Bug 198197 - Unexpected CFS throttling
Summary: Unexpected CFS throttling
Status: NEW
Alias: None
Product: Process Management
Classification: Unclassified
Component: Scheduler (show other bugs)
Hardware: All Linux
: P1 high
Assignee: Ingo Molnar
URL:
Keywords:
Depends on:
Blocks:
 
Reported: 2017-12-18 23:03 UTC by Ivan Babrou
Modified: 2019-11-08 22:10 UTC (History)
1 user (show)

See Also:
Kernel Version: 4.14.4
Tree: Mainline
Regression: No


Attachments

Description Ivan Babrou 2017-12-18 23:03:52 UTC
Originally reported here: http://lkml.iu.edu/hypermail/linux/kernel/1712.0/07072.html

We're seeing unexpected CFS throttling. I wrote down detailed
description with an easily reproducible case here:

* https://gist.github.com/bobrik/2030ff040fad360327a5fab7a09c4ff1

TL;DR is that even though we don't burn through CFS quota during the
period, throttling kicks in anyways. The larger interval between wakes
up is, the higher chance of throttling we get. We're seeing this on
different kernels (4.4, 4.9, 4.14) and different distros (different
kernel configs).

In corner cases well behaved applications that stay within quota get
delayed for two periods in a row, which means 200ms latency with
systemd.
Comment 1 Dave 2019-05-24 21:39:41 UTC
This issue has been resolved by 512ac999.  However 512ac999 caused another separate regression that I've submitted patches for.

https://lkml.org/lkml/2019/5/17/581
Comment 2 Dave 2019-11-08 22:10:16 UTC
My fixes have been accepted as commit de53fd7aed, and a clean-up fix of 763a9ec06c4.  

This should be closed as resolved.

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