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!