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manwe_
l33t
l33t


Joined: 01 Feb 2006
Posts: 615
Location: Kraków/Cracow, Poland

PostPosted: Mon Feb 12, 2018 9:08 pm    Post subject: ioping weirdness with nvme disk Reply with quote

Hi *.

Maybe you can explain this, I'm out of ideas:

First launch:
Code:
# ioping /dev/nvme0n1
4 KiB <<< /dev/nvme0n1 (block device 232.9 GiB): request=1 time=5.62 ms (warmup)
4 KiB <<< /dev/nvme0n1 (block device 232.9 GiB): request=2 time=5.72 ms
4 KiB <<< /dev/nvme0n1 (block device 232.9 GiB): request=3 time=5.59 ms
4 KiB <<< /dev/nvme0n1 (block device 232.9 GiB): request=4 time=5.61 ms
4 KiB <<< /dev/nvme0n1 (block device 232.9 GiB): request=5 time=5.75 ms
4 KiB <<< /dev/nvme0n1 (block device 232.9 GiB): request=6 time=5.57 ms
4 KiB <<< /dev/nvme0n1 (block device 232.9 GiB): request=7 time=5.77 ms (slow)
4 KiB <<< /dev/nvme0n1 (block device 232.9 GiB): request=8 time=5.66 ms
4 KiB <<< /dev/nvme0n1 (block device 232.9 GiB): request=9 time=5.58 ms (fast)
4 KiB <<< /dev/nvme0n1 (block device 232.9 GiB): request=10 time=5.73 ms
4 KiB <<< /dev/nvme0n1 (block device 232.9 GiB): request=11 time=5.70 ms
4 KiB <<< /dev/nvme0n1 (block device 232.9 GiB): request=12 time=5.63 ms
^C
--- /dev/nvme0n1 (block device 232.9 GiB) ioping statistics ---
11 requests completed in 62.3 ms, 44 KiB read, 176 iops, 706.2 KiB/s
generated 12 requests in 11.6 s, 48 KiB, 1 iops, 4.13 KiB/s
min/avg/max/mdev = 5.57 ms / 5.66 ms / 5.77 ms / 69.4 us


Second launch:
Code:
# ioping /dev/nvme0n1
4 KiB <<< /dev/nvme0n1 (block device 232.9 GiB): request=1 time=103.3 us (warmup)
4 KiB <<< /dev/nvme0n1 (block device 232.9 GiB): request=2 time=43.7 us
4 KiB <<< /dev/nvme0n1 (block device 232.9 GiB): request=3 time=92.7 us
4 KiB <<< /dev/nvme0n1 (block device 232.9 GiB): request=4 time=35.1 us
4 KiB <<< /dev/nvme0n1 (block device 232.9 GiB): request=5 time=29.3 us
4 KiB <<< /dev/nvme0n1 (block device 232.9 GiB): request=6 time=97.5 us
4 KiB <<< /dev/nvme0n1 (block device 232.9 GiB): request=7 time=91.4 us
4 KiB <<< /dev/nvme0n1 (block device 232.9 GiB): request=8 time=107.7 us (slow)
4 KiB <<< /dev/nvme0n1 (block device 232.9 GiB): request=9 time=93.7 us
4 KiB <<< /dev/nvme0n1 (block device 232.9 GiB): request=10 time=118.1 us (slow)
^C
--- /dev/nvme0n1 (block device 232.9 GiB) ioping statistics ---
9 requests completed in 709.2 us, 36 KiB read, 12.7 k iops, 49.6 MiB/s
generated 10 requests in 9.39 s, 40 KiB, 1 iops, 4.26 KiB/s
min/avg/max/mdev = 29.3 us / 78.8 us / 118.1 us / 31.4 us


Over 70 times slower with first launch (5.66 ms vs 78.8 us). What changed you ask? Duing second launch there was dd writing to the disk simultaneously with rate 100MBps.
Code:
pv -L 100M /dev/zero | dd of=zero bs=5M


How the hell ping is 70 times faster when disk is writing stuff then when it's idle?
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