Bing Nsight Performance Analysis

[bryanedds]

Analyze my performance and potential bottlenecks when the throughputs are as such -

l1tex throughput = 34.3%
sm throughput = 28.0%
screen pipe throughput = 20.6%
l2 throughput = 18.4%
vram throughput = 15.3%
pcie throughput = 9.7%
world pipe throughput = 7.8%
front end throughput = 3.3%
rtcore throughput = 0%

Let's break down what these throughput numbers might be telling you about your rendering performance:

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1. Moderate Utilization in the GPU’s Compute & Texture Units

• L1tex Throughput at 34.3% & SM Throughput at 28.0%
  These figures suggest that your shader execution units (SMs) and texture processing units (L1tex) are moderately active. They aren’t hitting their maximum capacity, which implies that your shader computations and texture fetches are proceeding but not fully loading the pipeline. This can be a good thing if your workload doesn’t demand maximal compute power. Conversely, if you were expecting higher overall GPU utilization, these moderate percentages might indicate that the rest of your pipeline isn’t being kept busy with enough work.

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2. Screen, Memory, and Data Path Throughputs

• Screen Pipe Throughput at 20.6%
  This value typically gauges the work related to final pixel output, such as blending and post-processing. A 20.6% usage indicates that the display-related processing is active but not saturating the unit.

• L2 Throughput at 18.4% & VRAM Throughput at 15.3%
  These numbers tell you that the memory subsystem on the GPU—both the intermediate shared cache (L2) and the actual VRAM—is only moderately stressed. In other words, your workload isn’t heavily bottlenecked by memory bandwidth or cache misses.

• PCIe Throughput at 9.7%
  Data transfer between the host (CPU) and GPU is relatively light. This is expected in workloads where most of the heavy lifting happens on the GPU itself. It indicates that the interconnect isn’t the primary limiting factor.

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3. Potential Bottlenecks in the Front-End and Work Submission

• World Pipe Throughput at 7.8% & Front End Throughput at 3.3%
  The “world pipe” generally refers to stages responsible for setting up geometry, transformations, or even certain culling operations. Meanwhile, the front-end is crucial for gathering, issuing, and dispatching draw calls from the CPU side into the GPU pipeline. A very low front-end throughput (3.3%) is a red flag—it suggests that the GPU is waiting on work to be fed into the system. This can happen due to:

  • CPU or Driver Limitations: Your CPU might not be submitting draw calls fast enough, or there may be excessive state changes or other overhead in your OpenGL code.
  • Inefficient Batching: Excessive small or fragmented draw calls may lead to underutilization of the command assembly, leaving many parts of the GPU idle.

  This could be the primary bottleneck: even though the shader units and texture units are moderately active, the overall pipeline isn’t receiving a steady or large enough stream of commands to push them harder.

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4. RT Core Throughput at 0%

• RT Core Throughput at 0%
  This simply indicates that no ray-tracing work is being performed. Unless your application is targeting ray-tracing effects, this isn’t a concern—it shows that the specialized RT cores are idle because they aren’t being asked to process any ray-tracing workload.

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Overall Analysis & Recommendations

• GPU is Not Saturated:
  None of the major units (SMs, texture caches, memory interfaces) are pushed near their limits. This overall low-to-moderate utilization across the board suggests that your GPU’s backend can handle more work than it’s currently receiving.

• The Primary Bottleneck May Lie in Work Submission:
  The very low front-end throughput (3.3%) is a strong indicator that the pipeline is “starved” for instructions—most likely due to limitations on the CPU side or inefficient draw call management in your OpenGL rendering code. Even if your shader and texture units are ready to work, they might be waiting on the front-end to feed them new commands.

• Improvement Suggestions:

  • Optimize Draw Call Batching: Reduce the number of small draw calls by grouping similar objects or state changes together.
  • Minimize State Changes: Avoid unnecessary shader swaps, texture bindings, or other state modifications that could force the CPU and driver to slow down command submission.
  • Profile CPU Performance: Use both GPU (Nsight, RenderDoc) and CPU profiling tools to see if your CPU is a limiting factor in dispatching rendering commands.
  • Examine Scene Complexity: If possible, check whether the scene management or culling methods might be causing the CPU to underfeed the GPU.

In summary, while your compute and memory-related units are under moderate load (suggesting they’re not bottlenecks), the very low front-end and world pipe throughputs hint at an issue upstream—most likely tied to how work is being issued to the GPU. Addressing the CPU-side submission inefficiencies could lead to a better-balanced pipeline and improved overall performance.