From 71895a085879d7bc490611994c7efb156162f33d Mon Sep 17 00:00:00 2001 From: Mika Kuoppala Date: Tue, 17 Jan 2017 17:59:07 +0200 Subject: [PATCH] drm/i915: Add comment how we treat hung contexts Explain in a comment how and why we treat hung context like we do. Cc: Chris Wilson Cc: Tvrtko Ursulin Signed-off-by: Mika Kuoppala Link: http://patchwork.freedesktop.org/patch/msgid/1484668747-9120-7-git-send-email-mika.kuoppala@intel.com Reviewed-by: Chris Wilson Signed-off-by: Chris Wilson --- drivers/gpu/drm/i915/i915_gem.c | 21 +++++++++++++++++++++ 1 file changed, 21 insertions(+) diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c index 3e10e81..d6ec639 100644 --- a/drivers/gpu/drm/i915/i915_gem.c +++ b/drivers/gpu/drm/i915/i915_gem.c @@ -2697,6 +2697,27 @@ static bool i915_gem_reset_request(struct drm_i915_gem_request *request) /* Read once and return the resolution */ const bool guilty = engine_stalled(request->engine); + /* The guilty request will get skipped on a hung engine. + * + * Users of client default contexts do not rely on logical + * state preserved between batches so it is safe to execute + * queued requests following the hang. Non default contexts + * rely on preserved state, so skipping a batch loses the + * evolution of the state and it needs to be considered corrupted. + * Executing more queued batches on top of corrupted state is + * risky. But we take the risk by trying to advance through + * the queued requests in order to make the client behaviour + * more predictable around resets, by not throwing away random + * amount of batches it has prepared for execution. Sophisticated + * clients can use gem_reset_stats_ioctl and dma fence status + * (exported via sync_file info ioctl on explicit fences) to observe + * when it loses the context state and should rebuild accordingly. + * + * The context ban, and ultimately the client ban, mechanism are safety + * valves if client submission ends up resulting in nothing more than + * subsequent hangs. + */ + if (guilty) { i915_gem_context_mark_guilty(request->ctx); skip_request(request); -- 2.7.4