** Description changed: 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 - ... + 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: + + https://bit.ly/2BtN52W + ... + 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 + https://bit.ly/2BtN52W + https://bit.ly/2BtN52W 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?
-- You received this bug notification because you are a member of Ubuntu Bugs, which is subscribed to Ubuntu. https://bugs.launchpad.net/bugs/1815733 Title: unnecessary request_queue freeze To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu/+bug/1815733/+subscriptions -- ubuntu-bugs mailing list ubuntu-bugs@lists.ubuntu.com https://lists.ubuntu.com/mailman/listinfo/ubuntu-bugs
