linux-kernel - Re: [PATCH v3 0/6] powerpc: queued spinlocks and rwlocks

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Date:   Mon, 6 Jul 2020 14:39:53 -0400
From:   Waiman Long <longman@...hat.com>
To:     Nicholas Piggin <npiggin@...il.com>, linuxppc-dev@...ts.ozlabs.org
Cc:     Will Deacon <will@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Boqun Feng <boqun.feng@...il.com>,
        Ingo Molnar <mingo@...hat.com>,
        Anton Blanchard <anton@...abs.org>,
        linux-kernel@...r.kernel.org,
        virtualization@...ts.linux-foundation.org, kvm-ppc@...r.kernel.org,
        linux-arch@...r.kernel.org
Subject: Re: [PATCH v3 0/6] powerpc: queued spinlocks and rwlocks

On 7/6/20 12:35 AM, Nicholas Piggin wrote:
> v3 is updated to use __pv_queued_spin_unlock, noticed by Waiman (thank you).
>
> Thanks,
> Nick
>
> Nicholas Piggin (6):
>    powerpc/powernv: must include hvcall.h to get PAPR defines
>    powerpc/pseries: move some PAPR paravirt functions to their own file
>    powerpc: move spinlock implementation to simple_spinlock
>    powerpc/64s: implement queued spinlocks and rwlocks
>    powerpc/pseries: implement paravirt qspinlocks for SPLPAR
>    powerpc/qspinlock: optimised atomic_try_cmpxchg_lock that adds the
>      lock hint
>
>   arch/powerpc/Kconfig                          |  13 +
>   arch/powerpc/include/asm/Kbuild               |   2 +
>   arch/powerpc/include/asm/atomic.h             |  28 ++
>   arch/powerpc/include/asm/paravirt.h           |  89 +++++
>   arch/powerpc/include/asm/qspinlock.h          |  91 ++++++
>   arch/powerpc/include/asm/qspinlock_paravirt.h |   7 +
>   arch/powerpc/include/asm/simple_spinlock.h    | 292 +++++++++++++++++
>   .../include/asm/simple_spinlock_types.h       |  21 ++
>   arch/powerpc/include/asm/spinlock.h           | 308 +-----------------
>   arch/powerpc/include/asm/spinlock_types.h     |  17 +-
>   arch/powerpc/lib/Makefile                     |   3 +
>   arch/powerpc/lib/locks.c                      |  12 +-
>   arch/powerpc/platforms/powernv/pci-ioda-tce.c |   1 +
>   arch/powerpc/platforms/pseries/Kconfig        |   5 +
>   arch/powerpc/platforms/pseries/setup.c        |   6 +-
>   include/asm-generic/qspinlock.h               |   4 +
>   16 files changed, 577 insertions(+), 322 deletions(-)
>   create mode 100644 arch/powerpc/include/asm/paravirt.h
>   create mode 100644 arch/powerpc/include/asm/qspinlock.h
>   create mode 100644 arch/powerpc/include/asm/qspinlock_paravirt.h
>   create mode 100644 arch/powerpc/include/asm/simple_spinlock.h
>   create mode 100644 arch/powerpc/include/asm/simple_spinlock_types.h
>
This patch looks OK to me.

I had run some microbenchmark on powerpc system with or w/o the patch.

On a 2-socket 160-thread SMT4 POWER9 system (not virtualized):

5.8.0-rc4
=========

Running locktest with spinlock [runtime = 10s, load = 1]
Threads = 160, Min/Mean/Max = 77,665/90,153/106,895
Threads = 160, Total Rate = 1,441,759 op/s; Percpu Rate = 9,011 op/s

Running locktest with rwlock [runtime = 10s, r% = 50%, load = 1]
Threads = 160, Min/Mean/Max = 47,879/53,807/63,689
Threads = 160, Total Rate = 860,192 op/s; Percpu Rate = 5,376 op/s

Running locktest with spinlock [runtime = 10s, load = 1]
Threads = 80, Min/Mean/Max = 242,907/319,514/463,161
Threads = 80, Total Rate = 2,555 kop/s; Percpu Rate = 32 kop/s

Running locktest with rwlock [runtime = 10s, r% = 50%, load = 1]
Threads = 80, Min/Mean/Max = 146,161/187,474/259,270
Threads = 80, Total Rate = 1,498 kop/s; Percpu Rate = 19 kop/s

Running locktest with spinlock [runtime = 10s, load = 1]
Threads = 40, Min/Mean/Max = 646,639/1,000,817/1,455,205
Threads = 40, Total Rate = 4,001 kop/s; Percpu Rate = 100 kop/s

Running locktest with rwlock [runtime = 10s, r% = 50%, load = 1]
Threads = 40, Min/Mean/Max = 402,165/597,132/814,555
Threads = 40, Total Rate = 2,388 kop/s; Percpu Rate = 60 kop/s

5.8.0-rc4-qlock+
================

Running locktest with spinlock [runtime = 10s, load = 1]
Threads = 160, Min/Mean/Max = 123,835/124,580/124,587
Threads = 160, Total Rate = 1,992 kop/s; Percpu Rate = 12 kop/s

Running locktest with rwlock [runtime = 10s, r% = 50%, load = 1]
Threads = 160, Min/Mean/Max = 254,210/264,714/276,784
Threads = 160, Total Rate = 4,231 kop/s; Percpu Rate = 26 kop/s

Running locktest with spinlock [runtime = 10s, load = 1]
Threads = 80, Min/Mean/Max = 599,715/603,397/603,450
Threads = 80, Total Rate = 4,825 kop/s; Percpu Rate = 60 kop/s

Running locktest with rwlock [runtime = 10s, r% = 50%, load = 1]
Threads = 80, Min/Mean/Max = 492,687/525,224/567,456
Threads = 80, Total Rate = 4,199 kop/s; Percpu Rate = 52 kop/s

Running locktest with spinlock [runtime = 10s, load = 1]
Threads = 40, Min/Mean/Max = 1,325,623/1,325,628/1,325,636
Threads = 40, Total Rate = 5,299 kop/s; Percpu Rate = 132 kop/s

Running locktest with rwlock [runtime = 10s, r% = 50%, load = 1]
Threads = 40, Min/Mean/Max = 1,249,731/1,292,977/1,342,815
Threads = 40, Total Rate = 5,168 kop/s; Percpu Rate = 129 kop/s

On systems on large number of cpus, qspinlock lock is faster and more fair.

With some tuning, we may be able to squeeze out more performance.

Cheers,
Longman