I915_PRIORITY_MASK - (prio & I915_PRIORITY_MASK);
> >>
> >> How about:
> >>
> >> #define I915_INTERNAL_PRIO(p) (p & I915_PRIORITY_MASK)
> >
> > Not convinced. It's the only place we use it (one use of MASK later to
> > assert correct less). There's two views, here the user/kernel priority
> > levels are not as important as what we are concerned about are the split
> > lists with the chunking of lowest priority bits. At the extreme we could
> > separate the two and make the chunks BITS_PER_LONG -- I think that's a
> > waste and my goal was simply to avoid kmallocs for the common case of
> > default user priority.
> >
> > The intention is that we don't even think about the user/internal split,
> > and simply consider it an integrated field, with most positive
> > priorities executing first and most negative last.
>
> I just find MASK - INT confusing, those two data flavours do not match
> in my head. With the local macro I clarified that we are getting an INT
> from prio, and then the bit you did not quote I suggested we do not
> substract from the mask but from the count - 1. It is effectively the
> same thing just IMHO easier to understand while reading the code. You
> can skip the macro and decrement from the count, I'd be happy with that
> as well.
I swear that COUNT-1 was the bit you complained about last time ;)
I put the comment there to explain why we reverse the index, as leftmost
is highest priority.
Preemptive r-b for COUNT-1 - (prio & I915_PRIORITY_MASK) then?
-Chris
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