linux-kernel - [RFC] drm/msm: Boost on waits

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Message-Id: <20221104155229.528193-1-robdclark@gmail.com>
Date:   Fri,  4 Nov 2022 08:52:29 -0700
From:   Rob Clark <robdclark@...il.com>
To:     dri-devel@...ts.freedesktop.org
Cc:     freedreno@...ts.freedesktop.org, linux-arm-msm@...r.kernel.org,
        Rob Clark <robdclark@...omium.org>,
        Rob Clark <robdclark@...il.com>,
        Abhinav Kumar <quic_abhinavk@...cinc.com>,
        Dmitry Baryshkov <dmitry.baryshkov@...aro.org>,
        Sean Paul <sean@...rly.run>, David Airlie <airlied@...il.com>,
        Daniel Vetter <daniel@...ll.ch>,
        linux-kernel@...r.kernel.org (open list)
Subject: [RFC] drm/msm: Boost on waits

From: Rob Clark <robdclark@...omium.org>

Minimize interactive latency by boosting frequency when userspace is
waiting on the GPU to finish.

Signed-off-by: Rob Clark <robdclark@...omium.org>
---
I did contemplate also boosting on dma_fence_wait(), but (a) that would
require some extra plumbing thru gpu-sched, (b) that only captures a
sub-set of wait-on-dma-fence patterns, and (c) waiting on a dma-fence
doesn't always imply urgency (for ex, virglrenderer poll()ing on a dma-
fence to know when to send a fence irq to VM guest).  But the driver
WAIT_FENCE and CPU_PREP ioctls map to things like glFinish() where it
is pretty clear that there is something wishing the GPU would finish
sooner.

 drivers/gpu/drm/msm/msm_drv.c         | 7 +++++--
 drivers/gpu/drm/msm/msm_gem.c         | 6 ++++++
 drivers/gpu/drm/msm/msm_gpu_devfreq.c | 2 +-
 3 files changed, 12 insertions(+), 3 deletions(-)

diff --git a/drivers/gpu/drm/msm/msm_drv.c b/drivers/gpu/drm/msm/msm_drv.c
index c3b77b44b2aa..017a512982a2 100644
--- a/drivers/gpu/drm/msm/msm_drv.c
+++ b/drivers/gpu/drm/msm/msm_drv.c
@@ -894,7 +894,7 @@ static int msm_ioctl_gem_info(struct drm_device *dev, void *data,
 }
 
 static int wait_fence(struct msm_gpu_submitqueue *queue, uint32_t fence_id,
-		      ktime_t timeout)
+		      ktime_t timeout, struct msm_gpu *gpu)
 {
 	struct dma_fence *fence;
 	int ret;
@@ -924,6 +924,9 @@ static int wait_fence(struct msm_gpu_submitqueue *queue, uint32_t fence_id,
 	if (!fence)
 		return 0;
 
+	if (!dma_fence_is_signaled(fence))
+		msm_devfreq_boost(gpu, 2);
+
 	ret = dma_fence_wait_timeout(fence, true, timeout_to_jiffies(&timeout));
 	if (ret == 0) {
 		ret = -ETIMEDOUT;
@@ -956,7 +959,7 @@ static int msm_ioctl_wait_fence(struct drm_device *dev, void *data,
 	if (!queue)
 		return -ENOENT;
 
-	ret = wait_fence(queue, args->fence, to_ktime(args->timeout));
+	ret = wait_fence(queue, args->fence, to_ktime(args->timeout), priv->gpu);
 
 	msm_submitqueue_put(queue);
 
diff --git a/drivers/gpu/drm/msm/msm_gem.c b/drivers/gpu/drm/msm/msm_gem.c
index 1dee0d18abbb..fbda0e3a94f8 100644
--- a/drivers/gpu/drm/msm/msm_gem.c
+++ b/drivers/gpu/drm/msm/msm_gem.c
@@ -846,6 +846,12 @@ int msm_gem_cpu_prep(struct drm_gem_object *obj, uint32_t op, ktime_t *timeout)
 		op & MSM_PREP_NOSYNC ? 0 : timeout_to_jiffies(timeout);
 	long ret;
 
+	if (!dma_resv_test_signaled(obj->resv, dma_resv_usage_rw(write))) {
+		struct msm_drm_private *priv = obj->dev->dev_private;
+
+		msm_devfreq_boost(priv->gpu, 2);
+	}
+
 	ret = dma_resv_wait_timeout(obj->resv, dma_resv_usage_rw(write),
 				    true,  remain);
 	if (ret == 0)
diff --git a/drivers/gpu/drm/msm/msm_gpu_devfreq.c b/drivers/gpu/drm/msm/msm_gpu_devfreq.c
index 85c443a37e4e..025940eb08d1 100644
--- a/drivers/gpu/drm/msm/msm_gpu_devfreq.c
+++ b/drivers/gpu/drm/msm/msm_gpu_devfreq.c
@@ -305,7 +305,7 @@ void msm_devfreq_boost(struct msm_gpu *gpu, unsigned factor)
 	struct msm_gpu_devfreq *df = &gpu->devfreq;
 	uint64_t freq;
 
-	if (!has_devfreq(gpu))
+	if (!gpu || !has_devfreq(gpu))
 		return;
 
 	freq = get_freq(gpu);
-- 
2.38.1