[PATCH v2] drm/i915: Disable waitboosting for fence_wait()

Chris Wilson
2016-07-15T11:53:37Z

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.

v2: Hide the IS_ERR_OR_NULL testing for special clients

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

diff --git a/drivers/gpu/drm/i915/i915_gem_request.c b/drivers/gpu/drm/i915/i915_gem_request.c
index 6528536878f2..f483e605a715 100644
--- a/drivers/gpu/drm/i915/i915_gem_request.c
+++ b/drivers/gpu/drm/i915/i915_gem_request.c
@@ -70,7 +70,7 @@ static signed long i915_fence_wait(struct fence *fence,

ret = __i915_wait_request(to_request(fence),
interruptible, timeout,
- NULL);
+ NO_WAITBOOST);
if (ret == -ETIME)
return 0;

@@ -642,7 +642,7 @@ 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_GEN(req->i915) >= 6)
+ if (IS_RPS_CLIENT(rps) && INTEL_GEN(req->i915) >= 6)
gen6_rps_boost(req->i915, rps, req->emitted_jiffies);

/* Optimistic spin for the next ~jiffie before touching IRQs */
@@ -713,7 +713,8 @@ complete:
*timeout = 0;
}

- if (rps && req->fence.seqno == req->engine->last_submitted_seqno) {
+ if (IS_RPS_USER(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 6f2c820785f3..0a01d01cac51 100644
--- a/drivers/gpu/drm/i915/i915_gem_request.h
+++ b/drivers/gpu/drm/i915/i915_gem_request.h
@@ -206,6 +206,9 @@ 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)
+#define IS_RPS_CLIENT(p) (!IS_ERR(p))
+#define IS_RPS_USER(p) (!IS_ERR_OR_NULL(p))

int __i915_wait_request(struct drm_i915_gem_request *req,
bool interruptible,
--
2.8.1