volt-vmm/docs/benchmark-volt.md

Volt VMM Benchmark Results

Date: 2026-03-08 Version: Volt v0.1.0 Host: Intel Xeon Silver 4210R @ 2.40GHz (2 sockets × 10 cores, 40 threads) Host Kernel: Linux 6.1.0-42-amd64 (Debian) Methodology: 10 iterations per test, measuring wall-clock time from process start to kernel panic (no rootfs). Kernel: Linux 4.14.174 (vmlinux ELF format).

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Summary

Metric	Value
Binary size	3.10 MB (3,258,448 bytes)
Binary size (stripped)	3.10 MB (3,258,440 bytes)
Cold boot to kernel panic (median)	1,723 ms
VMM init time (median)	110 ms
VMM init time (min)	95 ms
Memory overhead (RSS - guest)	~6.6 MB
Startup breakdown (first log → VM running)	88.8 ms
Kernel boot time (internal)	~1.41 s
Dynamic dependencies	libc, libm, libgcc_s

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1. Binary Size

Metric	Size
Release binary	3,258,448 bytes (3.10 MB)
Stripped binary	3,258,440 bytes (3.10 MB)
Format	ELF 64-bit LSB PIE executable, dynamically linked

Dynamic dependencies:

• libc.so.6
• libm.so.6
• libgcc_s.so.1
• linux-vdso.so.1
• ld-linux-x86-64.so.2

Note: Binary is already stripped in release profile (only 8 bytes difference).

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2. Cold Boot Time (Process Start → Kernel Panic)

Full end-to-end time from process launch to kernel panic detection. This includes VMM initialization, kernel loading, and the Linux kernel's full boot sequence (which ends with a panic because no rootfs is provided).

vmlinux-4.14 (128M RAM)

Iteration	Time (ms)
1	1,750
2	1,732
3	1,699
4	1,704
5	1,730
6	1,736
7	1,717
8	1,714
9	1,747
10	1,703

Stat	Value
Minimum	1,699 ms
Maximum	1,750 ms
Median	1,723 ms
Average	1,723 ms
Spread	51 ms (2.9%)

vmlinux-firecracker-official (128M RAM)

Same kernel binary, different symlink path.

Iteration	Time (ms)
1	1,717
2	1,707
3	1,734
4	1,736
5	1,710
6	1,720
7	1,729
8	1,742
9	1,714
10	1,726

Stat	Value
Minimum	1,707 ms
Maximum	1,742 ms
Median	1,723 ms
Average	1,723 ms

Both kernel files are identical (21,441,304 bytes each). Results are consistent.

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3. VMM Init Time (Process Start → "VM is running")

This measures only the VMM's own initialization overhead, before any guest code executes. Includes KVM setup, memory allocation, CPUID configuration, kernel loading, vCPU creation, and register setup.

Iteration	Time (ms)
1	100
2	95
3	112
4	114
5	121
6	116
7	105
8	108
9	99
10	112

Stat	Value
Minimum	95 ms
Maximum	121 ms
Median	110 ms

Note: Measurement uses date +%s%N and polling for "VM is running" in output, which adds ~5-10ms of polling overhead. True VMM init time from TRACE logs is ~89ms.

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4. Startup Breakdown (TRACE-level Timing)

Detailed timing from TRACE-level logs, showing each VMM initialization phase:

Δ from start (ms)	Phase
+0.000	Program start (Volt VMM v0.1.0)
+0.124	KVM initialized (API v12, max 1024 vCPUs)
+0.138	Creating virtual machine
+29.945	CPUID configured (46 entries)
+72.049	Guest memory allocated (128 MB, anonymous mmap)
+72.234	VM created
+72.255	Loading kernel
+88.276	Kernel loaded (ELF vmlinux at 0x100000, entry 0x1000000)
+88.284	Serial console initialized (0x3f8)
+88.288	Creating vCPU
+88.717	vCPU 0 configured (64-bit long mode)
+88.804	Starting VM
+88.814	VM running
+88.926	vCPU 0 enters KVM_RUN

Phase Durations

Phase	Duration (ms)	% of Total
Program init → KVM init	0.1	0.1%
KVM init → CPUID config	29.8	33.5%
CPUID config → Memory alloc	42.1	47.4%
Memory alloc → VM create	0.2	0.2%
Kernel loading	16.0	18.0%
Device init + vCPU setup	0.6	0.7%
Total VMM init	88.9	100%

Key Observations

1. CPUID configuration takes ~30ms — calls KVM_GET_SUPPORTED_CPUID and filters 46 entries
2. Memory allocation takes ~42ms — mmap of 128MB anonymous memory + KVM_SET_USER_MEMORY_REGION
3. Kernel loading takes ~16ms — parsing 21MB ELF binary + page table setup
4. vCPU setup is fast — under 1ms including MSR configuration and register setup

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5. Memory Overhead

Measured RSS 2 seconds after VM start (guest kernel booted and running).

Guest Memory	RSS (kB)	VmSize (kB)	VmPeak (kB)	Overhead (kB)	Overhead (MB)
128 MB	137,848	2,909,504	2,909,504	6,776	6.6
256 MB	268,900	3,040,576	3,106,100	6,756	6.6
512 MB	535,000	3,302,720	3,368,244	10,712	10.5
1 GB	1,055,244	3,827,008	3,892,532	6,668	6.5

Overhead = RSS − Guest Memory Size

Stat	Value
Typical VMM overhead	~6.6 MB
Overhead components	Binary code/data, KVM structures, kernel image in-memory, page tables, serial buffer

Note: The 512MB case shows slightly higher overhead (10.5 MB). This may be due to kernel memory allocation patterns or measurement timing. The consistent ~6.6 MB for 128M/256M/1G suggests the true VMM overhead is approximately 6.6 MB.

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6. Kernel Internal Boot Time

Time from first kernel log message to kernel panic (measured from kernel's own timestamps in serial output):

Metric	Value
First kernel message	[0.000000] Linux version 4.14.174
Kernel panic	[1.413470] VFS: Unable to mount root fs
Kernel boot time	~1.41 seconds

This is the kernel's own view of boot time. The remaining ~0.3s of the 1.72s total is:

• VMM init: ~89ms
• Kernel rebooting after panic: ~1s (configured panic=1)
• Process teardown: small

Actual cold boot to usable kernel: ~89ms (VMM) + ~1.41s (kernel) ≈ 1.5s total.

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7. CPUID Configuration

Volt configures 46 CPUID entries for the guest vCPU.

Strategy

• Starts from KVM_GET_SUPPORTED_CPUID (host capabilities)
• Filters out features not suitable for guests:
  • Removed from leaf 0x1 ECX: DTES64, MONITOR/MWAIT, DS_CPL, VMX, SMX, EIST, TM2, PDCM
  • Added to leaf 0x1 ECX: HYPERVISOR bit (signals VM to guest)
  • Removed from leaf 0x1 EDX: MCE, MCA, ACPI thermal, HTT (single vCPU)
  • Removed from leaf 0x7 EBX: HLE, RTM (TSX), RDT_M, RDT_A, MPX
  • Removed from leaf 0x7 ECX: PKU, OSPKE, LA57
  • Cleared leaves: 0x6 (thermal), 0xA (perf monitoring)
  • Preserved: All SSE/AVX/AVX-512, AES, XSAVE, POPCNT, RDRAND, RDSEED, FSGSBASE, etc.

Key CPUID Values (from TRACE)

Leaf	Register	Value	Notes
0x0	EAX	22	Max standard leaf
0x0	EBX/EDX/ECX	GenuineIntel	Host vendor passthrough
0x1	ECX	0xf6fa3203	SSE3, SSSE3, SSE4.1/4.2, AVX, AES, XSAVE, POPCNT, HYPERVISOR
0x1	EDX	0x0f8bbb7f	FPU, TSC, MSR, PAE, CX8, APIC, SEP, PGE, CMOV, PAT, CLFLUSH, MMX, FXSR, SSE, SSE2
0x7	EBX	0xd19f27eb	FSGSBASE, BMI1, AVX2, SMEP, BMI2, ERMS, INVPCID, RDSEED, ADX, SMAP, CLFLUSHOPT, CLWB, AVX-512(F/DQ/CD/BW/VL)
0x7	EDX	0xac000400	SPEC_CTRL, STIBP, ARCH_CAP, SSBD
0x80000001	ECX	0x00000121	LAHF_LM, ABM, PREFETCHW
0x80000001	EDX	—	SYSCALL ✓, NX ✓, LM ✓, RDTSCP, 1GB pages
0x40000000	—	KVMKVMKVM	KVM hypervisor signature

Features Exposed to Guest

• Compute: SSE through SSE4.2, AVX, AVX2, AVX-512 (F/DQ/CD/BW/VL/VNNI), FMA, AES-NI, SHA
• Memory: SMEP, SMAP, CLFLUSHOPT, CLWB, INVPCID, PCID
• Security: IBRS, IBPB, STIBP, SSBD, ARCH_CAPABILITIES, NX
• Misc: RDRAND, RDSEED, XSAVE/XSAVEC/XSAVES, TSC (invariant), RDTSCP

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8. Test Environment

Component	Details
Host CPU	Intel Xeon Silver 4210R @ 2.40GHz (Cascade Lake)
Host RAM	Available (no contention during tests)
Host OS	Debian, Linux 6.1.0-42-amd64
KVM	API version 12, max 1024 vCPUs
Guest kernel	Linux 4.14.174 (vmlinux ELF, 21 MB)
Guest config	1 vCPU, variable RAM, no rootfs, console=ttyS0 reboot=k panic=1 pci=off
Volt	v0.1.0, release build, dynamically linked
Rust	nightly (cargo build --release)

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Notes

1. Boot time is dominated by the kernel (~1.41s kernel vs ~89ms VMM). VMM overhead is <6% of total boot time.
2. Memory overhead is minimal at ~6.6 MB regardless of guest memory size.
3. Binary is already stripped in release profile — strip saves only 8 bytes.
4. CPUID filtering is comprehensive — removes dangerous features (VMX, TSX, MPX) while preserving compute-heavy features (AVX-512, AES-NI).
5. Hugepages not tested — host has no hugepages allocated (HugePages_Total=0). The --hugepages flag is available but untestable.
6. Both kernels are identical — vmlinux-4.14 and vmlinux-firecracker-official.bin are the same file (same size, same boot times).