Bug 198197

Summary:	Unexpected CFS throttling
Product:	Process Management	Reporter:	Ivan Babrou (ibobrik)
Component:	Scheduler	Assignee:	Ingo Molnar (mingo)
Status:	NEW ---
Severity:	high	CC:	chiluk
Priority:	P1
Hardware:	All
OS:	Linux
Kernel Version:	4.14.4	Subsystem:
Regression:	No	Bisected commit-id:

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.