stap trace blockdev’s iops

背景

群里的一个问题, 用dd来测试一个块设备的写性能, 因为可能会被os cache误导. 所以建议同时使用stap来跟踪一下.  
当然stap会带来一定的开销, 得到的实际结果会低于实际的IO水平.  
[root@db-172-16-3-150 io]# grep -r vfs.write.return /opt/systemtap/share/systemtap/tapset/*  
/opt/systemtap/share/systemtap/tapset/linux/vfs.stp:probe vfs.write.return = kernel.function("vfs_write").return  
  
probe vfs.write.return = kernel.function("vfs_write").return  
{  
        name = "vfs.write"  
        retstr = sprintf("%d", $return)  
  
        file = $file  
        pos = $pos  
        buf = $buf  
        bytes_to_write = $count  
        dev = __file_dev($file)  
        devname = __find_bdevname(dev, __file_bdev($file))  
        ino = __file_ino($file)  
  
        ret = $return  
        bytes_written = $return > 0 ? $return : 0  
        error = $return < 0 ? $return : 0  
        error_str = error ? errno_str(error) : ""  
}  
  
  
[root@db-172-16-3-150 io]# stap -L 'kernel.function("vfs_write")'  
kernel.function("vfs_write@fs/read_write.c:349") $file:struct file* $buf:char const* $count:size_t $pos:loff_t*  
  
使用如下脚本 :   
stap -e 'global total_time, total_bytes, total_reqs  
  
probe vfs.write.return {  
  ts = gettimeofday_ns() - @entry(gettimeofday_ns())  
  if ($return>0) {  
    if (devname!="N/A") { /*skip update cache*/  
      total_time[devname] += ts  
      total_bytes[devname] += $return  
      total_reqs[devname] += 1  
    }  
  }  
}  
  
probe timer.s(3) {  
  foreach(dev in total_time) {  
    printf("dev:%s  Wreqs/s:%d  WKbytes/s:%d\n", dev, total_reqs[dev]/3, (1000000000*total_bytes[dev])/(total_time[dev]*1024))  
  }  
  delete total_time  
  delete total_bytes  
  delete total_reqs  
}'  
输出举例:  
dev:sdb1  Wreqs/s:108606  WKbytes/s:152986  
dev:sdb1  Wreqs/s:108150  WKbytes/s:152320  
dev:sdb1  Wreqs/s:108173  WKbytes/s:152246  
dd 一个文件, 输出 :   
[root@db-172-16-3-150 ssd4]# dd if=/dev/zero of=./test.img bs=1k count=10240000  
10240000+0 records in  
10240000+0 records out  
10485760000 bytes (10 GB) copied, 96.6477 s, 108 MB/s  

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