Dotnet overhead of P/Invoke with ref arguments

1_MarshalBench.cs

using System.Runtime.InteropServices;
using BenchmarkDotNet.Attributes;
using BenchmarkDotNet.Jobs;

namespace net_array_bench_app.Benches
{

//    [SimpleJob(RuntimeMoniker.NetCoreApp31)]
//    [SimpleJob(RuntimeMoniker.Net60)]
    [SimpleJob(RuntimeMoniker.Net70)]
    [DisassemblyDiagnoser(maxDepth: 3)]
    public class MarshalBench
    {

        [Benchmark()]
        public unsafe void Fixed()
        {
            int x = 42;
            fixed(int* p = MemoryMarshal.CreateSpan(ref x,1))
            {
                test_ref(p);
            }
        }


        [Benchmark]
        public void RefParameter()
        {
            int x = 42;
            test_ref(ref x);
        }

        [SuppressGCTransition]
        [DllImport("libarray_bench_rs.so", EntryPoint = "test_ref")]
        unsafe static extern int test_ref(ref int  x);
        [SuppressGCTransition]
        [DllImport("libarray_bench_rs.so", EntryPoint = "test_ref")]
        unsafe static extern int test_ref(int*  x);      
    }
}

2_results.md

BenchmarkDotNet=v0.13.5, OS=manjaro 
AMD Ryzen 7 5800H with Radeon Graphics, 1 CPU, 16 logical and 8 physical cores
.NET SDK=7.0.103
  [Host]   : .NET 7.0.3 (7.0.323.12801), X64 RyuJIT AVX2
  .NET 7.0 : .NET 7.0.3 (7.0.323.12801), X64 RyuJIT AVX2

Job=.NET 7.0  Runtime=.NET 7.0  

Method	Mean	Error	StdDev	Code Size
Fixed	1.089 ns	0.0202 ns	0.0169 ns	65 B
RefParameter	2.940 ns	0.0180 ns	0.0150 ns	33 B

3_net_array_bench_app.Benches.MarshalBench-asm.md

.NET 7.0.3 (7.0.323.12801), X64 RyuJIT AVX2

; net_array_bench_app.Benches.MarshalBench.Fixed()
       push      rbp
       sub       rsp,10
       lea       rbp,[rsp+10]
       mov       dword ptr [rbp-4],2A
       lea       rdi,[rbp-4]
       mov       [rbp-10],rdi
       mov       rax,7F488E76C230
       call      rax
       xor       eax,eax
       mov       [rbp-10],rax
       cmp       dword ptr [7F488E6A4930],0
       jne       short M00_L01
M00_L00:
       add       rsp,10
       pop       rbp
       ret
M00_L01:
       call      CORINFO_HELP_POLL_GC
       jmp       short M00_L00
; Total bytes of code 65

.NET 7.0.3 (7.0.323.12801), X64 RyuJIT AVX2

; net_array_bench_app.Benches.MarshalBench.RefParameter()
       push      rbp
       sub       rsp,10
       lea       rbp,[rsp+10]
       mov       dword ptr [rbp-8],2A
       lea       rdi,[rbp-8]
       call      net_array_bench_app.Benches.MarshalBench.test_ref(Int32 ByRef)
       nop
       add       rsp,10
       pop       rbp
       ret
; Total bytes of code 33

PInvoke method net_array_bench_app.Benches.MarshalBench.test_ref(Int32 ByRef)

4_native.rs

#[no_mangle]
pub extern "C" fn test_ref(x:*mut i32){}