计算机组成 -- IO_WAIT

IO性能

  1. 硬盘厂商的性能报告:响应时间(Response Time)、数据传输率(Data Transfer Rate)
  2. HDD硬盘一般用的是SATA 3.0的接口;SSD硬盘通常会用两种接口,一部分用SATA 3.0接口,另一部分用PCI Express接口
  3. 数据传输率
    • SATA 3.0接口的带宽是6Gb/s ≈ 768MB/s
      • 日常用的HDD硬盘的数据传输率,一般在200MB/s
      • SATA 3.0接口的SSD的数据传输率差不多是500MB/s
    • PCI Express接口的SSD,读取时的数据传输率能到2GB/s,写入时的数据传输率也能有1.2GB/s,大致是HDD的10倍
  4. 响应时间
    • 程序发起一个硬盘的读取或写入请求,直到请求返回的时间
    • SSD的响应时间大致在几十微秒这个级别,HDD的响应时间大致在十几毫秒这个级别,相差几十倍几百倍
  5. IOPS
    • 每秒读写的次数,相对于响应时间,更关注IOPS这个性能指标
    • 顺序读写和随机读写的情况下,硬盘的性能是完全不同的
  6. IOPSDTR才是IO性能的核心指标
    • 在实际的应用开发当中,对于数据的访问,更多的是随机读写,而不是顺序读写
    • 因此随机读写的IOPS才是IO性能的核心指标

定位IO_WAIT

  1. IOPS:HDD100SSD20,000
  2. CPU的主频通常在2GHz以上,即每秒可以做20亿次操作 – 性能瓶颈在IO上

top

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top - 12:45:53 up 455 days, 23:33,  0 users,  load average: 7.64, 7.20, 6.37
Tasks: 5 total, 1 running, 4 sleeping, 0 stopped, 0 zombie
Cpu(s): 9.4%us, 4.3%sy, 0.0%ni, 85.5%id, 0.1%wa, 0.0%hi, 0.7%si, 0.0%st
Mem: 131889644k total, 125159508k used, 6730136k free, 510392k buffers
Swap: 0k total, 0k used, 0k free, 21547136k cached

PID USER PR NI VIRT RES SHR S %CPU %MEM TIME+ COMMAND
19 dc 20 0 25.2g 8.7g 9.8m S 55.6 6.9 2258:13 java
1 dc 20 0 108m 3208 2520 S 0.0 0.0 0:00.04 bash
20 dc 20 0 121m 3840 2976 S 0.0 0.0 0:00.01 spk.log.rotate
110109 dc 20 0 108m 3676 2920 S 0.0 0.0 0:00.09 bash
110127 dc 20 0 17060 2028 1756 R 0.0 0.0 0:00.01 top

iostat

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avg-cpu:  %user   %nice %system %iowait  %steal   %idle
0.28 0.00 0.42 0.01 0.00 99.29

Device: tps kB_read/s kB_wrtn/s kB_read kB_wrtn
sda 0.61 12.89 7.65 197091 116954
sdb 0.01 0.17 0.00 2588 0
dm-0 0.56 12.09 7.51 184966 114886
dm-1 0.01 0.14 0.00 2204 0
  1. tps – IOPS
    • Indicate the number of transfers per second that were issued to the device.
    • A transfer is an I/O request to the device.
    • Multiple logical requests can be combined into a single I/O request to the device.
    • A transfer is of indeterminate size.
  2. kB_read/s – DTR
    • Indicate the amount of data read from the device expressed in a number of blocks (kilobytes, megabytes) per second.
    • Blocks are equivalent to sectors and therefore have a size of 512 bytes.
  3. kB_wrtn/s – DTR
    • Indicate the amount of data written to the device expressed in a number of blocks (kilobytes, megabytes) per second.

iotop

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Total DISK READ :	0.00 B/s | Total DISK WRITE :            0.00 B/s
Actual DISK READ: 0.00 B/s | Actual DISK WRITE: 0.00 B/s
TID PRIO USER DISK READ DISK WRITE SWAPIN IO> COMMAND
1 be/4 root 0.00 B/s 0.00 B/s 0.00 % 0.00 % systemd --switched-root --system --deserialize 22
2 be/4 root 0.00 B/s 0.00 B/s 0.00 % 0.00 % [kthreadd]
4 be/0 root 0.00 B/s 0.00 B/s 0.00 % 0.00 % [kworker/0:0H]
6 be/4 root 0.00 B/s 0.00 B/s 0.00 % 0.00 % [ksoftirqd/0]
7 rt/4 root 0.00 B/s 0.00 B/s 0.00 % 0.00 % [migration/0]

stress

通过stress命令,来模拟一个高IO负载的场景

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-d, --hdd N
spawn N workers spinning on write()/unlink()
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$ stress -d 2
stress: info: [1832] dispatching hogs: 0 cpu, 0 io, 0 vm, 2 hdd

top

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top - 01:54:07 up 7 min,  3 users,  load average: 1.23, 0.35, 0.14
Tasks: 110 total, 1 running, 109 sleeping, 0 stopped, 0 zombie
%Cpu(s): 0.0 us, 47.6 sy, 0.0 ni, 0.0 id, 47.3 wa, 0.0 hi, 5.1 si, 0.0 st
KiB Mem : 995748 total, 77876 free, 174772 used, 743100 buff/cache
KiB Swap: 2097148 total, 2097148 free, 0 used. 665188 avail Mem

PID USER PR NI VIRT RES SHR S %CPU %MEM TIME+ COMMAND
1834 root 20 0 8212 1124 32 D 17.9 0.1 0:06.67 stress
1833 root 20 0 8212 1124 32 D 16.6 0.1 0:06.58 stress

iostat

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avg-cpu:  %user   %nice %system %iowait  %steal   %idle
1.07 0.00 10.87 2.89 0.00 85.17

Device: tps kB_read/s kB_wrtn/s kB_read kB_wrtn
sda 179.72 265.56 86124.95 125565 40723320
sdb 0.19 5.47 0.00 2588 0
dm-0 177.67 239.89 86292.78 113431 40802680
dm-1 0.19 4.66 0.00 2204 0

iotop

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Total DISK READ :	0.00 0.00 BTotal DISK WRITE :          669.38 M/s
Actual DISK READ: 0.00 0.00 BActual DISK WRITE: 664.20 M/s
TID PRIO USER DISK READ DISK WRITE SWAPIN IO> COMMAND
1834 be/4 root 0.00 B/s 409.76 M/s 0.00 % 73.72 % stress -d 256:
1835 be/4 root 0.00 B/s 0.00 B/s 0.00 % 54.33 % [kworker/u256:0]
1833 be/4 root 0.00 B/s 218.48 M/s 0.00 % 53.71 % stress -d 256:
1 be/4 root 0.00 B/s 0.00 B/s 0.00 % 0.00 % systemd --switched-root --system --deserialize 22
2 be/4 root 0.00 B/s 0.00 B/s 0.00 % 0.00 % [kthreadd]
3 be/4 root 0.00 B/s 0.00 B/s 0.00 % 0.00 % [kworker/0:0]
0%