# tt_pci_device_count

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## Name

### Prometheus Metric Name

```
tt_pci_device_count
```

### Metric Path (tt-telemetry)

Schema:

```
{hostname}/tt_pci_device_count
```

Example path:

```
bh-glx-c09u02/tt_pci_device_count
```

## Description

The number of Tenstorrent devices present on the host's PCI bus. It is counted by walking `/sys/bus/pci/devices/` and reading the `vendor` file in each device directory, counting those whose value matches the Tenstorrent PCI vendor ID `0x1e52`. This is the equivalent of `lspci | grep 1e52 | wc -l`, computed by reading sysfs directly rather than by spawning a subprocess.

The Linux PCI subsystem enumerates the bus at boot and publishes a directory for every function it finds, **whether or not a driver binds to it**. This metric therefore reports the hardware population as the kernel sees it, before and independently of any attempt by the Tenstorrent kernel-mode driver (KMD) to claim the devices. Devices are matched on vendor ID only, so the count covers all Tenstorrent ASIC generations (Wormhole, Blackhole, and future device IDs) without needing to be updated.

This is the key distinction from [tt_chip_count](tt_chip_count.md), which counts the character devices the KMD created (via `PCIDevice::enumerate_devices()`) and so only sees devices the driver successfully bound to. Comparing the two isolates where a fault lies:

|Observation|Interpretation|
|---|---|
|`tt_pci_device_count == tt_chip_count`|Healthy: every device on the bus was claimed by the driver.|
|`tt_pci_device_count > tt_chip_count`|The card is physically present and its PCIe link is trained, but the driver did not claim it. Suspect the KMD (not loaded, version mismatch, bind failure) rather than the hardware.|
|`tt_pci_device_count` below the expected number for the host|The card is not visible to the kernel at all. Suspect hardware: card not seated, PCIe link down, or the device fell off the bus.|

This is a host-level metric (not scoped to a tray or chip path). It is created when device telemetry collection is enabled, and its value is refreshed on every collection cycle. It is driver-independent: it reads sysfs directly, requires neither UMD initialization nor an open device, and so persists across warm resets and continues to report a meaningful value when driver initialization fails outright. PCI devices are not namespaced and container runtimes mount `/sys` by default, so the count is correct when tt-telemetry runs inside a container. If `/sys/bus/pci/devices/` cannot be enumerated, a warning is logged and the value is reported as `0`.

## Values

**Type:** Unsigned Integer

**Units:** None

**Allowable values:** Non-negative integer representing the number of Tenstorrent PCI functions the kernel has enumerated (for example `4` on a four-card host, or `0` on a host with no Tenstorrent hardware or with sysfs unavailable).

## Related Metrics

|Metric|Description|
|---|---|
|[tt_chip_count](tt_chip_count.md)|Number of chips the driver actually claimed; compare against `tt_pci_device_count` to distinguish a driver bind failure from missing hardware.|
|[tt_expected_chip_count](tt_expected_chip_count.md)|Expected chip count on Galaxy hosts (32); the reference value both counts should match.|
|[tt_driver_initialized](tt_driver_initialized.md)|Whether the device driver is initialized. `tt_pci_device_count` is assessed independently of driver initialization.|
|[tt_pcie_link_alive](tt_pcie_link_alive.md)|Per-chip PCIe liveness, as probed through the driver by host-issued reads.|

## Prometheus Labels

|Label Name|Value|
|---|---|
|hostname|The host from which the metric was collected.|
|hall|The datacenter hall where the host is located. Sourced from the Factory System Descriptor (FSD).|
|aisle|The datacenter aisle where the host is located. Sourced from the Factory System Descriptor (FSD).|
|rack|The rack number where the host is located. Sourced from the Factory System Descriptor (FSD).|
|shelf_u|The shelf U position in the rack where the host is located. Sourced from the Factory System Descriptor (FSD).|