Public bug reported:
Whilst diagnosing a disk performance issue on our QA cloud, I did some
performance testing of bcache fronted spindles to compare xenial (4.4
kernel) and bionic (4.14 kernel) installs on the same hardware.
A vanilla install (with no tuning of bcache configuration) resulted in
the following performance metrics (using the sysbench fileio rndrw
benchmark):
Xenial
4 threads:
45.77 MiB/sec read
30.52 MiB/sec write
48 threads (matching core count):
138.72 MiB/sec read
92.52 MiB/sec write
Bionic
4 threads:
29.51 MiB/sec
19.67 MiB/sec
48 threads (matching core count):
41.35 MiB/sec
27.59 MiB/sec
After tuning (disabling the congested_{read|write}_threshold_us and
disabling sequential cutoff)
Xenial
48 threads (matching core count):
153.60 MiB/sec
102.40 MiB/sec
Bionic
48 threads (matching core count):
161.49 MiB/sec
107.67 MiB/sec
suggestion is this might be something todo with the move from deadline to cfq
as the default IO scheduler between 4.4 and 4.13 but as you can see
the baseline vanilla performance is significantly slower.
As a further reference point, the IO performance on the NVMe device
supporting the bcache device is:
4 threads:
554.56 MiB/sec read
369.71 MiB/sec write
ProblemType: Bug
DistroRelease: Ubuntu 18.04
Package: linux-image-generic 4.15.0.39.41
ProcVersionSignature: Ubuntu 4.15.0-39.42-generic 4.15.18
Uname: Linux 4.15.0-39-generic x86_64
AlsaDevices:
total 0
crw-rw---- 1 root audio 116, 1 Nov 29 11:38 seq
crw-rw---- 1 root audio 116, 33 Nov 29 11:38 timer
AplayDevices: Error: [Errno 2] No such file or directory: 'aplay': 'aplay'
ApportVersion: 2.20.9-0ubuntu7.5
Architecture: amd64
ArecordDevices: Error: [Errno 2] No such file or directory: 'arecord': 'arecord'
AudioDevicesInUse: Error: command ['fuser', '-v', '/dev/snd/seq',
'/dev/snd/timer'] failed with exit code 1:
Date: Fri Nov 30 10:11:54 2018
IwConfig: Error: [Errno 2] No such file or directory: 'iwconfig': 'iwconfig'
Lsusb:
Bus 002 Device 002: ID 8087:8002 Intel Corp.
Bus 002 Device 001: ID 1d6b:0002 Linux Foundation 2.0 root hub
Bus 001 Device 003: ID 413c:a001 Dell Computer Corp. Hub
Bus 001 Device 002: ID 8087:800a Intel Corp.
Bus 001 Device 001: ID 1d6b:0002 Linux Foundation 2.0 root hub
MachineType: Dell Inc. PowerEdge R630
PciMultimedia:
ProcEnviron:
TERM=xterm-256color
PATH=(custom, no user)
XDG_RUNTIME_DIR=<set>
LANG=C.UTF-8
SHELL=/bin/bash
ProcFB: 0 mgadrmfb
ProcKernelCmdLine: BOOT_IMAGE=/vmlinuz-4.15.0-39-generic
root=UUID=a361a524-47eb-46c3-8a04-e5eaa65188c9 ro hugepages=103117 iommu=pt
intel_iommu=on
RelatedPackageVersions:
linux-restricted-modules-4.15.0-39-generic N/A
linux-backports-modules-4.15.0-39-generic N/A
linux-firmware 1.173.2
RfKill: Error: [Errno 2] No such file or directory: 'rfkill': 'rfkill'
SourcePackage: linux
UpgradeStatus: No upgrade log present (probably fresh install)
dmi.bios.date: 11/08/2016
dmi.bios.vendor: Dell Inc.
dmi.bios.version: 2.3.4
dmi.board.name: 02C2CP
dmi.board.vendor: Dell Inc.
dmi.board.version: A03
dmi.chassis.type: 23
dmi.chassis.vendor: Dell Inc.
dmi.modalias:
dmi:bvnDellInc.:bvr2.3.4:bd11/08/2016:svnDellInc.:pnPowerEdgeR630:pvr:rvnDellInc.:rn02C2CP:rvrA03:cvnDellInc.:ct23:cvr:
dmi.product.name: PowerEdge R630
dmi.sys.vendor: Dell Inc.
** Affects: linux (Ubuntu)
Importance: Undecided
Status: Confirmed
** Tags: amd64 apport-bug bionic uec-images
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https://bugs.launchpad.net/bugs/1806015
Title:
bcache: performance regression without tuning under bionic
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