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drm/i915: Restore waitboost credit to the synchronous waiter
Ideally, we want to automagically have the GPU respond to the instantaneous load by reclocking itself. However, reclocking occurs relatively slowly, and to the client waiting for a result from the GPU, too late. To compensate and reduce the client latency, we allow the first wait from a client to boost the GPU clocks to maximum. This overcomes the lag in autoreclocking, at the expense of forcing the GPU clocks too high. So to offset the excessive power usage, we currently allow a client to only boost the clocks once before we detect the GPU is idle again. This works reasonably for say the first frame in a benchmark, but for many more synchronous workloads (like OpenCL) we find the GPU clocks remain too low. By noting a wait which would idle the GPU (i.e. we just waited upon the last known request), we can give that client the idle boost credit (for their next wait) without the 100ms delay required for us to detect the GPU idle state. The intention is to boost clients that are stalling in the process of feeding the GPU more work (and who in doing so let the GPU idle), without granting boost credits to clients that are throttling themselves (such as compositors). Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Cc: "Zou, Nanhai" <nanhai.zou@intel.com> Cc: Jesse Barnes <jbarnes@virtuousgeek.org> Reviewed-by: Jesse Barnes <jbarnes@virtuousgeek.org> Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch> Link: http://patchwork.freedesktop.org/patch/msgid/1467616119-4093-4-git-send-email-chris@chris-wilson.co.uk
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@ -1542,6 +1542,22 @@ int __i915_wait_request(struct drm_i915_gem_request *req,
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*timeout = 0;
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}
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if (rps && req->seqno == req->engine->last_submitted_seqno) {
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/* The GPU is now idle and this client has stalled.
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* Since no other client has submitted a request in the
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* meantime, assume that this client is the only one
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* supplying work to the GPU but is unable to keep that
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* work supplied because it is waiting. Since the GPU is
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* then never kept fully busy, RPS autoclocking will
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* keep the clocks relatively low, causing further delays.
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* Compensate by giving the synchronous client credit for
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* a waitboost next time.
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*/
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spin_lock(&req->i915->rps.client_lock);
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list_del_init(&rps->link);
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spin_unlock(&req->i915->rps.client_lock);
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}
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return ret;
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}
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