Can you collect the following: Backing device baseline (it's possible the underlying disks regressed instead of the bcache layer). the same fio randrw test against the underlying backing device with bcache disabled
And with bcache enabled on both setups before and after tuning: 1) grep -r . /sys/class/block/bcache*/bcache/ > bdev_stats 2) grep -r . /sys/fs/bcache/*-*-*-*-*/ > cdev_stats 3) grep -r . /sys/class/block/sd?/queue/scheduler > bdev_schedulers -- You received this bug notification because you are a member of Kernel Packages, which is subscribed to linux in Ubuntu. https://bugs.launchpad.net/bugs/1806015 Title: bcache: performance regression without tuning under bionic Status in linux package in Ubuntu: Confirmed Bug description: 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. To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1806015/+subscriptions -- Mailing list: https://launchpad.net/~kernel-packages Post to : kernel-packages@lists.launchpad.net Unsubscribe : https://launchpad.net/~kernel-packages More help : https://help.launchpad.net/ListHelp
