diff options
| author | Chris Wilson <chris@chris-wilson.co.uk> | 2016-07-04 08:08:35 +0100 |
|---|---|---|
| committer | Chris Wilson <chris@chris-wilson.co.uk> | 2016-07-04 08:18:22 +0100 |
| commit | df4ba5099f80dac5f822c22937c37860ddd8e434 (patch) | |
| tree | 266ab7a41ad98b7d09eb702b993d7f1edfa164ad /drivers/gpu | |
| parent | 0e6883b043754a44a682a8f8393862e0ef0490dc (diff) | |
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')
| -rw-r--r-- | drivers/gpu/drm/i915/i915_gem.c | 15 |
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); |