1 2 Previous Next 15 Replies Latest reply on Apr 10, 2015 2:37 PM by aleki_intel

    High write latency on Intel Pro 1500 SSD

    stef3a

      Hello!

       

      I recently upgraded my laptop with a brand new Intel Pro 1500 SSD (180 GB). While trying out various measurements using Linux tools - I'm a performance addict - I discovered something interesting.


      I've recorded some IO operations (mostly write sync) with latency of about 170 ms ! I couldn't believe it: an SSD 1 OOM slower than an HDD?

       

      Workload: normal working sessions, no stress at all. OS is Ubuntu 14.04 (trim enabled by default via a crontab weekly job), application running were Chromium browser and a Win 7 KVM VM with MS office open. Filling status:

       

      $ df -h

      Filesystem      Size  Used Avail Use% Mounted on

      /dev/sda5      101G  71G  25G  74% /

      none            4,0K    0  4,0K  0% /sys/fs/cgroup

      udev            3,8G  4,0K  3,8G  1% /dev

      tmpfs          768M  1,3M  767M  1% /run

      none            5,0M    0  5,0M  0% /run/lock

      none            3,8G  38M  3,8G  1% /run/shm

      none            100M  68K  100M  1% /run/user

      /dev/sda2        57G  33G  24G  58% /media/ste/Windows7_OS

       

      Here is an example of the latency data, which I recorded and confirmed with multiple tools: Brendan Gregg ftrace scripts (brendangregg/perf-tools · GitHub), blktrace/blkparse/btt, iostat -x 1.

       

      Example:

      sudo ./iolatency:

      >=(ms) .. <(ms)  : I/O      |Distribution                          |

       

            0 -> 1      : 0        |                                      |

            1 -> 2      : 0        |                                      |

            2 -> 4      : 0        |                                      |

            4 -> 8      : 1        |##                                    |

            8 -> 16      : 1        |##                                    |

            16 -> 32      : 0        |                                      |

            32 -> 64      : 0        |                                      |

            64 -> 128    : 0        |                                      |

          128 -> 256    : 32      |######################################|

      sudo ./iosnoop:

       

      Tracing block I/O. Ctrl-C to end.

      COMM            PID    TYPE DEV      BLOCK        BYTES    LATms

      jbd2/sda5-166    166    WS  8,0      227094344    53248    177.84

      <idle>          0      WS  8,0      227094448    4096      2.02

      kworker/u16:0    20402  W    8,0      178377528    4096    175.48

      kworker/u16:0    20402  W    8,0      178377472    4096    175.46

      kworker/u16:0    20402  W    8,0      230578432    4096    175.46

      kworker/u16:0    20402  W    8,0      178377696    4096    175.50

      kworker/u16:0    20402  W    8,0      230431976    4096    176.35

      kworker/u16:0    20402  W    8,0      230409184    4096    176.36

      kworker/u16:0    20402  W    8,0      121944064    4096    178.21

      kworker/u16:0    20402  WM  8,0      121944088    4096    178.24

      kworker/u16:0    20402  WM  8,0      121944112    4096    178.24

      kworker/u16:0    20402  WM  8,0      159693064    4096    178.79

      kworker/u16:0    20402  WM  8,0      205830272    4096    178.81

      kworker/u16:0    20402  WM  8,0      226801776    4096    179.03

      kworker/u16:0    20402  WM  8,0      285522744    4096    179.04

      kworker/u16:0    20402  WM  8,0      289716352    4096    179.30

      kworker/u16:0    20402  WM  8,0      289716480    4096    179.32

      kworker/u16:0    20402  WM  8,0      289717120    4096    179.56

      kworker/u16:0    20402  WM  8,0      289782040    4096    179.58

      kworker/u16:0    20402  WM  8,0      302301320    4096    179.59

      kworker/u16:0    20402  WM  8,0      306493488    4096    179.59

       

       

      I have tried the same measurements on a older and cheaper SSD (with the same OS and applications) and did not see such latency peaks.

       

       

      Am I missing something? What could be the cause of this?

       

       

      Thank you!

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