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authorChris Wilson <chris@chris-wilson.co.uk>2016-07-04 08:08:35 +0100
committerChris Wilson <chris@chris-wilson.co.uk>2016-07-04 08:18:22 +0100
commitdf4ba5099f80dac5f822c22937c37860ddd8e434 (patch)
tree266ab7a41ad98b7d09eb702b993d7f1edfa164ad /drivers/gpu/drm/i915/i915_gem.c
parent0e6883b043754a44a682a8f8393862e0ef0490dc (diff)
downloadlinux-stericsson-df4ba5099f80dac5f822c22937c37860ddd8e434.tar.gz
drm/i915: Add background commentary to "waitboosting"
Describe the intent of boosting the GPU frequency to maximum before waiting on the GPU. RPS waitboosting was introduced with commit b29c19b64528 ("drm/i915: Boost RPS frequency for CPU stalls") but lacked a concise comment in the code to explain itself. Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch> Link: http://patchwork.freedesktop.org/patch/msgid/1467616119-4093-5-git-send-email-chris@chris-wilson.co.uk
Diffstat (limited to 'drivers/gpu/drm/i915/i915_gem.c')
-rw-r--r--drivers/gpu/drm/i915/i915_gem.c15
1 files changed, 15 insertions, 0 deletions
diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c
index 037b26e2a960..b11884d656cf 100644
--- a/drivers/gpu/drm/i915/i915_gem.c
+++ b/drivers/gpu/drm/i915/i915_gem.c
@@ -1462,6 +1462,21 @@ int __i915_wait_request(struct drm_i915_gem_request *req,
trace_i915_gem_request_wait_begin(req);
+ /* This client is about to stall waiting for the GPU. In many cases
+ * this is undesirable and limits the throughput of the system, as
+ * many clients cannot continue processing user input/output whilst
+ * blocked. RPS autotuning may take tens of milliseconds to respond
+ * to the GPU load and thus incurs additional latency for the client.
+ * We can circumvent that by promoting the GPU frequency to maximum
+ * before we wait. This makes the GPU throttle up much more quickly
+ * (good for benchmarks and user experience, e.g. window animations),
+ * but at a cost of spending more power processing the workload
+ * (bad for battery). Not all clients even want their results
+ * immediately and for them we should just let the GPU select its own
+ * frequency to maximise efficiency. To prevent a single client from
+ * 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)
gen6_rps_boost(req->i915, rps, req->emitted_jiffies);