OOM and High CPU utilization in update_blocked_averages because of too many cfs_rqs in rq->leaf_cfs_rq_list

Bug #1747896 reported by Gavin Guo
This bug affects 2 people
Affects Status Importance Assigned to Milestone
linux (Ubuntu)
Gavin Guo

Bug Description

The CPU utilization keeps high and the flamegraph[1] shows that the CPU
is busy updating the load average in the for loop inside
update_blocked_averages() function. Also, the OOM happens because of
the decayed cfs_rqs are not released.

commit a9e7f6544b9cebdae54d29f87a7ba2a83c0471b5
Author: Tejun Heo <email address hidden>
Date: Tue Apr 25 17:43:50 2017 -0700

sched/fair: Fix O(nr_cgroups) in load balance path

Currently, rq->leaf_cfs_rq_list is a traversal ordered list of all
live cfs_rqs which have ever been active on the CPU; unfortunately,
this makes update_blocked_averages() O(# total cgroups) which isn't
scalable at all.

This shows up as a small CPU consumption and scheduling latency
increase in the load balancing path in systems with CPU controller
enabled across most cgroups. In an edge case where temporary cgroups
were leaking, this caused the kernel to consume good several tens of
percents of CPU cycles running update_blocked_averages(), each run
taking multiple millisecs.

This patch fixes the issue by taking empty and fully decayed cfs_rqs
off the rq->leaf_cfs_rq_list.

1). Running the script

for i in $(seq 1 10); do
        ( for j in $(seq 1 3000); do ssh -S none u@localhost date;done; echo "done $i" ) &

2). Observe the cfs_rqs
$ watch -n1 "grep cfs_rq /proc/sched_debug| wc -l"

3). Observe the CPU utilization rate
$ sudo htop

The patched kernel[2] shows that the CPU utilization rate is normal, the
cfs_rqs is decreased periodically, and the memory can be limited.

[1]. http://kernel.ubuntu.com/~gavinguo/168887/2018-01-31_07-38-45.perf.data.svg
[2]. https://launchpad.net/~mimi0213kimo/+archive/ubuntu/cfs-rq-clean

Revision history for this message
Gavin Guo (mimi0213kimo) wrote :
Revision history for this message
Ubuntu Kernel Bot (ubuntu-kernel-bot) wrote : Missing required logs.

This bug is missing log files that will aid in diagnosing the problem. While running an Ubuntu kernel (not a mainline or third-party kernel) please enter the following command in a terminal window:

apport-collect 1747896

and then change the status of the bug to 'Confirmed'.

If, due to the nature of the issue you have encountered, you are unable to run this command, please add a comment stating that fact and change the bug status to 'Confirmed'.

This change has been made by an automated script, maintained by the Ubuntu Kernel Team.

Changed in linux (Ubuntu):
status: New → Incomplete
Revision history for this message
Stefan Bader (smb) wrote :

The proposed patch was part of 4.13, so is included in Artful and later already. Thus setting to fix released for the main task.

Changed in linux (Ubuntu):
status: Incomplete → Fix Released
Changed in linux (Ubuntu Xenial):
assignee: nobody → Gavin Guo (mimi0213kimo)
importance: Undecided → Medium
status: New → In Progress
Changed in linux (Ubuntu):
assignee: Gavin Guo (mimi0213kimo) → nobody
Changed in linux (Ubuntu Xenial):
status: In Progress → Fix Committed
Revision history for this message
Stefan Bader (smb) wrote :

This bug is awaiting verification that the kernel in -proposed solves the problem. Please test the kernel and update this bug with the results. If the problem is solved, change the tag 'verification-needed-xenial' to 'verification-done-xenial'. If the problem still exists, change the tag 'verification-needed-xenial' to 'verification-failed-xenial'.

If verification is not done by 5 working days from today, this fix will be dropped from the source code, and this bug will be closed.

See https://wiki.ubuntu.com/Testing/EnableProposed for documentation how to enable and use -proposed. Thank you!

tags: added: verification-needed-xenial
Gavin Guo (mimi0213kimo)
tags: added: verification-done-xenial
removed: verification-needed-xenial
Revision history for this message
Launchpad Janitor (janitor) wrote :
Download full text (56.9 KiB)

This bug was fixed in the package linux - 4.4.0-119.143

linux (4.4.0-119.143) xenial; urgency=medium

  * linux: 4.4.0-119.143 -proposed tracker (LP: #1760327)

  * Dell XPS 13 9360 bluetooth scan can not detect any device (LP: #1759821)
    - Revert "Bluetooth: btusb: fix QCA Rome suspend/resume"

linux (4.4.0-118.142) xenial; urgency=medium

  * linux: 4.4.0-118.142 -proposed tracker (LP: #1759607)

  * Kernel panic with AWS 4.4.0-1053 / 4.4.0-1015 (Trusty) (LP: #1758869)
    - x86/microcode/AMD: Do not load when running on a hypervisor

  * CVE-2018-8043
    - net: phy: mdio-bcm-unimac: fix potential NULL dereference in

linux (4.4.0-117.141) xenial; urgency=medium

  * linux: 4.4.0-117.141 -proposed tracker (LP: #1755208)

  * Xenial update to 4.4.114 stable release (LP: #1754592)
    - x86/asm/32: Make sync_core() handle missing CPUID on all 32-bit kernels
    - usbip: prevent vhci_hcd driver from leaking a socket pointer address
    - usbip: Fix implicit fallthrough warning
    - usbip: Fix potential format overflow in userspace tools
    - x86/microcode/intel: Fix BDW late-loading revision check
    - x86/retpoline: Fill RSB on context switch for affected CPUs
    - sched/deadline: Use the revised wakeup rule for suspending constrained dl
    - can: af_can: can_rcv(): replace WARN_ONCE by pr_warn_once
    - can: af_can: canfd_rcv(): replace WARN_ONCE by pr_warn_once
    - PM / sleep: declare __tracedata symbols as char[] rather than char
    - time: Avoid undefined behaviour in ktime_add_safe()
    - timers: Plug locking race vs. timer migration
    - Prevent timer value 0 for MWAITX
    - drivers: base: cacheinfo: fix x86 with CONFIG_OF enabled
    - drivers: base: cacheinfo: fix boot error message when acpi is enabled
    - PCI: layerscape: Add "fsl,ls2085a-pcie" compatible ID
    - PCI: layerscape: Fix MSG TLP drop setting
    - mmc: sdhci-of-esdhc: add/remove some quirks according to vendor version
    - fs/select: add vmalloc fallback for select(2)
    - hwpoison, memcg: forcibly uncharge LRU pages
    - cma: fix calculation of aligned offset
    - mm, page_alloc: fix potential false positive in __zone_watermark_ok
    - ipc: msg, make msgrcv work with LONG_MIN
    - x86/ioapic: Fix incorrect pointers in ioapic_setup_resources()
    - ACPI / processor: Avoid reserving IO regions too early
    - ACPI / scan: Prefer devices without _HID/_CID for _ADR matching
    - ACPICA: Namespace: fix operand cache leak
    - netfilter: x_tables: speed up jump target validation
    - netfilter: arp_tables: fix invoking 32bit "iptable -P INPUT ACCEPT" failed
      in 64bit kernel
    - netfilter: nf_dup_ipv6: set again FLOWI_FLAG_KNOWN_NH at flowi6_flags
    - netfilter: nf_ct_expect: remove the redundant slash when policy name is
    - netfilter: nfnetlink_queue: reject verdict request from different portid
    - netfilter: restart search if moved to other chain
    - netfilter: nf_conntrack_sip: extend request line validation
    - netfilter: use fwmark_reflect in nf_send_reset
    - ext2: Don't clear SGID when inheriting ACLs
    - reiserfs: fix race in prealloc discard
    - re...

Changed in linux (Ubuntu Xenial):
status: Fix Committed → Fix Released
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