What it does
BIG-IP 21.1 rebuilt bigd, the health-monitor daemon, as a single multi-threaded instance able to serve up to 15,000 control-plane monitors, and documented exactly how the automatic thread count is derived from the vCPU count. This tool encodes those two formulas verbatim: enter a vCPU count plus the system type and it returns the thread count the system would derive, the bigd.numprocs manual-override cap, and the monitor ceiling. A bare number computes both formulas side by side.
The two formulas
For hyperthreaded systems, F5's release notes state Number of BigD Threads = (Number of vCPUs × 6) ÷ 10, with the rationale that HT cores run at roughly 60% of a real core's performance. For normal (non-HT) systems the formula is Number of BigD Threads = (Number of vCPUs ÷ 2) − 1. Where a formula yields a fraction (8 vCPUs hyperthreaded gives 4.8), the release notes state no rounding rule, so the tool shows both the exact value and its whole-thread floor and says so plainly. At 2 vCPUs the normal formula's honest result is 0; bigd still runs, so read that edge as minimal threading, not absence.
The override and the ceiling
The db variable bigd.numprocs sets the thread count manually but is capped at the number of available vCPUs; its default 0 means automatic calculation with the formulas above. The multi-threaded daemon supports up to 15,000 control-plane monitors. For sizing context, F5's 21.0 notes recommend keeping bigd at or below 5,000 monitor instances and moving beyond that to In-TMM monitors, which scale to 25,000 with an 8 GB extramb allocation.
Which platforms are hyperthreaded
The formula choice is a platform fact, and F5's own platform documentation settles it. On rSeries, the family splits down the middle: the mid-range and high-end appliances (r5000, r10000, and the r12000 family in F5's sizing tables) run hyperthreading, each Intel core appearing as two vCPUs, while the r2000 and r4000 use a CPU class without hyperthreading and are counted in physical cores only. VELOS is hyperthreaded on both blade types: a tenant's vCPUs are hyperthreads, two per physical core, with BIG-IP tenants using the HT-Split arrangement (K15003) where TMM takes one hyperthread of each core. iSeries and VIPRION also count vCPUs as hyperthreads in F5's sizing language, but neither runs BIG-IP 21.x, so for them the tool shows the mapping as context only. Virtual Edition inherits whatever the hypervisor exposes: check inside the guest (lscpu, Thread(s) per core) and pick the matching formula.
Type the platform straight into the input: 8 r10900 selects the hyperthreaded formula, 16 r4800 the normal one, 22 velos hyperthreaded, 8 ve shows both with the check-your-host note. An explicit ht or normal word always overrides the platform default, for the case where hyperthreading was disabled in firmware.
Worked examples
8 ht yields 4.8 exact, 4 whole threads. 10 ht lands whole at 6. 16 normal gives 7. 40 ht gives 24. 6 alone shows both: 3.6 (floor 3) hyperthreaded, 2 normal.
Provenance
Formulas, cap behavior, and the 15,000 ceiling are verbatim from F5's "New Features in BIG-IP Version 21.1.0" release notes (BigD enhancements for large-scale configurations), fetched 2026-07-08; the 5,000-instance guidance and In-TMM figures are from the 21.0.0 counterpart. The running system's actual thread count is always authoritative.