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Pro Max 16 Plus MB16250, processor-side PCIe implementation
I am starting a new thread to focus specifically on the processor-side PCIe implementation and platform warm-up behavior on the Dell Pro Max 16 Plus (MB16250), following up on my previous baseline inquiry.
Processor warmup performance changes - MB16250Investigating Host-Side Rx Margin Variance & Processor Warm-Up Behavior
My current investigation centers on the CPU/host-side PCIe path because the weaker timing margins I have observed are located at the host-side receiver, Rx(A). During recent hardware isolation testing, I observed significant changes in measured PCIe lane margins on this path—moving from sub-threshold/Fail results up to tool-graded Perfect results on the exact same machine—depending on platform configuration and thermal state.
Working Hypothesis & Technical Scope
The processor-side PCIe path is currently my primary focus, but it is important to clarify the boundaries of this finding:
Host Receiver Scope: Measuring a host-side receiver evaluates the complete signal delivered by the endpoint through the motherboard channel. It evaluates the entire host path rather than isolating the CPU silicon alone.
Open Hypotheses: Mechanisms like cold solder joints, CPU power delivery, silicon/firmware power-state management, and platform-level interactions remain unverified hypotheses.
Not an Isolated Silicon Defect: These results do not establish a conventional processor compute failure or a defect affecting an entire Intel processor generation.
Key Isolation Findings & Chronology
1. Original Configuration (BE200 WLAN + SSD Installed)
Host-Side Receiver [Rx(A), GPU Lane 5]: Measured ~7.81 ps (LIM/LIM), showing timing error boundaries reached in both sweep directions.
SSD-Side Receiver [Rx(F), Lane 1]: Measured ~9.42 ps against a tool minimum threshold of 9.38 ps.
Note: The SSD-side and processor-side measurements represent opposite signal directions.
2. BE200 WLAN Card Removed (SSD also briefly removed)
With the WLAN adapter removed, the host-side GPU receiver margin repeatedly produced a substantial improvement:
GPU Rx(A), Lane 5: 12.50 ps (THR/THR).
Note on THR status: The tool reached its maximum configured sweep limit without finding an error boundary. This indicates a strong margin exceeding 12.50 ps, rather than a hard limit at that number.
3. SSD Reintroduced to Original M.2 Slot (BE200 Still Absent)
GPU Rx(A), Lane 5: Maintained the improved 12.50 ps (THR/THR) result.
SSD Rx(F), Lane 1: Remained at 9.18 ps.
Observation: Reinstalling the SSD did not undo the improved host-side GPU margin, though removing the WLAN adapter did not eliminate the endpoint-side low margin in the primary slot.
4. SSD Shifted to Secondary Slot (SSD3, BE200 Still Absent)
An initial run on SSD3 showed an initial sub-threshold result on Lane 2 (~8.69 ps). Without any physical slot changes, a subsequent run on the exact same setup yielded a full-pass result across all four lanes as the platform warmed up:
| SSD Receiver Lane | Reported Timing Width | Utility Grade |
| Lane 0 | 14.63 ps | Perfect |
| Lane 1 | 13.39 ps | Perfect |
| Lane 2 | 11.16 ps | Perfect |
| Lane 3 | 12.65 ps | Perfect |
The GPU host-side receiver remained at 12.50 ps (THR/THR).
Observation: The lane-margin grade changed dynamically between consecutive runs on the same physical topology, moving from sub-threshold to well above the recommended 10.16 ps criterion.
5. Conventional Processor Diagnostics vs. PCIe Lane Margining
To establish whether this behavior aligns with standard CPU failures, I ran a series of diagnostic and telemetry controls.
In a stripped-down USB environment (SSD and BE200 absent), the system passed conventional testing:
Intel Processor Diagnostic Tool (Windows USB): Passed with zero failures.
stress-ng (Ubuntu): All 24 CPU workers completed an all-CPU stress test with 0 failures.
Intel PCM (Performance Counter Monitor): Collected processor performance-counter telemetry (per-core activity, frequency, C-states, and package energy) before and after load tests.
Intel PMC / debugfs Telemetry: Observed software-visible platform power management, PCIe PHY, and PLL states over a 300-second baseline. Several state indicators changed without corresponding AER increments.
pciutils / pcilmr: Used for PCIe Lane Margining at the Receiver. This is where the host-side and endpoint-side margin variations were captured.
lspci / Linux AER Telemetry: Tracked PCIe topology, negotiated link width/speed, and AER status around controlled tests.
NVIDIA DCGM / dcgmi: Monitored GPU-side diagnostics (noting one attempt skipped the PCIe diagnostic).
NVMe Self-Tests & GPU Load Controls: Completed without producing new AER log increments.
Distinction: Standard CPU compute diagnostics (like IPDT or stress-ng) test execution units and core stability. They do not certify host PCIe PHY receiver tolerance, package interconnect signal integrity, REFCLK quality, solder joint integrity, or dynamic firmware power-state behavior. That is why the processor path remains my primary focus despite passing standard CPU diagnostic suites.
What Is Established vs. Unverified Hypotheses
What is established: Host-side receiver margins on this platform exhibit significant, repeatable variance across device removal states and run-to-run warm-up cycles.
What remains unverified:
Thermal Correlation: While margins improve across consecutive runs as the processor warms up, I have not yet performed controlled temperature-chamber experiments to prove direct thermal dependency.
WLAN Causality: Removing the BE200 alters PCIe root-port power states, clocks, and firmware behavior; it does not prove direct RF/EMI interference.
Physical Mechanisms: Cold solder joints, CPU power delivery fluctuations, silicon errata, and board-level interactions remain competing hypotheses rather than proven causes.
(edited)
