please enable CONFIG_ARM64_LSE_ATOMICS

[dann frazier]

[Impact]
Performance is lowered for ARM >= v8.1 cpus by not taking advantage of the "Large System Extenstion" atomic instructions they provide.

Note: This config was enabled during xenial development, but was disabled to workaround a FTBFS[*] due to us not having a new enough binutils to support it. binutils was later updated in xenial, and supports these instructions.

[Test Case]
grep CONFIG_ARM64_LSE_ATOMICS=y /boot/config-$(uname -r)

[Regression Risk]
There is a known small performance overhead for < ARMv8.1 arm64 systems (noted in the Kconfig). To mitigate the risk of runtime or build failures, this should be tested on both ARMv8 and >= ARMv8.1 systems, to exercise both code paths.

[*] https://answers.launchpad.net/~canonical-kernel-team/+archive/ubuntu/unstable/+build/8438034

[Brad Figg (brad-figg)]

This bug is missing log files that will aid in diagnosing the problem. From a terminal window please run:

apport-collect 1691614

and then change the status of the bug to 'Confirmed'.

If, due to the nature of the issue you have encountered, you are unable to run this command, please add a comment stating that fact and change the bug status to 'Confirmed'.

This change has been made by an automated script, maintained by the Ubuntu Kernel Team.

[dann frazier (dannf)]

I'm unaware of any systems that support LSE that are also supported by the hwe-{x,y,z} kernels. I'll therefore mark those as "Won't Fix" for those releases. If someone is aware of such a system - and can take on the testing of this change for those releases, we can reconsider.

[Launchpad Janitor (janitor)]

This bug was fixed in the package linux - 4.11.0-10.15

---------------
linux (4.11.0-10.15) artful; urgency=low

  * linux: 4.11.0-10.15 -proposed tracker (LP: #1701271)

  * Artful update to v4.11.8 stable release (LP: #1701269)
    - clk: sunxi-ng: a31: Correct lcd1-ch1 clock register offset
    - clk: sunxi-ng: v3s: Fix usb otg device reset bit
    - clk: sunxi-ng: sun5i: Fix ahb_bist_clk definition
    - xen/blkback: fix disconnect while I/Os in flight
    - xen-blkback: don't leak stack data via response ring
    - ALSA: firewire-lib: Fix stall of process context at packet error
    - ALSA: pcm: Don't treat NULL chmap as a fatal error
    - ALSA: hda - Add Coffelake PCI ID
    - ALSA: hda - Apply quirks to Broxton-T, too
    - fs/exec.c: account for argv/envp pointers
    - powerpc/perf: Fix oops when kthread execs user process
    - autofs: sanity check status reported with AUTOFS_DEV_IOCTL_FAIL
    - fs/dax.c: fix inefficiency in dax_writeback_mapping_range()
    - lib/cmdline.c: fix get_options() overflow while parsing ranges
    - perf/x86/intel: Add 1G DTLB load/store miss support for SKL
    - perf probe: Fix probe definition for inlined functions
    - KVM: x86: fix singlestepping over syscall
    - KVM: MIPS: Fix maybe-uninitialized build failure
    - KVM: s390: gaccess: fix real-space designation asce handling for gmap
      shadows
    - KVM: PPC: Book3S HV: Cope with host using large decrementer mode
    - KVM: PPC: Book3S HV: Preserve userspace HTM state properly
    - KVM: PPC: Book3S HV: Ignore timebase offset on POWER9 DD1
    - KVM: PPC: Book3S HV: Context-switch EBB registers properly
    - KVM: PPC: Book3S HV: Restore critical SPRs to host values on guest exit
    - KVM: PPC: Book3S HV: Save/restore host values of debug registers
    - CIFS: Improve readdir verbosity
    - CIFS: Fix some return values in case of error in 'crypt_message'
    - cxgb4: notify uP to route ctrlq compl to rdma rspq
    - HID: Add quirk for Dell PIXART OEM mouse
    - random: silence compiler warnings and fix race
    - signal: Only reschedule timers on signals timers have sent
    - powerpc/kprobes: Pause function_graph tracing during jprobes handling
    - powerpc/64s: Handle data breakpoints in Radix mode
    - Input: i8042 - add Fujitsu Lifebook AH544 to notimeout list
    - brcmfmac: add parameter to pass error code in firmware callback
    - brcmfmac: use firmware callback upon failure to load
    - brcmfmac: unbind all devices upon failure in firmware callback
    - time: Fix clock->read(clock) race around clocksource changes
    - time: Fix CLOCK_MONOTONIC_RAW sub-nanosecond accounting
    - arm64/vdso: Fix nsec handling for CLOCK_MONOTONIC_RAW
    - target: Fix kref->refcount underflow in transport_cmd_finish_abort
    - iscsi-target: Fix delayed logout processing greater than
      SECONDS_FOR_LOGOUT_COMP
    - iscsi-target: Reject immediate data underflow larger than SCSI transfer
      length
    - drm/radeon: add a PX quirk for another K53TK variant
    - drm/radeon: add a quirk for Toshiba Satellite L20-183
    - drm/amdgpu/atom: fix ps allocation size for EnableDispPowerGating
    - drm/amdgpu: adjust default display clock
   ...