#2137 web: the Monitor page headlines the PCIe max capability as the link speed - a downgraded link shows "Gen3 · idle Gen1"

Beschreibung

## What is wrong

The Monitor page's PCIe metric headlines the link's **capability**, not the link's **speed**, and describes a below-capability link as idle power saving:

```js
const gen = hw.gpu_pcie_gen_max || hw.gpu_pcie_gen;
setMetric("pcie", gen ? `Gen${gen}` : null, ..., ` · idle Gen${hw.gpu_pcie_gen}` ...)
```

So a downgraded link shows as "Gen3 · idle Gen1". That reads as "the link is Gen3, currently idling at Gen1" - but on a link whose Gen3 training failed, the link **never** reaches Gen3 under load either, and "idle" is exactly the wrong word: the link is downgraded, not resting.

## Expected / Actual

**Expected:** the PCIe metric shows the link's current generation, with the capability as context.
**Actual:** it shows the capability as the headline (`Gen3`) and labels a below-capability link as idle (` · idle Gen1`) - on a downgraded link, idle power saving is exactly what is *not* happening.

## Why it matters (a real case)

Found while measuring the PCIe tier for the prefix-reuse series in #2099. This GTX 1080 Ti box: `LnkSta: Speed 2.5GT/s (downgraded), Width x16` on both the card and the root port (`LnkCap 8GT/s`, `Target 8GT/s`), so the link never leaves Gen1. Root cause found later (and worth recording): a leftover driver option, `NVreg_RegistryDwords="...;RmDisableGen2LinkRetraining=1"` in `/etc/modprobe.d/nvidia.conf`, suppresses link speed retraining outright - `LnkSta2` shows the root port's equalization completed while the card's never ran (`PerformEqu=0`, the request left pending), which is "driver never starts it", not "signal fails". Measured over a 171 s sustained cold prefill (147 s of >2 GB/s streaming):

- 8,859 link-gen samples (sub-second, idle baseline included): Gen 1 at **every** sample, never >= 3
- `gpu_pcie_rx_mb` peak 3,191 MB/s - pinned at the Gen1 x16 practical ceiling (~3.2 GB/s)
- the Monitor page nevertheless showed **"Gen3 · idle Gen1"** the whole time

On this machine the PCIe tier is the prefill bottleneck (81% duty at the Gen1 ceiling), and the one number that would have pointed at it was displayed as fine. The telemetry data is already correct (`gpu_pcie_gen` vs `gpu_pcie_gen_max`); only the rendering picks the wrong one as the headline.

## Suggested fix

Headline the **current** generation and keep the capability in the note with neutral wording (one sample cannot tell idle power-saving downtrain from a permanent downgrade):

```js
const cur = hw.gpu_pcie_gen, gen = hw.gpu_pcie_gen_max || cur;
setMetric("pcie", (cur || gen) ? `Gen${cur || gen}` : null, ...,
          ... + (cur && gen && cur < gen ? ` · below its Gen${gen} capability` : ""));
```

We run this on the box here (installed copy) and can send it as a PR - it is a three-line change in `serve/web/app.js`. A further refinement if wanted: when recent history shows the link below capability **under load** (say `gpu_pcie_rx_mb` above some threshold while `gpu_pcie_gen` stays below max), the note could say "downgraded" instead, which is the case worth acting on.



## How to verify the fix

Hardware-independent: feed the metric renderer `hw = {gpu_pcie_gen: 1, gpu_pcie_gen_max: 3, gpu_pcie_width: 16}` and check it renders `Gen1` (with the capability in the note), not `Gen3`. On a healthy link the two renderings agree, which is why the wrong one went unnoticed.