Commit b9709057 authored by Daniel Vetter's avatar Daniel Vetter
Browse files

drm/i915: Use locked access to ctx->engines in set_priority 



This essentially reverts

commit 89ff76bf
Author: Chris Wilson <chris@chris-wilson.co.uk>
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:

ccbc1b97 ("drm/i915/gem: Don't allow changing the VM on running contexts (v4)")
c7a71fc8 ("drm/i915: Drop getparam support for I915_CONTEXT_PARAM_ENGINES")
4a766ae4 ("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.

Reviewed-by: default avatarJason Ekstrand <jason@jlekstrand.net>
Signed-off-by: default avatarDaniel Vetter <daniel.vetter@intel.com>
Cc: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Mika Kuoppala <mika.kuoppala@linux.intel.com>
Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
Cc: Jason Ekstrand <jason@jlekstrand.net>
Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Cc: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Cc: Matthew Brost <matthew.brost@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20210810130523.1972031-1-daniel.vetter@ffwll.ch
parent d16de9a2

drivers/gpu/drm/i915/gem/i915_gem_context.c

+14 −58
Original line number Diff line number Diff line
@@ -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)))

			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;

}