Hey!
May I ask, what would be the practical usage of 500x 1MB buffers? What kind
of problem are you solving?
Best,
-W
niedziela, 5 marca 2023 o 22:13:57 UTC+1 Kursk napisał(a):
> Oh, interesting enough this performance degradation shows only in some
> Linux boxes (heavily optimised) from a LAB... I guess then this behaviour
> might be related to the specific Linux OS settings that those boxes have.
>
> On Sunday 5 March 2023 at 20:36:08 UTC Kursk wrote:
>
>> Hi,
>> I've been recently experimenting with system pipes performance using Go,
>> trying to measure how fast I could read from STDIN to a buffer, then do
>> something with it.
>>
>> During that experiment I noticed a significant throughput degradation
>> when reading into the same buffer vs different (pre-allocated) buffers.
>>
>> To make things more interesting, this performance degradation seems to
>> happen on my Linux system only, when done in a Mac laptop throughput is
>> consistent regardless of the count of buffers I am writing to which is what
>> I was initially expecting.
>>
>> To remove throughput variance from cache misses, I've pinned both
>> processes to the same virtual core.
>>
>> My question is why is this happening? and, is there a way to avoid it?
>>
>> Below code snipped and command lines
>> ---------------------------------------
>>
>> $ taskset 0x1 cat 10GiB | taskset 0x1 ./stdin-to-buffer -buffer-count=*1*
>> Start time: 2023-03-05T12:26:21-08:00
>> Total bytes read: 10737418240
>> Chunks: 10240
>> *Throughput: 2903 MiB/s*
>> Total time: 3.527284627s
>> Finish time: 2023-03-05T12:26:25-08:00
>>
>> $ taskset 0x1 cat 10GiB | taskset 0x1 ./stdin-to-buffer -buffer-count=
>> *25*
>> Start time: 2023-03-05T12:26:29-08:00
>> Total bytes read: 10737418240
>> Chunks: 10240
>> *Throughput: 2531 MiB/s*
>> Total time: 4.045169972s
>> Finish time: 2023-03-05T12:26:34-08:00
>>
>> $ taskset 0x1 cat 10GiB | taskset 0x1 ./stdin-to-buffer -buffer-count=
>> *50*
>> Start time: 2023-03-05T12:26:39-08:00
>> Total bytes read: 10737418240
>> Chunks: 10240
>> *Throughput: 2215 MiB/s*
>> Total time: 4.623220632s
>> Finish time: 2023-03-05T12:26:43-08:00
>>
>> $ taskset 0x1 cat 10GiB | taskset 0x1 ./stdin-to-buffer -buffer-count=
>> *150*
>> Start time: 2023-03-05T12:26:49-08:00
>> Total bytes read: 10737418240
>> Chunks: 10240
>> *Throughput: 1916 MiB/s*
>> Total time: 5.344739086s
>> Finish time: 2023-03-05T12:26:54-08:00
>>
>> $ taskset 0x1 cat 10GiB | taskset 0x1 ./stdin-to-buffer -buffer-count=
>> *250*
>> Start time: 2023-03-05T12:26:59-08:00
>> Total bytes read: 10737418240
>> Chunks: 10240
>> *Throughput: 1732 MiB/s*
>> Total time: 5.910793462s
>> Finish time: 2023-03-05T12:27:05-08:00
>>
>> $ taskset 0x1 cat 10GiB | taskset 0x1 ./stdin-to-buffer -buffer-count=
>> *500*
>> Start time: 2023-03-05T12:27:13-08:00
>> Total bytes read: 10737418240
>> Chunks: 10240
>> *Throughput: 1757 MiB/s*
>> Total time: 5.827294797s
>> Finish time: 2023-03-05T12:27:19-08:00
>>
>> ---------------------------------------
>> Code for stdin-to-buffer.go follows.
>> ---------------------------------------
>> package main
>>
>> import (
>> "bytes"
>> "flag"
>> "fmt"
>> "io"
>> "log"
>> "math"
>> "os"
>> "time"
>> )
>>
>> var (
>> bufCount = flag.Int("buffer-count", 8, "The number of buffers")
>> bufSize = flag.Int("buffer-size-bytes", 1048576 /*1MiB*/, "The
>> buffer size in bytes")
>> )
>>
>> func main() {
>> flag.Parse()
>>
>> var nBytes, nChunks int
>>
>> bufPool := make([][]byte, *bufCount)
>> for i := 0; i < *bufCount; i++ {
>> bufPool[i] = make([]byte, *bufSize)
>> }
>>
>> var startTime = time.Now()
>> var loopIteration = -1
>>
>> loop:
>> for {
>> loopIteration++
>> buf := bufPool[loopIteration%*bufCount]
>> n, err := io.ReadFull(os.Stdin, buf)
>>
>> if n > 0 {
>> nChunks++
>> nBytes += n
>> }
>>
>> switch err {
>> case nil:
>> continue
>> case io.EOF, io.ErrUnexpectedEOF:
>> break loop
>> }
>> log.Fatal(err)
>> }
>>
>> finishTime := time.Now()
>> totalTime := finishTime.Sub(startTime)
>> fmt.Fprintf(os.Stderr, "Start time: %v\n", startTime.Format(time.
>> RFC3339))
>> fmt.Fprintf(os.Stderr, "Total bytes read: %v\n", nBytes)
>> fmt.Fprintf(os.Stderr, "Chunks: %v\n", nChunks)
>> fmt.Fprintf(os.Stderr, "Throughput: %v MiB/s\n", math.Round(
>> float64(nBytes)/math.Pow(1024, 2)/totalTime.Seconds()))
>> fmt.Fprintf(os.Stderr, "Total time: %v\n", totalTime)
>> fmt.Fprintf(os.Stderr, "Finish time: %v\n", finishTime.Format(
>> time.RFC3339))
>> }
>>
>
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