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Refine cross-validation steps and learning outcomes in comparative analysis documentation
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content/learning-paths/servers-and-cloud-computing/memory-subsystem/comparative-analysis.md

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@@ -167,11 +167,11 @@ Peak bandwidth from `peak-bandwidth` shows the system-level memory controller ca
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The credibility of this type of analysis comes from cross-validation. Check that:
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1. Latency steps match cache sizes: the `latency-sweep` boundaries should align with the cache sizes reported by `sysfs` and the TRM.
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2. Bandwidth plateaus match cache sizes: the `bandwidth-sweep` should show transitions at the same data sizes that `latency-sweep` identified.
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3. Peak bandwidth matches documented limits: compare the "All Reads" figure from `peak-bandwidth` against the theoretical peak from `asct system-info`. A well-configured system typically achieves 85-95% of theoretical peak.
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4. Idle loaded latency matches unloaded latency: the lowest-load row from `loaded-latency` should be close to the DRAM latency from `latency-sweep`.
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5. Results are repeatable: run each benchmark at least twice. If results vary by more than 5%, investigate sources of noise (CPU frequency scaling, background processes).
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- Latency steps match cache sizes: the `latency-sweep` boundaries should align with the cache sizes reported by `sysfs` and the TRM.
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- Bandwidth plateaus match cache sizes: the `bandwidth-sweep` should show transitions at the same data sizes that `latency-sweep` identified.
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- Peak bandwidth matches documented limits: compare the "All Reads" figure from `peak-bandwidth` against the theoretical peak from `asct system-info`. A well-configured system typically achieves 85-95% of theoretical peak.
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- Idle loaded latency matches unloaded latency: the lowest-load row from `loaded-latency` should be close to the DRAM latency from `latency-sweep`.
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- Results are repeatable: run each benchmark at least twice. If results vary by more than 5%, investigate sources of noise (CPU frequency scaling, background processes).
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{{% notice Tip %}}
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Check if your system allows you to control CPU frequency scaling during benchmarks for more consistent results:
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The examples here used AWS Graviton instances, but the methodology works on any Arm Linux machine with a NUMA-enabled kernel. To adapt it:
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1. Install ASCT on the target system following the [install guide](/install-guides/asct/).
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2. Run all memory benchmarks: `sudo asct run memory loaded-latency --format=csv --output-dir results_$(hostname)`
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3. Compare with previous systems: `asct diff results_new/ --baseline results_reference/`
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4. Cross-validate: check that latency boundaries, bandwidth plateaus, and peak numbers are consistent with each other and with the hardware documentation.
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- Install ASCT on the target system following the [install guide](/install-guides/asct/).
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- Run all memory benchmarks: `sudo asct run memory loaded-latency --format=csv --output-dir results_$(hostname)`
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- Compare with previous systems: `asct diff results_new/ --baseline results_reference/`
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- Cross-validate: check that latency boundaries, bandwidth plateaus, and peak numbers are consistent with each other and with the hardware documentation.
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## What you've accomplished
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## What you've learned
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In this section you:
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- Identified the topology and cache hierarchy of Arm Linux systems using `sysfs` and `asct system-info`
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- Measured cache and memory latency with the ASCT `latency-sweep` benchmark
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- Measured single-core streaming bandwidth with `bandwidth-sweep`
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- Measured peak system bandwidth with `peak-bandwidth` and the latency-bandwidth tradeoff with `loaded-latency`
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- Compared Graviton2 and Graviton4 to understand how generational improvements in core microarchitecture and memory technology affect real-world performance
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- Developed a portable methodology that works on any Arm Linux system with a single command
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- Developed a portable methodology that works on any Arm Linux system with a single command

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