On Sun, Apr 12, 2020 at 12:48:51AM -0700, Sultan Alsawaf wrote:
> On Tue, Apr 07, 2020 at 01:43:45PM -0700, Sultan Alsawaf wrote:
> > From: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx>
> >
> > The major drawback of commit 7e34f4e4aad3 ("drm/i915/gen8+: Add RC6 CTX
> > corruption WA") is that it disables RC6 while Skylake (and friends) is
> > active, and we do not consider the GPU idle until all outstanding
> > requests have been retired and the engine switched over to the kernel
> > context. If userspace is idle, this task falls onto our background idle
> > worker, which only runs roughly once a second, meaning that userspace has
> > to have been idle for a couple of seconds before we enable RC6 again.
> > Naturally, this causes us to consume considerably more energy than
> > before as powersaving is effectively disabled while a display server
> > (here's looking at you Xorg) is running.
> >
> > As execlists will get a completion event as each context is completed,
> > we can use this interrupt to queue a retire worker bound to this engine
> > to cleanup idle timelines. We will then immediately notice the idle
> > engine (without userspace intervention or the aid of the background
> > retire worker) and start parking the GPU. Thus during light workloads,
> > we will do much more work to idle the GPU faster... Hopefully with
> > commensurate power saving!
> >
> > v2: Watch context completions and only look at those local to the engine
> > when retiring to reduce the amount of excess work we perform.
> >
> > Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=112315
> > References: 7e34f4e4aad3 ("drm/i915/gen8+: Add RC6 CTX corruption WA")
> > References: 2248a28384fe ("drm/i915/gen8+: Add RC6 CTX corruption WA")
> > Signed-off-by: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx>
> > Cc: Tvrtko Ursulin <tvrtko.ursulin@xxxxxxxxx>
> > Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@xxxxxxxxx>
> > Link: https://patchwork.freedesktop.org/patch/msgid/20191125105858.1718307-3-chris@xxxxxxxxxxxxxxxxxx
> > (cherry picked from commit 4f88f8747fa43c97c3b3712d8d87295ea757cc51)
> >
> > For the backport to 5.4, struct_mutex needs to be held while retiring so
> > that retirement doesn't race with vma destruction.
> > Signed-off-by: Sultan Alsawaf <sultan@xxxxxxxxxxxxxxx>
> > ---
> > drivers/gpu/drm/i915/gt/intel_engine_cs.c | 2 +
> > drivers/gpu/drm/i915/gt/intel_engine_types.h | 8 ++
> > drivers/gpu/drm/i915/gt/intel_lrc.c | 8 ++
> > drivers/gpu/drm/i915/gt/intel_timeline.c | 1 +
> > .../gpu/drm/i915/gt/intel_timeline_types.h | 3 +
> > drivers/gpu/drm/i915/i915_request.c | 75 +++++++++++++++++++
> > drivers/gpu/drm/i915/i915_request.h | 4 +
> > 7 files changed, 101 insertions(+)
> >
> > diff --git a/drivers/gpu/drm/i915/gt/intel_engine_cs.c b/drivers/gpu/drm/i915/gt/intel_engine_cs.c
> > index 4ce8626b140e..f732a2177cd0 100644
> > --- a/drivers/gpu/drm/i915/gt/intel_engine_cs.c
> > +++ b/drivers/gpu/drm/i915/gt/intel_engine_cs.c
> > @@ -600,6 +600,7 @@ static int intel_engine_setup_common(struct intel_engine_cs *engine)
> > intel_engine_init_hangcheck(engine);
> > intel_engine_init_cmd_parser(engine);
> > intel_engine_init__pm(engine);
> > + intel_engine_init_retire(engine);
> >
> > intel_engine_pool_init(&engine->pool);
> >
> > @@ -807,6 +808,7 @@ void intel_engine_cleanup_common(struct intel_engine_cs *engine)
> >
> > cleanup_status_page(engine);
> >
> > + intel_engine_fini_retire(engine);
> > intel_engine_pool_fini(&engine->pool);
> > intel_engine_fini_breadcrumbs(engine);
> > intel_engine_cleanup_cmd_parser(engine);
> > diff --git a/drivers/gpu/drm/i915/gt/intel_engine_types.h b/drivers/gpu/drm/i915/gt/intel_engine_types.h
> > index c77c9518c58b..1eb7189f88e1 100644
> > --- a/drivers/gpu/drm/i915/gt/intel_engine_types.h
> > +++ b/drivers/gpu/drm/i915/gt/intel_engine_types.h
> > @@ -471,6 +471,14 @@ struct intel_engine_cs {
> >
> > struct intel_engine_execlists execlists;
> >
> > + /*
> > + * Keep track of completed timelines on this engine for early
> > + * retirement with the goal of quickly enabling powersaving as
> > + * soon as the engine is idle.
> > + */
> > + struct intel_timeline *retire;
> > + struct work_struct retire_work;
> > +
> > /* status_notifier: list of callbacks for context-switch changes */
> > struct atomic_notifier_head context_status_notifier;
> >
> > diff --git a/drivers/gpu/drm/i915/gt/intel_lrc.c b/drivers/gpu/drm/i915/gt/intel_lrc.c
> > index 66f6d1a897f2..a1538c8f7922 100644
> > --- a/drivers/gpu/drm/i915/gt/intel_lrc.c
> > +++ b/drivers/gpu/drm/i915/gt/intel_lrc.c
> > @@ -606,6 +606,14 @@ __execlists_schedule_out(struct i915_request *rq,
> > {
> > struct intel_context * const ce = rq->hw_context;
> >
> > + /*
> > + * If we have just completed this context, the engine may now be
> > + * idle and we want to re-enter powersaving.
> > + */
> > + if (list_is_last(&rq->link, &ce->timeline->requests) &&
> > + i915_request_completed(rq))
> > + intel_engine_add_retire(engine, ce->timeline);
> > +
> > intel_engine_context_out(engine);
> > execlists_context_status_change(rq, INTEL_CONTEXT_SCHEDULE_OUT);
> > intel_gt_pm_put(engine->gt);
> > diff --git a/drivers/gpu/drm/i915/gt/intel_timeline.c b/drivers/gpu/drm/i915/gt/intel_timeline.c
> > index 9cb01d9828f1..63515e3caaf2 100644
> > --- a/drivers/gpu/drm/i915/gt/intel_timeline.c
> > +++ b/drivers/gpu/drm/i915/gt/intel_timeline.c
> > @@ -282,6 +282,7 @@ void intel_timeline_fini(struct intel_timeline *timeline)
> > {
> > GEM_BUG_ON(atomic_read(&timeline->pin_count));
> > GEM_BUG_ON(!list_empty(&timeline->requests));
> > + GEM_BUG_ON(timeline->retire);
> >
> > if (timeline->hwsp_cacheline)
> > cacheline_free(timeline->hwsp_cacheline);
> > diff --git a/drivers/gpu/drm/i915/gt/intel_timeline_types.h b/drivers/gpu/drm/i915/gt/intel_timeline_types.h
> > index 2b1baf2fcc8e..adf2d14ef647 100644
> > --- a/drivers/gpu/drm/i915/gt/intel_timeline_types.h
> > +++ b/drivers/gpu/drm/i915/gt/intel_timeline_types.h
> > @@ -65,6 +65,9 @@ struct intel_timeline {
> > */
> > struct i915_active_request last_request;
> >
> > + /** A chain of completed timelines ready for early retirement. */
> > + struct intel_timeline *retire;
> > +
> > /**
> > * We track the most recent seqno that we wait on in every context so
> > * that we only have to emit a new await and dependency on a more
> > diff --git a/drivers/gpu/drm/i915/i915_request.c b/drivers/gpu/drm/i915/i915_request.c
> > index 0d39038898d4..35457fda350c 100644
> > --- a/drivers/gpu/drm/i915/i915_request.c
> > +++ b/drivers/gpu/drm/i915/i915_request.c
> > @@ -600,6 +600,81 @@ static void retire_requests(struct intel_timeline *tl)
> > break;
> > }
> >
> > +static void engine_retire(struct work_struct *work)
> > +{
> > + struct intel_engine_cs *engine =
> > + container_of(work, typeof(*engine), retire_work);
> > + struct intel_timeline *tl = xchg(&engine->retire, NULL);
> > +
> > + do {
> > + struct intel_timeline *next = xchg(&tl->retire, NULL);
> > +
> > + /*
> > + * Our goal here is to retire _idle_ timelines as soon as
> > + * possible (as they are idle, we do not expect userspace
> > + * to be cleaning up anytime soon).
> > + *
> > + * If the timeline is currently locked, either it is being
> > + * retired elsewhere or about to be!
> > + */
> > + mutex_lock(&engine->i915->drm.struct_mutex);
> > + if (mutex_trylock(&tl->mutex)) {
> > + retire_requests(tl);
> > + mutex_unlock(&tl->mutex);
> > + }
> > + mutex_unlock(&engine->i915->drm.struct_mutex);
> > + intel_timeline_put(tl);
> > +
> > + GEM_BUG_ON(!next);
> > + tl = ptr_mask_bits(next, 1);
> > + } while (tl);
> > +}
> > +
> > +static bool add_retire(struct intel_engine_cs *engine,
> > + struct intel_timeline *tl)
> > +{
> > + struct intel_timeline *first;
> > +
> > + /*
> > + * We open-code a llist here to include the additional tag [BIT(0)]
> > + * so that we know when the timeline is already on a
> > + * retirement queue: either this engine or another.
> > + *
> > + * However, we rely on that a timeline can only be active on a single
> > + * engine at any one time and that add_retire() is called before the
> > + * engine releases the timeline and transferred to another to retire.
> > + */
> > +
> > + if (READ_ONCE(tl->retire)) /* already queued */
> > + return false;
> > +
> > + intel_timeline_get(tl);
> > + first = READ_ONCE(engine->retire);
> > + do
> > + tl->retire = ptr_pack_bits(first, 1, 1);
> > + while (!try_cmpxchg(&engine->retire, &first, tl));
> > +
> > + return !first;
> > +}
> > +
> > +void intel_engine_add_retire(struct intel_engine_cs *engine,
> > + struct intel_timeline *tl)
> > +{
> > + if (add_retire(engine, tl))
> > + schedule_work(&engine->retire_work);
> > +}
> > +
> > +void intel_engine_init_retire(struct intel_engine_cs *engine)
> > +{
> > + INIT_WORK(&engine->retire_work, engine_retire);
> > +}
> > +
> > +void intel_engine_fini_retire(struct intel_engine_cs *engine)
> > +{
> > + flush_work(&engine->retire_work);
> > + GEM_BUG_ON(engine->retire);
> > +}
> > +
> > static noinline struct i915_request *
> > request_alloc_slow(struct intel_timeline *tl, gfp_t gfp)
> > {
> > diff --git a/drivers/gpu/drm/i915/i915_request.h b/drivers/gpu/drm/i915/i915_request.h
> > index 3a3e7bbf19ff..40caa2f3f4a4 100644
> > --- a/drivers/gpu/drm/i915/i915_request.h
> > +++ b/drivers/gpu/drm/i915/i915_request.h
> > @@ -445,5 +445,9 @@ static inline bool i915_request_has_nopreempt(const struct i915_request *rq)
> > }
> >
> > bool i915_retire_requests(struct drm_i915_private *i915);
> > +void intel_engine_init_retire(struct intel_engine_cs *engine);
> > +void intel_engine_add_retire(struct intel_engine_cs *engine,
> > + struct intel_timeline *tl);
> > +void intel_engine_fini_retire(struct intel_engine_cs *engine);
> >
> > #endif /* I915_REQUEST_H */
> > --
> > 2.26.0
> >
>
> Hi Greg,
>
> Could you queue this one up as well?
What is the git commit id of this in Linus's tree?
