gallium: add take_ownership param into set_constant_buffer to eliminate atomics

We often do this:
    pipe->set_constant_buffer(pipe, shader, slot, &cb);
    pipe_resource_reference(&cb->buffer, NULL);

That results in atomic increment in set_constant_buffer followed by
atomic decrement after set_constant_buffer. This new interface
eliminates those atomics.

For the case above, this should be used instead:
    pipe->set_constant_buffer(pipe, shader, slot, true, &cb);
    cb->buffer = NULL; // if cb is not a local variable, else do nothing

AMD Zen benefits from this. The perf improvement is ~3% for Viewperf13/Catia.

Reviewed-by: Pierre-Eric Pelloux-Prayer <pierre-eric.pelloux-prayer@amd.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/8298>

1 files changed, 8 insertions, 1 deletions

diff --git a/src/gallium/drivers/nouveau/nvc0/nvc0_state.c b/src/gallium/drivers/nouveau/nvc0/nvc0_state.c
index c44c87bd370..a3a9fd1454f 100644
--- a/src/gallium/drivers/nouveau/nvc0/nvc0_state.c
+++ b/src/gallium/drivers/nouveau/nvc0/nvc0_state.c
@@ -774,6 +774,7 @@ nvc0_cp_state_bind(struct pipe_context *pipe, void *hwcso)
 static void
 nvc0_set_constant_buffer(struct pipe_context *pipe,
                          enum pipe_shader_type shader, uint index,
+                         bool take_ownership,
                          const struct pipe_constant_buffer *cb)
 {
    struct nvc0_context *nvc0 = nvc0_context(pipe);
@@ -802,7 +803,13 @@ nvc0_set_constant_buffer(struct pipe_context *pipe,
 
    if (nvc0->constbuf[s][i].u.buf)
       nv04_resource(nvc0->constbuf[s][i].u.buf)->cb_bindings[s] &= ~(1 << i);
-   pipe_resource_reference(&nvc0->constbuf[s][i].u.buf, res);
+
+   if (take_ownership) {
+      pipe_resource_reference(&nvc0->constbuf[s][i].u.buf, NULL);
+      nvc0->constbuf[s][i].u.buf = res;
+   } else {
+      pipe_resource_reference(&nvc0->constbuf[s][i].u.buf, res);
+   }
 
    nvc0->constbuf[s][i].user = (cb && cb->user_buffer) ? true : false;
    if (nvc0->constbuf[s][i].user) {