[Intel-gfx] [PATCH 1/3] RFM drm/i915: Boost RPS frequency for CPU stalls

[Chris Wilson]

If we encounter a situation where the CPU blocks waiting for results
from the GPU, give the GPU a kick to boost its the frequency.

This should work to reduce user interface stalls and to quickly promote
mesa to high frequencies - but the cost is that our requested frequency
stalls high (as we do not idle for long enough before rc6 to start
reducing frequencies, nor are we aggressive at down clocking an
underused GPU). However, this should be mitigated by rc6 itself powering
off the GPU when idle, and that energy use is dependent upon the workload
of the GPU in addition to its frequency (e.g. the math or sampler
functions only consume power when used). Still, this is likely to
adversely affect light workloads.

Stéphane raised the concern that this will punish good applications and
reward bad applications - but due to the nature of how mesa performs its
client throttling, I believe all mesa applications will be roughly
equally affected.

RFM - request for measurement!

Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
Cc: Kenneth Graunke <kenneth at whitecape.org>
Cc: Stéphane Marchesin <stephane.marchesin at gmail.com>
Cc: "Meng, Mengmeng" <mengmeng.meng at intel.com>
Cc: "Zhuang, Lena" <lena.zhuang at intel.com>
---
 drivers/gpu/drm/i915/i915_gem.c | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c
index 091bb553..8ef3559 100644
--- a/drivers/gpu/drm/i915/i915_gem.c
+++ b/drivers/gpu/drm/i915/i915_gem.c
@@ -1106,6 +1106,15 @@ static int __wait_seqno(struct intel_ring_buffer *ring, u32 seqno,
 	if (WARN_ON(!ring->irq_get(ring)))
 		return -ENODEV;
 
+	if (dev_priv->info->gen >= 6) {
+		mutex_lock(&dev_priv->rps.hw_lock);
+		if (dev_priv->info->is_valleyview)
+			valleyview_set_rps(dev_priv->dev, dev_priv->rps.max_delay);
+		else
+			gen6_set_rps(dev_priv->dev, dev_priv->rps.max_delay);
+		mutex_unlock(&dev_priv->rps.hw_lock);
+	}
+
 	/* Record current time in case interrupted by signal, or wedged * */
 	getrawmonotonic(&before);
 
-- 
1.8.4.rc3