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drm/i915/execlists: Assert there are no simple cycles in the dependencies 

The dependency chain must be an acyclic graph. This is checked by the
swfence, but for sanity, also do a simple check that we do not corrupt
our list iteration in execlists_schedule() by a shallow dependency
cycle.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: Michał Winiarski <michal.winiarski@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20180102151235.3949-10-chris@chris-wilson.co.uk
This commit is contained in:
Chris Wilson 2018-01-02 15:12:26 +00:00
parent 83cc84c5a8
commit ce01b17377
1 changed files with 8 additions and 3 deletions
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11
drivers/gpu/drm/i915/intel_lrc.c
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@ -1011,7 +1011,8 @@ static void execlists_schedule(struct drm_i915_gem_request *request, int prio)
stack.signaler = &request->priotree;
list_add(&stack.dfs_link, &dfs);
/* Recursively bump all dependent priorities to match the new request.
/*
* Recursively bump all dependent priorities to match the new request.
*
* A naive approach would be to use recursion:
* static void update_priorities(struct i915_priotree *pt, prio) {
@ -1031,12 +1032,15 @@ static void execlists_schedule(struct drm_i915_gem_request *request, int prio)
list_for_each_entry_safe(dep, p, &dfs, dfs_link) {
struct i915_priotree *pt = dep->signaler;
/* Within an engine, there can be no cycle, but we may
/*
* Within an engine, there can be no cycle, but we may
* refer to the same dependency chain multiple times
* (redundant dependencies are not eliminated) and across
* engines.
*/
list_for_each_entry(p, &pt->signalers_list, signal_link) {
GEM_BUG_ON(p == dep); /* no cycles! */
if (i915_priotree_signaled(p->signaler))
continue;
@ -1048,7 +1052,8 @@ static void execlists_schedule(struct drm_i915_gem_request *request, int prio)
list_safe_reset_next(dep, p, dfs_link);
}
/* If we didn't need to bump any existing priorities, and we haven't
/*
* If we didn't need to bump any existing priorities, and we haven't
* yet submitted this request (i.e. there is no potential race with
* execlists_submit_request()), we can set our own priority and skip
* acquiring the engine locks.