Chris Wilson <ch...@chris-wilson.co.uk> writes:
> Now that we can peek at GEM->engines[] and obtain a reference to them
> using RCU, do so for instances where we can safely iterate the
> potentially old copy of the engines. For setting, we can do this when we
> know the engine properties are copied over before swapping, so we know
> the new engines already have the global property and we update the old
> before they are discarded. For reading, we only need to be safe; as we
> do so on behalf of the user, their races are their own problem.
>
> Signed-off-by: Chris Wilson <ch...@chris-wilson.co.uk>
Reviewed-by: Mika Kuoppala <mika.kuopp...@linux.intel.com>
> ---
> drivers/gpu/drm/i915/gem/i915_gem_context.c | 59 +++++++++++----------
> 1 file changed, 31 insertions(+), 28 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/gem/i915_gem_context.c
> b/drivers/gpu/drm/i915/gem/i915_gem_context.c
> index 50e7580f9337..2b6dd08de6f1 100644
> --- a/drivers/gpu/drm/i915/gem/i915_gem_context.c
> +++ b/drivers/gpu/drm/i915/gem/i915_gem_context.c
> @@ -757,21 +757,46 @@ __create_context(struct drm_i915_private *i915)
> return ERR_PTR(err);
> }
>
> +static inline struct i915_gem_engines *
> +__context_engines_await(const struct i915_gem_context *ctx)
> +{
> + struct i915_gem_engines *engines;
> +
> + rcu_read_lock();
> + do {
> + engines = rcu_dereference(ctx->engines);
> + GEM_BUG_ON(!engines);
> +
> + 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 int
> context_apply_all(struct i915_gem_context *ctx,
> int (*fn)(struct intel_context *ce, void *data),
> void *data)
> {
> struct i915_gem_engines_iter it;
> + struct i915_gem_engines *e;
> struct intel_context *ce;
> int err = 0;
>
> - for_each_gem_engine(ce, i915_gem_context_lock_engines(ctx), it) {
> + e = __context_engines_await(ctx);
> + for_each_gem_engine(ce, e, it) {
> err = fn(ce, data);
> if (err)
> break;
> }
> - i915_gem_context_unlock_engines(ctx);
> + i915_sw_fence_complete(&e->fence);
>
> return err;
> }
> @@ -786,11 +811,13 @@ static int __apply_ppgtt(struct intel_context *ce, void
> *vm)
> static struct i915_address_space *
> __set_ppgtt(struct i915_gem_context *ctx, struct i915_address_space *vm)
> {
> - struct i915_address_space *old = i915_gem_context_vm(ctx);
> + struct i915_address_space *old;
>
> + old = rcu_replace_pointer(ctx->vm,
> + i915_vm_open(vm),
> + lockdep_is_held(&ctx->mutex));
> GEM_BUG_ON(old && i915_vm_is_4lvl(vm) != i915_vm_is_4lvl(old));
>
> - rcu_assign_pointer(ctx->vm, i915_vm_open(vm));
> context_apply_all(ctx, __apply_ppgtt, vm);
>
> return old;
> @@ -1069,30 +1096,6 @@ static void cb_retire(struct i915_active *base)
> kfree(cb);
> }
>
> -static inline struct i915_gem_engines *
> -__context_engines_await(const struct i915_gem_context *ctx)
> -{
> - struct i915_gem_engines *engines;
> -
> - rcu_read_lock();
> - do {
> - engines = rcu_dereference(ctx->engines);
> - if (unlikely(!engines))
> - break;
> -
> - 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;
> -}
> -
> I915_SELFTEST_DECLARE(static intel_engine_mask_t
> context_barrier_inject_fault);
> static int context_barrier_task(struct i915_gem_context *ctx,
> intel_engine_mask_t engines,
> --
> 2.20.1
>
> _______________________________________________
> Intel-gfx mailing list
> Intel-gfx@lists.freedesktop.org
> https://lists.freedesktop.org/mailman/listinfo/intel-gfx
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