linux-kernel - Re: [RFC PATCH 0/3] arm64: queued spinlocks and rw-locks

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Date:   Wed, 12 Apr 2017 13:04:55 -0400
From:   Adam Wallis <awallis@...eaurora.org>
To:     Yury Norov <ynorov@...iumnetworks.com>,
        linux-kernel@...r.kernel.org, linux-arch@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org
Cc:     Arnd Bergmann <arnd@...db.de>,
        Peter Zijlstra <peterz@...radead.org>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will.deacon@....com>,
        Jan Glauber <jglauber@...ium.com>,
        Ingo Molnar <mingo@...hat.com>, jason.low2@...com
Subject: Re: [RFC PATCH 0/3] arm64: queued spinlocks and rw-locks

On 4/10/2017 5:35 PM, Yury Norov wrote:
> The patch of Jan Glauber enables queued spinlocks on arm64. I rebased it on
> latest kernel sources, and added a couple of fixes to headers to apply it 
> smoothly.
> 
> Though, locktourture test shows significant performance degradation in the
> acquisition of rw-lock for read on qemu:
> 
>                           Before           After
> spin_lock-torture:      38957034        37076367         -4.83
> rw_lock-torture W:       5369471        18971957        253.33
> rw_lock-torture R:       6413179         3668160        -42.80
> 

On our 48 core QDF2400 part, I am seeing huge improvements with these patches on
the torture tests. The improvements go up even further when I apply Jason Low's
MCS Spinlock patch: https://lkml.org/lkml/2016/4/20/725

> I'm  not much experienced in locking, and so wonder how it's possible that
> simple switching to generic queued rw-lock causes so significant performance
> degradation, while in theory it should improve it. Even more, on x86 there
> are no such problems probably.
> 
> I also think that patches 1 and 2 are correct and useful, and should be applied
> anyway.
> 
> Any comments appreciated.
> 
> Yury.
> 

I will be happy to tests these patches more thoroughly after you get some
additional comments/feedback.

> Jan Glauber (1):
>   arm64/locking: qspinlocks and qrwlocks support
> 
> Yury Norov (2):
>   kernel/locking: #include <asm/spinlock.h> in qrwlock.c
>   asm-generic: don't #include <linux/atomic.h> in qspinlock_types.h
> 
>  arch/arm64/Kconfig                      |  2 ++
>  arch/arm64/include/asm/qrwlock.h        |  7 +++++++
>  arch/arm64/include/asm/qspinlock.h      | 20 ++++++++++++++++++++
>  arch/arm64/include/asm/spinlock.h       | 12 ++++++++++++
>  arch/arm64/include/asm/spinlock_types.h | 14 +++++++++++---
>  include/asm-generic/qspinlock.h         |  1 +
>  include/asm-generic/qspinlock_types.h   |  8 --------
>  kernel/locking/qrwlock.c                |  1 +
>  8 files changed, 54 insertions(+), 11 deletions(-)
>  create mode 100644 arch/arm64/include/asm/qrwlock.h
>  create mode 100644 arch/arm64/include/asm/qspinlock.h
> 

Thanks

-- 
Adam Wallis
Qualcomm Datacenter Technologies as an affiliate of Qualcomm Technologies, Inc.
Qualcomm Technologies, Inc. is a member of the Code Aurora Forum,
a Linux Foundation Collaborative Project.