如何在Go中快速计算线条？

Question

这是代码

package main
import (
    "fmt"
    "os"
    "bufio"
)
func main() {
    fi, err := os.Open("/tmp/messages")
    if err != nil {
        panic(err)
    }
    defer func() {
        if err := fi.Close(); err != nil {
            panic(err)
        }
    }()
    scanner := bufio.NewScanner(fi)
    lines := 0
    for scanner.Scan() {
        scanner.Bytes()
        lines += 1
    }
    fmt.Println(lines)
    if err := scanner.Err(); err != nil {
        panic(err)
    }
}

这是经过的时间

5675143

real    0m0.548s
user    0m0.437s
sys     0m0.119s

＆＃34; wc＆＃34;花费了两倍的时间。对于588Mb的日志文件

wc -l / tmp / messages

5675142 /tmp/messages

real    0m0.231s
user    0m0.150s
sys     0m0.081s

pprof的结果是

540ms of 540ms total (  100%)
      flat  flat%   sum%        cum   cum%
     200ms 37.04% 37.04%      200ms 37.04%  syscall.Syscall
     190ms 35.19% 72.22%      190ms 35.19%  runtime.indexbytebody
     100ms 18.52% 90.74%      520ms 96.30%  bufio.(*Scanner).Scan
      20ms  3.70% 94.44%      210ms 38.89%  bufio.ScanLines
      10ms  1.85% 96.30%      530ms 98.15%  main.main
      10ms  1.85% 98.15%      210ms 38.89%  os.(*File).Read
      10ms  1.85%   100%       10ms  1.85%  runtime.usleep
         0     0%   100%      200ms 37.04%  os.(*File).read
         0     0%   100%      530ms 98.15%  runtime.goexit
         0     0%   100%      530ms 98.15%  runtime.main
         0     0%   100%       10ms  1.85%  runtime.mstart
         0     0%   100%       10ms  1.85%  runtime.mstart1
         0     0%   100%       10ms  1.85%  runtime.sysmon
         0     0%   100%      200ms 37.04%  syscall.Read
         0     0%   100%      200ms 37.04%  syscall.read

有没有办法优化代码以更快地运行？我的猜测是调用系统调用对总时间贡献100毫秒的开销。大部分时间可能花在Scanner内部的数据复制上。