drm/i915/gem: Reduce ctx->engines_mutex for get_engines()

Take a snapshot of the ctx->engines, so we can avoid taking the
ctx->engines_mutex for a mere read in get_engines().

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: Andi Shyti <andi.shyti@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20210114135612.13210-4-chris@chris-wilson.co.uk

diff --git a/drivers/gpu/drm/i915/gem/i915_gem_context.c b/drivers/gpu/drm/i915/gem/i915_gem_context.c
index 4a709c6..4d2f40c 100644 (file)
--- a/drivers/gpu/drm/i915/gem/i915_gem_context.c
+++ b/drivers/gpu/drm/i915/gem/i915_gem_context.c
@@ -1843,27 +1843,6 @@ replace:
        return 0;
 }
 
-static struct i915_gem_engines *
-__copy_engines(struct i915_gem_engines *e)
-{
-       struct i915_gem_engines *copy;
-       unsigned int n;
-
-       copy = alloc_engines(e->num_engines);
-       if (!copy)
-               return ERR_PTR(-ENOMEM);
-
-       for (n = 0; n < e->num_engines; n++) {
-               if (e->engines[n])
-                       copy->engines[n] = intel_context_get(e->engines[n]);
-               else
-                       copy->engines[n] = NULL;
-       }
-       copy->num_engines = n;
-
-       return copy;
-}
-
 static int
 get_engines(struct i915_gem_context *ctx,
            struct drm_i915_gem_context_param *args)
@@ -1871,19 +1850,17 @@ get_engines(struct i915_gem_context *ctx,
        struct i915_context_param_engines __user *user;
        struct i915_gem_engines *e;
        size_t n, count, size;
+       bool user_engines;
        int err = 0;
 
-       err = mutex_lock_interruptible(&ctx->engines_mutex);
-       if (err)
-               return err;
+       e = __context_engines_await(ctx, &user_engines);
+       if (!e)
+               return -ENOENT;
 
-       e = NULL;
-       if (i915_gem_context_user_engines(ctx))
-               e = __copy_engines(i915_gem_context_engines(ctx));
-       mutex_unlock(&ctx->engines_mutex);
-       if (IS_ERR_OR_NULL(e)) {
+       if (!user_engines) {
+               i915_sw_fence_complete(&e->fence);
                args->size = 0;
-               return PTR_ERR_OR_ZERO(e);
+               return 0;
        }
 
        count = e->num_engines;
@@ -1934,7 +1911,7 @@ get_engines(struct i915_gem_context *ctx,
        args->size = size;
 
 err_free:
-       free_engines(e);
+       i915_sw_fence_complete(&e->fence);
        return err;
 }