I've tested this kernel - there's no latency spike when setting none scheduler while it's already none - nice.
Waiting for e5fa81408fb43ebabde65938ef8b20ae879017e7 backport:) -- 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/1815733 Title: unnecessary request_queue freeze Status in linux package in Ubuntu: Incomplete Bug description: Hi all, In linux-4.15, which is used as hwe-edge in xenial, there's an unexpected behavior. It results in latency spikes of generic_make_request() function call. How to reproduce: 1. Run fio: fio --name=test --rw=randwrite --direct=1 --filename=/dev/sdt --iodepth=1 --fsync=1 --ioengine=libaio --write_lat_log loglat 2. While fio is writing to the device, change nr_requests setting to the same value as current: echo 256 > /sys/block/sdt/queue/nr_requests or: if scheduler is already none: echo none > /sys/block/sdt/queue/scheduler 3. Stop fio and check slat log: ... 3980, 16, 1, 4096 3999, 17, 1, 4096 4010, 19, 1, 4096 4020, 18, 1, 4096 4045, 10821, 1, 4096 4054, 25, 1, 4096 4070, 12, 1, 4096 4083, 17, 1, 4096 4094, 16, 1, 4096 4111, 17, 1, 4096 ... There're a few patches to fix this behavior: https://git.kernel.org/pub/scm/linux/kernel/git/axboe/linux-block.git/commit/?h=for-5.1/block&id=e5fa81408fb43ebabde65938ef8b20ae879017e7 https://git.kernel.org/pub/scm/linux/kernel/git/axboe/linux-block.git/commit/?h=for-5.1/block&id=fbd72127c975dc8e532ecc73d52f3b1b00935bec This behavior affects production systems, because every change uevent triggers udev to change settings prior to udev rules. Some software, for example arcconf (tool for managing adaptec HBA adapters) triggers uevents for every block device. So, every call to arcconf utility results in latency spike. Could this be backported to 4.15 kernel for xenial/bionic? To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1815733/+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
