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    Subject[GIT PULL v2 0/5] cpu_relax: drop lowlatency, introduce yield
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    Peter,

    here is v2 with some improved patch descriptions and some fixes. The
    previous version has survived one day of linux-next and I only changed
    small parts.
    So unless there is some other issue, feel free to pull (or to apply
    the patches) to tip/locking.

    The following changes since commit 07d9a380680d1c0eb51ef87ff2eab5c994949e69:

    Linux 4.9-rc2 (2016-10-23 17:10:14 -0700)

    are available in the git repository at:

    git://git.kernel.org/pub/scm/linux/kernel/git/borntraeger/linux.git tags/cpurelax

    for you to fetch changes up to dcc37f9044436438360402714b7544a8e8779b07:

    processor.h: remove cpu_relax_lowlatency (2016-10-25 09:49:57 +0200)

    ----------------------------------------------------------------
    cpu_relax: drop lowlatency, introduce yield

    For spinning loops people do often use barrier() or cpu_relax().
    For most architectures cpu_relax and barrier are the same, but on
    some architectures cpu_relax can add some latency.
    For example on power,sparc64 and arc, cpu_relax can shift the CPU
    towards other hardware threads in an SMT environment.
    On s390 cpu_relax does even more, it uses an hypercall to the
    hypervisor to give up the timeslice.
    In contrast to the SMT yielding this can result in larger latencies.
    In some places this latency is unwanted, so another variant
    "cpu_relax_lowlatency" was introduced. Before this is used in more
    and more places, lets revert the logic and provide a cpu_relax_yield
    that can be called in places where yielding is more important than
    latency. By default this is the same as cpu_relax on all architectures.

    So my proposal boils down to:
    - lowest latency: use barrier() or mb() if necessary
    - low latency: use cpu_relax (e.g. might give up some cpu for the other
    _hardware_ threads)
    - really give up CPU: use cpu_relax_yield

    PS: In the long run I would also try to provide for s390 something
    like cpu_relax_yield_to with a cpu number (or just add that to
    cpu_relax_yield), since a yield_to is always better than a yield as
    long as we know the waiter.

    ----------------------------------------------------------------
    Christian Borntraeger (5):
    processor.h: introduce cpu_relax_yield
    stop_machine: yield CPU during stop machine
    s390: make cpu_relax a barrier again
    processor.h: Remove cpu_relax_lowlatency users
    processor.h: remove cpu_relax_lowlatency

    arch/alpha/include/asm/processor.h | 2 +-
    arch/arc/include/asm/processor.h | 4 ++--
    arch/arm/include/asm/processor.h | 2 +-
    arch/arm64/include/asm/processor.h | 2 +-
    arch/avr32/include/asm/processor.h | 2 +-
    arch/blackfin/include/asm/processor.h | 2 +-
    arch/c6x/include/asm/processor.h | 2 +-
    arch/cris/include/asm/processor.h | 2 +-
    arch/frv/include/asm/processor.h | 2 +-
    arch/h8300/include/asm/processor.h | 2 +-
    arch/hexagon/include/asm/processor.h | 2 +-
    arch/ia64/include/asm/processor.h | 2 +-
    arch/m32r/include/asm/processor.h | 2 +-
    arch/m68k/include/asm/processor.h | 2 +-
    arch/metag/include/asm/processor.h | 2 +-
    arch/microblaze/include/asm/processor.h | 2 +-
    arch/mips/include/asm/processor.h | 2 +-
    arch/mn10300/include/asm/processor.h | 2 +-
    arch/nios2/include/asm/processor.h | 2 +-
    arch/openrisc/include/asm/processor.h | 2 +-
    arch/parisc/include/asm/processor.h | 2 +-
    arch/powerpc/include/asm/processor.h | 2 +-
    arch/s390/include/asm/processor.h | 4 ++--
    arch/s390/kernel/processor.c | 4 ++--
    arch/score/include/asm/processor.h | 2 +-
    arch/sh/include/asm/processor.h | 2 +-
    arch/sparc/include/asm/processor_32.h | 2 +-
    arch/sparc/include/asm/processor_64.h | 2 +-
    arch/tile/include/asm/processor.h | 2 +-
    arch/unicore32/include/asm/processor.h | 2 +-
    arch/x86/include/asm/processor.h | 2 +-
    arch/x86/um/asm/processor.h | 2 +-
    arch/xtensa/include/asm/processor.h | 2 +-
    drivers/gpu/drm/i915/i915_gem_request.c | 2 +-
    drivers/vhost/net.c | 4 ++--
    kernel/locking/mcs_spinlock.h | 4 ++--
    kernel/locking/mutex.c | 4 ++--
    kernel/locking/osq_lock.c | 6 +++---
    kernel/locking/qrwlock.c | 6 +++---
    kernel/locking/rwsem-xadd.c | 4 ++--
    kernel/stop_machine.c | 2 +-
    lib/lockref.c | 2 +-
    42 files changed, 53 insertions(+), 53 deletions(-)

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