Skip remaining PCI devices when device 0 is absent on a bus

[jbreitbart]

Summary

• Apply standard PCI enumeration optimization: if device 0 function 0 on a bus returns vendor ID 0xFFFF, skip the remaining device slots on that bus
• Reduces PCI legacy scan from 32 buses × 32 devices = 1024 probes to ~63 probes on uhyve (which has a single device at bus 0 device 0)

Performance

Measured with RDTSC-based boot instrumentation on uhyve (3.7 GHz TSC):

• PCI legacy scan: 13,237 us → 797 us (16.6x faster)
• Total boot to application: ~17,900 us → ~5,500 us (3.3x faster)

Test plan

• Built and booted hello_world example via uhyve, device at 00:00 still discovered correctly

🤖 Generated with Claude Code

[github-actions]

Benchmark Results

Details

Benchmark	Current: 596d628	Previous: dd4adf7	Performance Ratio
startup_benchmark Build Time	99.42 s	100.04 s	0.99 ❗
startup_benchmark File Size	0.86 MB	0.86 MB	1.00 ❗
Startup Time - 1 core	0.87 s (±0.03 s)	0.97 s (±0.03 s)	0.90 ❗
Startup Time - 2 cores	0.90 s (±0.03 s)	0.97 s (±0.03 s)	0.93 ❗
Startup Time - 4 cores	0.89 s (±0.03 s)	0.96 s (±0.04 s)	0.93 ❗
multithreaded_benchmark Build Time	102.32 s	101.89 s	1.00 ❗
multithreaded_benchmark File Size	0.96 MB	0.96 MB	1.00 ❗
Multithreaded Pi Efficiency - 2 Threads	90.72 % (±9.15 %)	91.00 % (±9.06 %)	1.00
Multithreaded Pi Efficiency - 4 Threads	44.55 % (±4.15 %)	43.85 % (±3.35 %)	1.02
Multithreaded Pi Efficiency - 8 Threads	26.26 % (±2.46 %)	25.74 % (±2.15 %)	1.02
micro_benchmarks Build Time	111.89 s	113.74 s	0.98 ❗
micro_benchmarks File Size	0.96 MB	0.96 MB	1.00 ❗
Scheduling time - 1 thread	71.27 ticks (±3.18 ticks)	70.24 ticks (±3.59 ticks)	1.01
Scheduling time - 2 threads	39.86 ticks (±5.29 ticks)	39.12 ticks (±4.49 ticks)	1.02
Micro - Time for syscall (getpid)	2.97 ticks (±0.20 ticks)	2.99 ticks (±0.29 ticks)	0.99
Memcpy speed - (built_in) block size 4096	63635.92 MByte/s (±45158.67 MByte/s)	65087.76 MByte/s (±46625.38 MByte/s)	0.98
Memcpy speed - (built_in) block size 1048576	30045.91 MByte/s (±25007.78 MByte/s)	29936.81 MByte/s (±24889.06 MByte/s)	1.00
Memcpy speed - (built_in) block size 16777216	25077.57 MByte/s (±20994.58 MByte/s)	25527.51 MByte/s (±21459.57 MByte/s)	0.98
Memset speed - (built_in) block size 4096	64370.40 MByte/s (±45726.54 MByte/s)	65536.56 MByte/s (±46897.60 MByte/s)	0.98
Memset speed - (built_in) block size 1048576	30813.46 MByte/s (±25447.25 MByte/s)	30723.73 MByte/s (±25327.45 MByte/s)	1.00
Memset speed - (built_in) block size 16777216	25807.48 MByte/s (±21447.22 MByte/s)	26327.86 MByte/s (±21978.97 MByte/s)	0.98
Memcpy speed - (rust) block size 4096	57979.32 MByte/s (±42784.34 MByte/s)	57856.95 MByte/s (±42652.78 MByte/s)	1.00
Memcpy speed - (rust) block size 1048576	30065.26 MByte/s (±25142.63 MByte/s)	30116.15 MByte/s (±25100.80 MByte/s)	1.00
Memcpy speed - (rust) block size 16777216	24377.68 MByte/s (±20550.82 MByte/s)	24868.32 MByte/s (±20982.14 MByte/s)	0.98
Memset speed - (rust) block size 4096	58833.97 MByte/s (±43243.81 MByte/s)	58845.68 MByte/s (±43409.33 MByte/s)	1.00
Memset speed - (rust) block size 1048576	30866.86 MByte/s (±25573.40 MByte/s)	30915.72 MByte/s (±25554.06 MByte/s)	1.00
Memset speed - (rust) block size 16777216	25161.37 MByte/s (±21071.74 MByte/s)	25661.65 MByte/s (±21502.61 MByte/s)	0.98
alloc_benchmarks Build Time	103.92 s	106.25 s	0.98 ❗
alloc_benchmarks File Size	0.93 MB	0.93 MB	1.00 ❗
Allocations - Allocation success	100.00 %	100.00 %	1
Allocations - Deallocation success	100.00 %	100.00 %	1
Allocations - Pre-fail Allocations	100.00 %	100.00 %	1
Allocations - Average Allocation time	7698.02 Ticks (±309.70 Ticks)	13150.35 Ticks (±161.03 Ticks)	0.59 ❗
Allocations - Average Allocation time (no fail)	7698.02 Ticks (±309.70 Ticks)	13150.35 Ticks (±161.03 Ticks)	0.59 ❗
Allocations - Average Deallocation time	2230.97 Ticks (±605.34 Ticks)	1127.38 Ticks (±770.43 Ticks)	1.98 ❗
mutex_benchmark Build Time	104.88 s	104.47 s	1.00 ❗
mutex_benchmark File Size	0.96 MB	0.96 MB	1.00 ❗
Mutex Stress Test Average Time per Iteration - 1 Threads	13.10 ns (±0.67 ns)	13.02 ns (±0.58 ns)	1.01
Mutex Stress Test Average Time per Iteration - 2 Threads	15.84 ns (±0.78 ns)	15.66 ns (±0.86 ns)	1.01

This comment was automatically generated by workflow using github-action-benchmark.