ring_test.go

Documentation: github.com/cilium/ebpf/perf

     1  package perf
     2  
     3  import (
     4  	"bytes"
     5  	"io"
     6  	"os"
     7  	"testing"
     8  
     9  	"github.com/cilium/ebpf/internal/unix"
    10  )
    11  
    12  func TestRingBufferReader(t *testing.T) {
    13  	buf := make([]byte, 2)
    14  
    15  	ring := makeRing(2, 0)
    16  	n, err := ring.Read(buf)
    17  	if err != io.EOF {
    18  		t.Error("Expected io.EOF, got", err)
    19  	}
    20  	if n != 2 {
    21  		t.Errorf("Expected to read 2 bytes, got %d", n)
    22  	}
    23  	if !bytes.Equal(buf, []byte{0, 1}) {
    24  		t.Error("Expected [0, 1], got", buf)
    25  	}
    26  	n, err = ring.Read(buf)
    27  	if err != io.EOF {
    28  		t.Error("Expected io.EOF, got", err)
    29  	}
    30  	if n != 0 {
    31  		t.Error("Expected to read 0 bytes, got", n)
    32  	}
    33  
    34  	// Wrapping read
    35  	ring = makeRing(2, 1)
    36  	n, err = io.ReadFull(ring, buf)
    37  	if err != nil {
    38  		t.Error("Error while reading:", err)
    39  	}
    40  	if n != 2 {
    41  		t.Errorf("Expected to read 2 byte, got %d", n)
    42  	}
    43  	if !bytes.Equal(buf, []byte{1, 0}) {
    44  		t.Error("Expected [1, 0], got", buf)
    45  	}
    46  }
    47  
    48  func makeRing(size, offset int) *ringReader {
    49  	if size != 0 && (size&(size-1)) != 0 {
    50  		panic("size must be power of two")
    51  	}
    52  
    53  	ring := make([]byte, size)
    54  	for i := range ring {
    55  		ring[i] = byte(i)
    56  	}
    57  
    58  	meta := unix.PerfEventMmapPage{
    59  		Data_head: uint64(len(ring) + offset),
    60  		Data_tail: uint64(offset),
    61  		Data_size: uint64(len(ring)),
    62  	}
    63  
    64  	return newRingReader(&meta, ring)
    65  }
    66  
    67  func TestPerfEventRing(t *testing.T) {
    68  	check := func(buffer, watermark int) {
    69  		ring, err := newPerfEventRing(0, buffer, watermark)
    70  		if err != nil {
    71  			t.Fatal(err)
    72  		}
    73  
    74  		size := len(ring.ringReader.ring)
    75  
    76  		// Ring size should be at least as big as buffer
    77  		if size < buffer {
    78  			t.Fatalf("ring size %d smaller than buffer %d", size, buffer)
    79  		}
    80  
    81  		// Ring size should be of the form 2^n pages (meta page has already been removed)
    82  		if size%os.Getpagesize() != 0 {
    83  			t.Fatalf("ring size %d not whole number of pages (pageSize %d)", size, os.Getpagesize())
    84  		}
    85  		nPages := size / os.Getpagesize()
    86  		if nPages&(nPages-1) != 0 {
    87  			t.Fatalf("ring size %d (%d pages) not a power of two pages (pageSize %d)", size, nPages, os.Getpagesize())
    88  		}
    89  	}
    90  
    91  	// watermark > buffer
    92  	_, err := newPerfEventRing(0, 8192, 8193)
    93  	if err == nil {
    94  		t.Fatal("watermark > buffer allowed")
    95  	}
    96  
    97  	// watermark == buffer
    98  	_, err = newPerfEventRing(0, 8192, 8192)
    99  	if err == nil {
   100  		t.Fatal("watermark == buffer allowed")
   101  	}
   102  
   103  	// buffer not a power of two, watermark < buffer
   104  	check(8193, 8192)
   105  
   106  	// large buffer not a multiple of page size at all (prime)
   107  	check(65537, 8192)
   108  }
   109
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