100% disk usage without any process on I/O

[brauliobo]

Please see the screenshot:

Besides htop I/O tab, I'm also using iotop and fatrace -f r/fatrace -f w to try to find where the IO is coming from. Both show almost no relevant IO when idle, also because I'm using anything-sync-daemon to reduce IO in a couple of applications

Is there any other way to find the origin of this persistent 100% IO?

I'm using Archlinux, Seagate's 2tb SSD and BTRFS with zstd compression and snapshots

[natoscott]

What does the I/O tab show? I'm guessing nothing but still would be good to have a look. Its a very strange pattern where the Disk IO meter shows 100% use (from memory this is calculated using time-based fields from /proc/diskstats) but zero read/write bytes (those two are calculated from different fields based on IO's and bytes read/written) - indicates a very small number of small I/Os are taking a long time to complete (queued? slow device?).

Is CPU 11 showing ~100% I/O wait time or is that gray something else? It might be useful to add the PROCESSOR column (via F2/Setup) and see if that identifies a process running on that CPU? Bit of a long shot but you never know.

fatrace will only show application-level file I/O; you may have something happening at a lower level - try blktrace too.

[brauliobo]

Thanks for the detailed feedback @natoscott.

Below is a screenshot of the IO tab. The grey is indeed the color of IO. Also added the PROCESSOR column, there might be some overlap of IO in processor 11 and kwin_x11 CPU usage, but still uncertain.

A weird fact I've forgot to mention that this never happens when running htop with sudo, only with my personal user. Here it is a sample shot for sudo htop:

When using blktrace where the root and home partitions are I have the following output:

✗  sudo blktrace -d /dev/nvme0n1  
=== nvme0n1 ===
  CPU  0:                    0 events,        0 KiB data
  CPU  1:                   18 events,        1 KiB data
  CPU  2:                    0 events,        0 KiB data
  CPU  3:                    0 events,        0 KiB data
  CPU  4:                    0 events,        0 KiB data
  CPU  5:                    0 events,        0 KiB data
  CPU  6:                    0 events,        0 KiB data
  CPU  7:                  310 events,       15 KiB data
  CPU  8:                    1 events,        1 KiB data
  CPU  9:                    0 events,        0 KiB data
  CPU 10:                    0 events,        0 KiB data
  CPU 11:                    0 events,        0 KiB data
  Total:                   329 events (dropped 0),       16 KiB data

Although I also have a second NVMe, 3 USB HDDs, and 1 SATA HDD in the same machine. They are mostly inactive as they are there for backup and bigger files storage.

[natoscott]

Can you run the 'sudo htop' with the same htoprc file as your regular user? (there's no Disk IO meter shown currently)

And is that blktrace output from the same time htop is showing 100% I/O? (and how long was blktrace running there)

[brauliobo]

With the same htoprc now sudo htop also shows the same busy disk behavior. Here it is the htoprc config file.

Here it is a close to 1min new run of blktrace while having 100% disk usage in htop:

✗  sudo blktrace -d /dev/nvme0n1
=== nvme0n1 ===
  CPU  0:                    0 events,        0 KiB data
  CPU  1:                    0 events,        0 KiB data
  CPU  2:                    0 events,        0 KiB data
  CPU  3:                   70 events,        4 KiB data
  CPU  4:                  131 events,        7 KiB data
  CPU  5:                    0 events,        0 KiB data
  CPU  6:                    0 events,        0 KiB data
  CPU  7:                    0 events,        0 KiB data
  CPU  8:                    0 events,        0 KiB data
  CPU  9:                 1021 events,       48 KiB data
  CPU 10:                    0 events,        0 KiB data
  CPU 11:                    1 events,        1 KiB data
  Total:                  1223 events (dropped 0),       58 KiB

I've run in all other block devices and all of them only return 1 event.

[natoscott]

Interesting! There's two things that spring to mind then:

• it may be something the htop systemd meter is doing (talking to systemd) that is causing it (somehow, no idea how)
• I wonder if NFS maybe involved here? (nfsdcld there) ... is it possible there is NFS traffic happening? That may not be visible to blktrace. This is a bit of a stretch though, I'd be more inclined to suspect the first option.

Try switching off the htop systemd Meter next and see if the problem goes away.

[brauliobo]

I remember this issue for a long time, even before the systemd metric was there. I just removed to try but still no change.

NFS is indeed suspect. I stopped nfsd and nfsdcld without any change.
Another thing being used is sshfs. I've trying umounting 3 mount points on 2 other PCs to this machine and still no change.

Now I've finally found the option that disabling partially removes the issue, it is Detailed CPU time (System/IO-Wait/Hard-IRQ/Soft-IRQ/Steal/Guest). Disabling it remove the grey bar from the CPU, but still shows 100% Disk activity:

[natoscott]

I suspect that's just hiding the issue by not showing I/O wait anymore. See if 'iostat 1 10' shows any discard I/O? That's the only other thing I can think of that might explain it.

[brauliobo]

the 100% disk issue is gone for a while. I'll check iostat once it is back. thank you @natoscott for you kind support! I'll close the issue as it is definitely a question instead of an htop issue

[eworm-de]

I guess this is a duplicate of #1278... Did you install relevant kernel updates?

[natoscott]

@eworm-de difference here is the Disk IO Meter shows 100% use also (so both CPU metrics and diskstats showing IO time) - whereas in #1278 the Disk IO Meter shows 0%.

[brauliobo]

I guess this is a duplicate of #1278... Did you install relevant kernel updates?

I think so, here it is:

✗  uname -a
Linux bhavapower 6.4.12-arch1-1 #1 SMP PREEMPT_DYNAMIC Thu, 24 Aug 2023 00:38:14 +0000 x86_64 GNU/Linux