[PATCH 50/92] drm/i915: Disable waitboosting for fence_wait()

Chris Wilson chris at chris-wilson.co.uk
Thu May 26 10:11:56 UTC 2016


We want to restrict waitboosting to known process contexts, where we can
track which clients are receiving waitboosts and prevent excessive power
wasting. For fence_wait() we do not have any client tracking and so that
leaves it open to abuse.

Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
---
 drivers/gpu/drm/i915/i915_gem_request.c | 7 ++++---
 drivers/gpu/drm/i915/i915_gem_request.h | 1 +
 2 files changed, 5 insertions(+), 3 deletions(-)

diff --git a/drivers/gpu/drm/i915/i915_gem_request.c b/drivers/gpu/drm/i915/i915_gem_request.c
index f5824852aefb..d7feaab25590 100644
--- a/drivers/gpu/drm/i915/i915_gem_request.c
+++ b/drivers/gpu/drm/i915/i915_gem_request.c
@@ -74,7 +74,7 @@ static signed long i915_fence_wait(struct fence *fence,
 
 	ret = __i915_wait_request(to_i915_request(fence),
 				  interruptible, timeout,
-				  NULL);
+				  NO_WAITBOOST);
 	if (ret == -ETIME)
 		return 0;
 
@@ -627,7 +627,7 @@ int __i915_wait_request(struct drm_i915_gem_request *req,
 	 * forcing the clocks too high for the whole system, we only allow
 	 * each client to waitboost once in a busy period.
 	 */
-	if (INTEL_INFO(req->i915)->gen >= 6)
+	if (!IS_ERR(rps) && INTEL_INFO(req->i915)->gen >= 6)
 		gen6_rps_boost(req->i915, rps, req->emitted_jiffies);
 
 	/* Optimistic spin for the next ~jiffie before touching IRQs */
@@ -701,7 +701,8 @@ complete:
 			*timeout = 0;
 	}
 
-	if (rps && req->fence.seqno == req->engine->last_submitted_seqno) {
+	if (!IS_ERR_OR_NULL(rps) &&
+	    req->fence.seqno == req->engine->last_submitted_seqno) {
 		/* The GPU is now idle and this client has stalled.
 		 * Since no other client has submitted a request in the
 		 * meantime, assume that this client is the only one
diff --git a/drivers/gpu/drm/i915/i915_gem_request.h b/drivers/gpu/drm/i915/i915_gem_request.h
index 7dbd5b338671..f01100b0b61e 100644
--- a/drivers/gpu/drm/i915/i915_gem_request.h
+++ b/drivers/gpu/drm/i915/i915_gem_request.h
@@ -204,6 +204,7 @@ void __i915_add_request(struct drm_i915_gem_request *req,
 	__i915_add_request(req, NULL, false)
 
 struct intel_rps_client;
+#define NO_WAITBOOST ERR_PTR(-1)
 
 int __i915_wait_request(struct drm_i915_gem_request *req,
 			bool interruptible,
-- 
2.8.1



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