[erlang-questions] child_setup high CPU usage

Rick Reed rr@REDACTED
Fri Jun 14 03:35:34 CEST 2013

We use this patch: https://github.com/reedr/otp/commit/b3420b3632c94d4c4869e88f057ca659aa513aea
to use closefrom(3) (which is supported on FreeBSD).


On 6/13/13 1:04 PM, Ransom Richardson wrote:
> To answer at least part of my own question, I think the issue was cause by increasing the ulimit for nofile to 1000000. Here's the child_setup line:
> /usr/local/lib/erlang/erts-5.10.1/bin/child_setup false . exec /bin/sh -s unix:cmd 2>&1 3:999999 50:1 56:0 -
> ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
> *From:* erlang-questions-bounces@REDACTED on behalf of Ransom Richardson
> *Sent:* Thursday, June 13, 2013 3:36 PM
> *To:* erlang-questions@REDACTED
> *Subject:* [erlang-questions] child_setup high CPU usage
> I'm seeing an issue where under what should be light load I see two child_setup processes spawned by Erlang using 100% CPU (combined) and making my machine unresponsive for a number of seconds.
> I recently updated to R16B and never saw this issue on previous releases.
> This happens when processing files sent over ssl from a client. My code uploads the files to S3 (using erlcloud, which uses httpc). If the client uploads only a few files it works fine. But if the client uploads about 6 files in a row then I see the behavior where the two child_setup processes consume 100% CPU. I would expect the only CPU intensive parts of this operation to be the calls to digest and MAC the S3 request. I'm not aware of any calls made to the shell in this scenario.
> I plan to debug further, but would be interested if anyone else has seen this or has ideas as to what could be causing this or how best to start looking.
> thanks,
> Ransom
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