[Ubuntu 16.04.1] RELEASE and ACQUIRE atomics on Power

[bugproxy]

Will Deacon proposed the RELEASE/ACQUIRE/RELAXED semantics for atomic operations(https://lkml.org/lkml/2015/8/6/498), which has been already merged in 4.3-rc1. More people tend to use it for better performance(https://lkml.org/lkml/2015/9/20/47). These semantics are proposed for better fitting the need of high scalability.

 However, the efficient implementation hasn't been merged yet. As we have a weaker memory order model on POWER, if we didn't implement these atomics efficently, there would be no benefit we can gain from these new operations.

A proposal of an efficient implemenation has been sent out to upstream(https://lkml.org/lkml/2015/9/16/527), hopefully will get merged. Still there may be more atomics having RELEASE and ACQUIRE semantics, and there need more effort to implement them correctly. Also, we need to spread these new atomic variants to LTC kernel team to understand what they can provide and how to use them.

> Was this feature already accepted upstream?

Not yet, still waiting to get into the maintainer's tree, but there is no obvious objection to this feature.

[Ubuntu Foundations Team Bug Bot (crichton)]

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[Breno Leitão (breno-leitao)]

This is still a working in progress on our side, mainly waiting the patches to get accepted upstream.

[Leann Ogasawara (leannogasawara)]

Thanks Breno. Assigning this to the Canonical kernel team for awareness at this time. Once the patches have landed upstream, please feel free to note them here. Thanks.

[Leann Ogasawara (leannogasawara)]

Hi Breno,

Seeing as we are a week before Kernel Freeze for Xenial, I wanted to check in here and see what the status is for these patches. Have these officially landed upstream and should we be picking them up for 16.04?

[Breno Leitão (breno-leitao)]

Hi Leann,

The patches were finally acccepted and they are on Linus' tree. They are:

56c08e6d226c powerpc: atomic: Implement acquire/release/relaxed variants for cmpxchg
26760fc19a7e powerpc: atomic: Implement acquire/release/relaxed variants for xchg
dc53617c4a3f powerpc: atomic: Implement atomic{, 64}_*_return_* variants
e1ab7f39d7e0 atomics: Allow architectures to define their own __atomic_op_* helpers

Thank you,
Breno

[Launchpad Janitor (janitor)]

This bug was fixed in the package linux - 4.4.0-18.34

---------------
linux (4.4.0-18.34) xenial; urgency=low

  [ Tim Gardner ]

  * Release Tracking Bug
    - LP: #1566868

  * [i915_bpo] Fix RC6 on SKL GT3 & GT4 (LP: #1564759)
    - SAUCE: i915_bpo: drm/i915/skl: Fix rc6 based gpu/system hang
    - SAUCE: i915_bpo: drm/i915/skl: Fix spurious gpu hang with gt3/gt4 revs

  * CONFIG_ARCH_ROCKCHIP not enabled in armhf generic kernel (LP: #1566283)
    - [Config] CONFIG_ARCH_ROCKCHIP=y

  * [Feature] Memory Bandwidth Monitoring (LP: #1397880)
    - perf/x86/cqm: Fix CQM handling of grouping events into a cache_group
    - perf/x86/cqm: Fix CQM memory leak and notifier leak
    - x86/cpufeature: Carve out X86_FEATURE_*
    - Merge branch 'timers-core-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip
    - x86/topology: Create logical package id
    - perf/x86/mbm: Add Intel Memory B/W Monitoring enumeration and init
    - perf/x86/mbm: Add memory bandwidth monitoring event management
    - perf/x86/mbm: Implement RMID recycling
    - perf/x86/mbm: Add support for MBM counter overflow handling

  * User namespace mount updates (LP: #1566505)
    - SAUCE: quota: Require that qids passed to dqget() be valid and map into s_user_ns
    - SAUCE: fs: Allow superblock owner to change ownership of inodes with unmappable ids
    - SAUCE: fuse: Don't initialize user_id or group_id in mount options
    - SAUCE: cgroup: Use a new super block when mounting in a cgroup namespace
    - SAUCE: fs: fix a posible leak of allocated superblock

  * [arm64] kernel BUG at /build/linux-StrpB2/linux-4.4.0/fs/ext4/inode.c:2394!
    (LP: #1566518)
    - arm64: Honour !PTE_WRITE in set_pte_at() for kernel mappings
    - arm64: Update PTE_RDONLY in set_pte_at() for PROT_NONE permission

  * [Feature]USB core and xHCI tasks for USB 3.1 SuperSpeedPlus (SSP) support
    for Alpine Ridge on SKL (LP: #1519623)
    - usb: define USB_SPEED_SUPER_PLUS speed for SuperSpeedPlus USB3.1 devices
    - usb: set USB 3.1 roothub device speed to USB_SPEED_SUPER_PLUS
    - usb: show speed "10000" in sysfs for USB 3.1 SuperSpeedPlus devices
    - usb: add device descriptor for usb 3.1 root hub
    - usb: Support USB 3.1 extended port status request
    - xhci: Make sure xhci handles USB_SPEED_SUPER_PLUS devices.
    - xhci: set roothub speed to USB_SPEED_SUPER_PLUS for USB3.1 capable controllers
    - xhci: USB 3.1 add default Speed Attributes to SuperSpeedPlus device capability
    - xhci: set slot context speed field to SuperSpeedPlus for USB 3.1 SSP devices
    - usb: Add USB3.1 SuperSpeedPlus Isoc Endpoint Companion descriptor
    - usb: Parse the new USB 3.1 SuperSpeedPlus Isoc endpoint companion descriptor
    - usb: Add USB 3.1 Precision time measurement capability descriptor support
    - xhci: refactor and cleanup endpoint initialization.
    - xhci: Add SuperSpeedPlus high bandwidth isoc support to xhci endpoints
    - xhci: cleanup isoc tranfers queuing code
    - xhci: Support extended burst isoc TRB structure used by xhci 1.1 for USB 3.1
    - SAUCE: (noup) usb: fix regression in SuperSpeed endpoint descriptor parsing

  * wrong/missing permissions for device f...