Hi. This is still not correct. Use the “for.. in b.N” as discussed in the blog
in order to understand the per op difference - which will be more accurate for
a microbenchmark timing,
But, if you really want to make a case that bit mask is slower than mod, then a
simpler test would be better - you can do these ops on in loop using b.N to
time the difference.
> On May 12, 2024, at 8:28 PM, Yuta MIYAKE <yuta_miy...@mercari.com> wrote:
>
> Thank you.
>
> This is benchstat result. new test code follows:
>
> ❯ go test -test.bench BenchmarkTestSingleModulo -count=10 -cpu=1 > modulo.txt
> ❯ go test -test.bench BenchmarkTestSingleBitMask -count=10 -cpu=1 >
> bitmask.txt
> ❯ benchstat modulo.txt bitmask.txt
> goos: darwin
> goarch: arm64
> pkg: ringbuffer
> │ modulo.txt │ bitmask.txt │
> │ sec/op │ sec/op vs base │
> TestSingleModulo 6.648 ± 1%
> TestSingleBitMask 6.694 ± 5%
> geomean 6.648 6.694 ? ¹ ²
>
>
> new test code:
>
> const BufferSize = 2 * 1024 * 1024
>
> func benchmarkSingle(rb RingBuffer) {
> total := 500000
> for i := 0; i < total; i++ {
> for j := 0; j < 1000; j++ {
> rb.Enqueue(j)
> }
> for j := 0; j < 1000; j++ {
> rb.Dequeue()
> }
> }
> }
>
> func BenchmarkTestSingleModulo(b *testing.B) {
> rb := NewRingBuffer0(BufferSize)
> b.ResetTimer()
> benchmarkSingle(rb)
> }
>
> func BenchmarkTestSingleBitMask(b *testing.B) {
> rb := NewRingBuffer1(BufferSize)
> b.ResetTimer()
> benchmarkSingle(rb)
> }
>
> On Monday, May 13, 2024 at 8:20:05 AM UTC+9 robert engels wrote:
> Use the Go benchmarking facilities, see
> https://dave.cheney.net/2013/06/30/how-to-write-benchmarks-in-go
> <https://dave.cheney.net/2013/06/30/how-to-write-benchmarks-in-go>
>
>
>> On May 11, 2024, at 9:57 PM, leon <leonca...@gmail.com
>> <applewebdata://6580EDE1-4ABA-43A4-BCDE-DB83F7616ADE>> wrote:
>>
>
>> I'm trying to prove an optimization technique for ring buffer is effective.
>> One of the technique is using bitmask instead of modulo to calculate a wrap
>> around. However, in my environment, modulo is slightly faster in a test
>> where 1 billion items are enqueued /dequeued by a single goroutine. What do
>> you think could be the cause?
>>
>> Full code:
>> https://go.dev/play/p/H933oqrhPI- <https://go.dev/play/p/H933oqrhPI->
>>
>> Environment:
>> * go version go1.21.4 darwin/arm64
>> * Apple M1 Pro
>>
>> RingBuffer with modulo:
>> ```
>> type RingBuffer0 struct {
>> writeIdx uint64
>> readIdx uint64
>> buffers []any
>> size uint64
>> }
>>
>> func NewRingBuffer0(size uint64) *RingBuffer0 {
>> rb := &RingBuffer0{}
>> rb.init(size)
>> return rb
>> }
>>
>> func (rb *RingBuffer0) init(size uint64) {
>> rb.buffers = make([]any, size)
>> rb.size = size
>> }
>>
>> func (rb *RingBuffer0) Enqueue(item any) error {
>> if rb.writeIdx-rb.readIdx == rb.size {
>> return ErrBufferFull
>> }
>> rb.buffers[rb.writeIdx%rb.size] = item
>> rb.writeIdx++
>> return nil
>> }
>>
>> func (rb *RingBuffer0) Dequeue() (any, error) {
>> if rb.writeIdx == rb.readIdx {
>> return nil, ErrBufferEmpty
>> }
>> item := rb.buffers[rb.readIdx%rb.size]
>> rb.readIdx++
>> return item, nil
>> }
>> ```
>>
>> RingBuffer with bitmask:
>> change each module calculation to the code below
>> * rb.buffers[rb.writeIdx&(rb.size-1)] = item
>> * item := rb.buffers[rb.readIdx&(rb.size-1)]
>>
>> Test:
>> func TestSingle(rb RingBuffer) {
>> start := time.Now()
>> total := 500000
>> for i := 0; i < total; i++ {
>> for j := 0; j < 1000; j++ {
>> rb.Enqueue(j)
>> }
>> for j := 0; j < 1000; j++ {
>> rb.Dequeue()
>> }
>> }
>> end := time.Now()
>> count := total * 2000
>> duration := end.Sub(start).Milliseconds()
>> fmt.Printf("%d ops in %d ms\n", count, duration)
>> }
>>
>>
>
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