CPU usage increases after folder scans (and hence, over time) #9417
Description
- Syncthing: v1.27.3, Linux (64-bit Intel/AMD)
- OS: Debian 12, Kernel 6.1.0-18-amd64
- Size: 23.075 files, 1.738 dirs, ~45,6 GiB total size, 6 folders
- Staggered versioning enabled (not sure if relevant)
inotifywatches enabled
Observation
CPU usage is low in general (< 1 % on a small Intel SoC), but keeps growing slowly over time (after >2 days) to 2 % and above, i.e. by over a factor of two (in idle). After prolonged runtime of some weeks, I also observed > 4 %.
Reproduction steps
Either wait ;-), or run many folder rescans. Slowly hitting "Rescan all folders" about 80 times, then waiting until everything has settled down, CPU usage has increased, too.
So likely, the regular hourly scan is causing it.
Further information
Initially reported as:
https://forum.syncthing.net/t/slowly-increasing-cpu-usage-over-time/21639/2
(until I found a reproducer).
Note I also observe a higher rate of syscalls such as:
[pid 1605] epoll_pwait(4, [], 128, 0, NULL, 0) = 0
[pid 1605] epoll_pwait(4, [], 128, 0, NULL, 0) = 0
[pid 1605] epoll_pwait(4, <unfinished ...>
[pid 962] <... nanosleep resumed>NULL) = 0
[pid 962] futex(0x1a2afa0, FUTEX_WAIT_PRIVATE, 0, {tv_sec=0, tv_nsec=2996919}) = -1 ETIMEDOUT (Connection timed out)
[pid 1605] <... epoll_pwait resumed>[], 128, 13, NULL, 0) = 0
[pid 962] nanosleep({tv_sec=0, tv_nsec=10000000}, <unfinished ...>
[pid 1605] epoll_pwait(4, [], 128, 0, NULL, 0) = 0
[pid 1605] epoll_pwait(4, <unfinished ...>
[pid 962] <... nanosleep resumed>NULL) = 0
[pid 962] futex(0x1a2afa0, FUTEX_WAIT_PRIVATE, 0, {tv_sec=0, tv_nsec=1697811} <unfinished ...>
[pid 1605] <... epoll_pwait resumed>[], 128, 12, NULL, 0) = 0
[pid 962] <... futex resumed>) = -1 ETIMEDOUT (Connection timed out)
[pid 1605] epoll_pwait(4, <unfinished ...>
[pid 962] nanosleep({tv_sec=0, tv_nsec=10000000}, <unfinished ...>
[pid 1605] <... epoll_pwait resumed>[], 128, 0, NULL, 0) = 0
[pid 1605] epoll_pwait(4, [], 128, 0, NULL, 0) = 0
[pid 1605] epoll_pwait(4, <unfinished ...>
[pid 962] <... nanosleep resumed>NULL) = 0
[pid 962] futex(0x1a2afa0, FUTEX_WAIT_PRIVATE, 0, {tv_sec=0, tv_nsec=3958898} <unfinished ...>
[pid 1605] <... epoll_pwait resumed>[], 128, 14, NULL, 0) = 0
[pid 962] <... futex resumed>) = -1 ETIMEDOUT (Connection timed out)
in this state, but not sure whether this is really related.