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

This essentially reverts

commit 89ff76bf9b3b0b86e6bbe344bd6378d8661303fc
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:

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.

Reviewed-by: Jason Ekstrand <jason@jlekstrand.net>
Signed-off-by: Daniel 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

diff --git a/drivers/gpu/drm/i915/gem/i915_gem_context.c b/drivers/gpu/drm/i915/gem/i915_gem_context.c
index dbaeb92..fd169cf 100644 (file)
--- 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)))
-                       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;
 }