til: introduce til_frame_plan_t and .cpu_affinity

modules/checkers w/fill_module=$module requires a consistent
mapping of cpu to fragnum since it creates a per-cpu
til_module_context_t for the fill_module.

The existing implementation for threaded rendering maximizes
performance by letting *any* scheduled to run thread advance
fragnum atomically and render the acquired fragnum
indiscriminately.  A side effect of this is any given frame, even
rendered by the same module, will have a random mapping of
cpus/threads to fragnums.

With this change, the simple til_module_t.prepare_frame() API of
returning a bare fragmenter function is changed to instead return
a "frame plan" in til_frame_plan_t.  Right now til_frame_plan_t
just contains the same fragmenter as before, but also has a
.cpu_affinity member for setting if the frame requires a stable
relationship of cpu/thread to fragnum.

Setting .cpu_affinity should be avoided if unnecessary, and that
is the default if you don't mention .cpu_affinity at all when
initializing the plan in the ergonomic manner w/designated
initializers.  This is because the way .cpu_affinity is
implemented will leave threads spinning while they poll for
*their* next fragnum using atomic intrinsics.  There's probably
some room for improvement here, but this is good enough for now
to get things working and correct.

1 files changed, 1 insertions, 1 deletions

diff --git a/src/til_threads.h b/src/til_threads.h
index 6b854f0..329ead9 100644
--- a/src/til_threads.h
+++ b/src/til_threads.h
@@ -7,7 +7,7 @@ typedef struct til_threads_t til_threads_t;
 til_threads_t * til_threads_create();
 void til_threads_destroy(til_threads_t *threads);
 
-void til_threads_frame_submit(til_threads_t *threads, til_fb_fragment_t *fragment, til_fragmenter_t fragmenter, void (*render_fragment_func)(til_module_context_t *context, unsigned ticks, unsigned cpu, til_fb_fragment_t *fragment), til_module_context_t *context, unsigned ticks);
+void til_threads_frame_submit(til_threads_t *threads, til_fb_fragment_t *fragment, til_frame_plan_t *frame_plan, void (*render_fragment_func)(til_module_context_t *context, unsigned ticks, unsigned cpu, til_fb_fragment_t *fragment), til_module_context_t *context, unsigned ticks);
 void til_threads_wait_idle(til_threads_t *threads);
 unsigned til_threads_num_threads(til_threads_t *threads);