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    SubjectRe: [PATCH 0/6] Switch arm64 over to qrwlock
    2017-10-05 14:54 GMT+02:00 Will Deacon <will.deacon@arm.com>:
    >
    > Hi all,
    >
    > This patch series reworks bits of the qrwlock code that it can be used
    > to replace the asm rwlocks currently implemented for arm64. The structure
    > of the series is:
    >
    > Patches 1-3 : Work WFE into qrwlock using atomic_cond_read_acquire so
    > we can avoid busy-waiting.
    >
    > Patch 4 : Enable qrwlocks for arm64
    >
    > Patch 5-6 : Ensure writer slowpath fairness. This has a potential
    > performance impact on the writer unlock path, so I've
    > kept them at the end.
    >
    > The patches apply on top of my other locking cleanups:
    >
    > http://lkml.kernel.org/r/1507055129-12300-1-git-send-email-will.deacon@arm.com
    >
    > although the conflict with mainline is trivial to resolve without those.
    > The full stack is also pushed here:
    >
    > git://git.kernel.org/pub/scm/linux/kernel/git/will/linux.git qrwlock
    >
    > All comments (particularly related to testing and performance) welcome!

    Hi Will,

    run your patches on ThunderX2.

    Old RW locks:

    insmod ./locktorture.ko nwriters_stress=56 nreaders_stress=224
    torture_type="rw_lock_irq" stat_interval=2

    [ 558.700042] Writes: Total: 10127 Max/Min: 0/0 Fail: 0
    [ 558.700054] Reads : Total: 764714 Max/Min: 0/0 Fail: 0
    [ 561.797011] Writes: Total: 11288 Max/Min: 0/0 Fail: 0
    [ 561.802518] Reads : Total: 2104452 Max/Min: 0/0 Fail: 0
    [ 565.844219] Writes: Total: 11512 Max/Min: 0/0 Fail: 0
    [ 565.849710] Reads : Total: 4277492 Max/Min: 0/0 Fail: 0

    Queued RW locks:

    [ 221.491207] Writes: Total: 57318 Max/Min: 0/0 Fail: 0
    [ 221.491219] Reads : Total: 382979 Max/Min: 0/0 Fail: 0
    [ 223.507065] Writes: Total: 83490 Max/Min: 0/0 Fail: 0
    [ 223.512611] Reads : Total: 684848 Max/Min: 0/0 Fail: 0
    [ 225.522937] Writes: Total: 110012 Max/Min: 0/0 Fail: 0
    [ 225.528511] Reads : Total: 968826 Max/Min: 0/0 Fail: 0

    So readers are still preferred over writers, but results are _way_
    better. Also, with the old implementation
    above test hung the machine which does not happen with the queued variant.

    If you want you can add:
    Tested-by: Jan Glauber <jglauber@cavium.com>

    --Jan

    > Cheers,
    >
    > Will
    >
    > --->8
    >
    > Will Deacon (6):
    > kernel/locking: Use struct qrwlock instead of struct __qrwlock
    > locking/atomic: Add atomic_cond_read_acquire
    > kernel/locking: Use atomic_cond_read_acquire when spinning in qrwlock
    > arm64: locking: Move rwlock implementation over to qrwlocks
    > kernel/locking: Prevent slowpath writers getting held up by fastpath
    > kernel/locking: Remove unused union members from struct qrwlock
    >
    > arch/arm64/Kconfig | 17 ++++
    > arch/arm64/include/asm/Kbuild | 1 +
    > arch/arm64/include/asm/spinlock.h | 164 +-------------------------------
    > arch/arm64/include/asm/spinlock_types.h | 6 +-
    > include/asm-generic/atomic-long.h | 3 +
    > include/asm-generic/qrwlock.h | 14 +--
    > include/asm-generic/qrwlock_types.h | 2 +-
    > include/linux/atomic.h | 4 +
    > kernel/locking/qrwlock.c | 83 +++-------------
    > 9 files changed, 43 insertions(+), 251 deletions(-)
    >
    > --
    > 2.1.4
    >

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