100% CPU just transferring files?


I have an underpowered CPU (Intel Pentium processor D1508) but I still wouldn’t expect Syncthing to saturate the CPU while transferring files (it is not scanning).

I took some cpu profiles: would anyone have the time to take a peek and tell me what might be the issue here?

syncthing-cpu-linux-amd64-v1.23.2-122555.pprof (16.4 KB)

syncthing-cpu-linux-amd64-v1.23.2-122513.pprof (17.5 KB)

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Well, something is going to be the limit – if it’s not the network or the I/O it’s going to be the CPU. If that CPU doesn’t offer whatever extensions are used for hardware crypto & hashing then that’s likely to be the bottleneck. :person_shrugging:

Profile boils down to … crypto, and hashing:


Thank you for taking a look. This is a 2-core 4-thread CPU with support for AES-NI. I have no idea what else to check wrt crypto/hasing support but here is the Intel Ark page: Intel Pentium Processor D1508 3M Cache 2.20 GHz Product Specifications

Also, I should note that it’s not just using 100% CPU but also bottlenecked to 30MB/s transfer speeds (this is a 10gbe pipe)

AES-NI is not very useful for SHA256.

2 core 4 threads is less than what most people carry in their pockets nowadays, and phones, while still being considered “weak” devices, usually ship SHA extensions on newer CPUs.

I suspect the transfer rate will be simillar to the hashing rate reported on startup.


I didn’t realize htop hid kernel processes by default. It looks like I am hitting a performance bottleneck with my CPU but it’s not coming from Syncthing’s hashing: it’s my zfs pools encryption. This CPU is so freaking old it can’t handle writing to an encrypted filesystem. heh.

I guess an upgrade is in order.

Thanks @AudriusButkevicius and @calmh!


…this support request thread should be entered in the fame hall of support request threads…

  • providing all the necessary info in the first post
  • getting a diagram detailing what is happening by the devs
  • realizing the issue is something entirely different (albeit with no help from the forum)

Pure gold.

My compliments to both OP and the devs.


It’ll help keep you warm if you run it under your desk, though :slight_smile:

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Just a small addition, I run ST on a TrueNAS Core install running on an Intel G4560 build (2C/4T)/16GB ECC RAM. It works perfectly well and rarely uses 100% - I confess I don’t encrypt files though.

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