On Thu, Aug 12, 2021 at 5:10 PM Jason Ekstrand <jason@xxxxxxxxxxxxxx> wrote:
> On Tue, Aug 10, 2021 at 8:05 AM Daniel Vetter <daniel.vetter@xxxxxxxx> wrote:
> >
> > This essentially reverts
> >
> > commit 89ff76bf9b3b0b86e6bbe344bd6378d8661303fc
> > Author: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx>
> > Date: Thu Apr 2 13:42:18 2020 +0100
> >
> > drm/i915/gem: Utilize rcu iteration of context engines
> >
> > Note that the other use of __context_engines_await have disappeard in
> > the following commits:
> >
> > ccbc1b97948a ("drm/i915/gem: Don't allow changing the VM on running contexts (v4)")
> > c7a71fc8ee04 ("drm/i915: Drop getparam support for I915_CONTEXT_PARAM_ENGINES")
> > 4a766ae40ec8 ("drm/i915: Drop the CONTEXT_CLONE API (v2)")
> >
> > None of these have any business to optimize their engine lookup with
> > rcu, unless extremely convincing benchmark data and a solid analysis
> > why we can't make that workload (whatever it is that does) faster with
> > a proper design fix.
> >
> > Also since there's only one caller of context_apply_all left and it's
> > really just a loop, inline it and then inline the lopp body too. This
> > is how all other callers that take the engine lock loop over engines,
> > it's much simpler.
> >
> > Signed-off-by: Daniel Vetter <daniel.vetter@xxxxxxxxx>
> > Cc: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx>
> > Cc: Mika Kuoppala <mika.kuoppala@xxxxxxxxxxxxxxx>
> > Cc: Daniel Vetter <daniel.vetter@xxxxxxxx>
> > Cc: Jason Ekstrand <jason@xxxxxxxxxxxxxx>
> > Cc: Tvrtko Ursulin <tvrtko.ursulin@xxxxxxxxx>
> > Cc: Joonas Lahtinen <joonas.lahtinen@xxxxxxxxxxxxxxx>
> > Cc: Matthew Brost <matthew.brost@xxxxxxxxx>
> > ---
> > drivers/gpu/drm/i915/gem/i915_gem_context.c | 72 ++++-----------------
> > 1 file changed, 14 insertions(+), 58 deletions(-)
> >
> > diff --git a/drivers/gpu/drm/i915/gem/i915_gem_context.c b/drivers/gpu/drm/i915/gem/i915_gem_context.c
> > index dbaeb924a437..fd169cf2f75a 100644
> > --- a/drivers/gpu/drm/i915/gem/i915_gem_context.c
> > +++ b/drivers/gpu/drm/i915/gem/i915_gem_context.c
> > @@ -1284,49 +1284,6 @@ static int __context_set_persistence(struct i915_gem_context *ctx, bool state)
> > return 0;
> > }
> >
> > -static inline struct i915_gem_engines *
> > -__context_engines_await(const struct i915_gem_context *ctx,
> > - bool *user_engines)
> > -{
> > - struct i915_gem_engines *engines;
> > -
> > - rcu_read_lock();
> > - do {
> > - engines = rcu_dereference(ctx->engines);
> > - GEM_BUG_ON(!engines);
> > -
> > - if (user_engines)
> > - *user_engines = i915_gem_context_user_engines(ctx);
> > -
> > - /* successful await => strong mb */
> > - if (unlikely(!i915_sw_fence_await(&engines->fence)))
>
> Ugh... The first time I looked at this I thought the SW fence meant it
> was actually waiting on something. But, no, it's just making sure the
> engines object still exists. *sigh* Burn it!
... why did you force me to page this in again, I already forgot.
> Reviewed-by: Jason Ekstrand <jason@xxxxxxxxxxxxxx>
Merged to drm-intel-gt-next, thanks for the review.
-Daniel
>
> > - continue;
> > -
> > - if (likely(engines == rcu_access_pointer(ctx->engines)))
> > - break;
> > -
> > - i915_sw_fence_complete(&engines->fence);
> > - } while (1);
> > - rcu_read_unlock();
> > -
> > - return engines;
> > -}
> > -
> > -static void
> > -context_apply_all(struct i915_gem_context *ctx,
> > - void (*fn)(struct intel_context *ce, void *data),
> > - void *data)
> > -{
> > - struct i915_gem_engines_iter it;
> > - struct i915_gem_engines *e;
> > - struct intel_context *ce;
> > -
> > - e = __context_engines_await(ctx, NULL);
> > - for_each_gem_engine(ce, e, it)
> > - fn(ce, data);
> > - i915_sw_fence_complete(&e->fence);
> > -}
> > -
> > static struct i915_gem_context *
> > i915_gem_create_context(struct drm_i915_private *i915,
> > const struct i915_gem_proto_context *pc)
> > @@ -1776,23 +1733,11 @@ set_persistence(struct i915_gem_context *ctx,
> > return __context_set_persistence(ctx, args->value);
> > }
> >
> > -static void __apply_priority(struct intel_context *ce, void *arg)
> > -{
> > - struct i915_gem_context *ctx = arg;
> > -
> > - if (!intel_engine_has_timeslices(ce->engine))
> > - return;
> > -
> > - if (ctx->sched.priority >= I915_PRIORITY_NORMAL &&
> > - intel_engine_has_semaphores(ce->engine))
> > - intel_context_set_use_semaphores(ce);
> > - else
> > - intel_context_clear_use_semaphores(ce);
> > -}
> > -
> > static int set_priority(struct i915_gem_context *ctx,
> > const struct drm_i915_gem_context_param *args)
> > {
> > + struct i915_gem_engines_iter it;
> > + struct intel_context *ce;
> > int err;
> >
> > err = validate_priority(ctx->i915, args);
> > @@ -1800,7 +1745,18 @@ static int set_priority(struct i915_gem_context *ctx,
> > return err;
> >
> > ctx->sched.priority = args->value;
> > - context_apply_all(ctx, __apply_priority, ctx);
> > +
> > + for_each_gem_engine(ce, i915_gem_context_lock_engines(ctx), it) {
> > + if (!intel_engine_has_timeslices(ce->engine))
> > + continue;
> > +
> > + if (ctx->sched.priority >= I915_PRIORITY_NORMAL &&
> > + intel_engine_has_semaphores(ce->engine))
> > + intel_context_set_use_semaphores(ce);
> > + else
> > + intel_context_clear_use_semaphores(ce);
> > + }
> > + i915_gem_context_unlock_engines(ctx);
> >
> > return 0;
> > }
> > --
> > 2.32.0
> >
--
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch
