Confirmed mitigations=off gets things down to 18s in production
environment. I suppose there is still the outstanding question of why
the same python binary is 40% slower on ubuntu24 than ubuntu21, but at
least it isn't 6 times slower or worse.
** Changed in: linux (Ubuntu)
Status: New => Invalid
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https://bugs.launchpad.net/bugs/2083077
Title:
python3 counting 6x slowdown with ubuntu22 on cisco ucs hardware with
hyperthreading
Status in linux package in Ubuntu:
Invalid
Bug description:
I suspect this is a kernel bug.
With ubuntu <= 21, I find that this runs in about 13 seconds:
python3 -c "import timeit; print(timeit.Timer('for _ in range(0,1000):
pass').timeit())"
With ubuntu >= 22, I find that it runs in about 83 seconds.
The problem seems to be specific to Cisco UCS hardware and can be
mostly mitigated by disabling hyperthreading.
I also tried counting to a million a thousand times instead of
counting to 1000 a million times (this is how many times timeit runs
the experiment), just in case the time-measuring was the slow part,
but it made no difference. Even just a straight up loop without using
timeit shows about the same difference.
Originally, I encountered this when upgrading from 18 to 24. We went
back and isolated the problem to something that changed between 21 and
22. The version I actually care about is 24.
The only Cisco UCS systems we have are a bunch of Cisco UCS C220 M5SX
rack servers and a bunch of Cisco UCS B200 M5 blades. All of them
show the regression. I can confirm that on a variety of similarly-
specced supermicro systems, the regression does not occur.
The problem can be easily reproduced by booting off
https://releases.ubuntu.com/24.04.1/ubuntu-24.04.1-live-server-
amd64.iso (or various other versions) and dropping into a shell. The
installer kernel behaves the same as the installed kernel across the
various versions. So it should be possible for anyone with this
hardware to reproduce the issue by using the installer shells. You
may wish to use an old python3 from a version-pinned docker image to
get an apples-to-apples comparison.
If I run the experiment inside ubuntu18 containers on ubuntu21 and
ubuntu22 I can see that I still get the dramatically different
runtimes. i.e., the kernel version and not the userland or python
version is what seems to matter.
We have tried mitigations=off with no effect.
We have tried reverting various kernel scheduler configuration changes
back to their ubuntu21 settings with no effect.
We have tried disabling hyperthreading in the BIOS. This had an
enormous effect. It reduces runtime from 83 seconds to 17 seconds.
17 is still 30% slower than 13, but it is obviously way better than
83.
So just to recap:
13s: ubuntu21 with hyperthreading on
83s: ubuntu22 with hyperthreading on
17s: ubuntu22 with hyperthreading off
This machine has 2 sockets with 20 physical cores each for a total of
80 logical cores once we account for hyperthreading.
Ideally I would prefer not to be forced to disable hyperthreading.
Even if that is not possible, I am interested in avoiding the
remaining 30% slowdown.
sysbench --test=cpu and sysbench --test=memory also both exhibit a
slowdown, but it is more like a 30% slowdown instead of 800%, even
with hyperthreading turned on.
I have used perf to profile python and found the time was spread out--
did not see any particular smoking gun. The python process makes <
300 syscalls over its entire lifetime and virtually no context
switches. I tried running it with realtime priority with affinity for
a single core, which seemed to make little difference. The python
process uses 100% of a cpu as it runs.
Any ideas?
---
ProblemType: Bug
AlsaDevices:
total 0
crw-rw----+ 1 root audio 116, 1 Oct 2 19:29 seq
crw-rw----+ 1 root audio 116, 33 Oct 2 19:29 timer
AplayDevices: Error: [Errno 2] No such file or directory: 'aplay'
ApportVersion: 2.20.11-0ubuntu27.26
Architecture: amd64
ArecordDevices: Error: [Errno 2] No such file or directory: 'arecord'
AudioDevicesInUse: Error: command ['fuser', '-v', '/dev/snd/seq',
'/dev/snd/timer'] failed with exit code 1:
CasperMD5CheckResult: pass
DistroRelease: Ubuntu 20.04
InstallationDate: Installed on 2024-10-01 (0 days ago)
InstallationMedia: Ubuntu-Server 20.04.6 LTS "Focal Fossa" - Release amd64
(20230314.1)
IwConfig: Error: [Errno 2] No such file or directory: 'iwconfig'
Lsusb:
Bus 002 Device 001: ID 1d6b:0003 Linux Foundation 3.0 root hub
Bus 001 Device 003: ID 04b4:6570 Cypress Semiconductor Corp. Unprogrammed
CY7C65632/34 hub HX2VL
Bus 001 Device 004: ID 0624:0402 Avocent Corp. Cisco Virtual Keyboard and
Mouse
Bus 001 Device 002: ID 05a6:0a00 Cisco Systems, Inc. Integrated Management
Controller Hub
Bus 001 Device 001: ID 1d6b:0002 Linux Foundation 2.0 root hub
MachineType: Cisco Systems Inc UCSC-C220-M5SX
Package: linux (not installed)
PciMultimedia:
ProcEnviron:
TERM=linux
PATH=(custom, no user)
LANG=en_US.UTF-8
SHELL=/bin/bash
ProcFB: 0 mgag200drmfb
ProcKernelCmdLine: BOOT_IMAGE=/vmlinuz-5.15.0-122-generic
root=/dev/mapper/ubuntu--vg-ubuntu--lv ro
ProcVersionSignature: Ubuntu 5.15.0-122.132~20.04.1-generic 5.15.163
RelatedPackageVersions:
linux-restricted-modules-5.15.0-122-generic N/A
linux-backports-modules-5.15.0-122-generic N/A
linux-firmware 1.187.39
RfKill: Error: [Errno 2] No such file or directory: 'rfkill'
Tags: focal uec-images
Uname: Linux 5.15.0-122-generic x86_64
UnreportableReason: This report is about a package that is not installed.
UpgradeStatus: No upgrade log present (probably fresh install)
UserGroups: N/A
_MarkForUpload: False
dmi.bios.date: 09/17/2020
dmi.bios.release: 5.14
dmi.bios.vendor: Cisco Systems, Inc.
dmi.bios.version: C220M5.4.1.2b.0.0917201934
dmi.board.asset.tag: GT02175
dmi.board.name: UCSC-C220-M5SX
dmi.board.vendor: Cisco Systems Inc
dmi.board.version: 74-105772-01
dmi.chassis.asset.tag: GT02175
dmi.chassis.type: 23
dmi.chassis.vendor: Cisco Systems Inc
dmi.chassis.version: 74-105774-03
dmi.modalias:
dmi:bvnCiscoSystems,Inc.:bvrC220M5.4.1.2b.0.0917201934:bd09/17/2020:br5.14:svnCiscoSystemsInc:pnUCSC-C220-M5SX:pvrA0:rvnCiscoSystemsInc:rnUCSC-C220-M5SX:rvr74-105772-01:cvnCiscoSystemsInc:ct23:cvr74-105774-03:sku:
dmi.product.name: UCSC-C220-M5SX
dmi.product.version: A0
dmi.sys.vendor: Cisco Systems Inc
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