linux-kernel - Re: [PATCH 0/6] Switch arm64 over to qrwlock

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Message-ID: <9e2468c3-894e-1204-4578-3d8266c56d6c@arm.com>
Date:   Thu, 5 Oct 2017 17:12:44 -0500
From:   Jeremy Linton <jeremy.linton@....com>
To:     Will Deacon <will.deacon@....com>, linux-kernel@...r.kernel.org
Cc:     linux-arm-kernel@...ts.infradead.org, peterz@...radead.org,
        mingo@...hat.com, longman@...hat.com, boqun.feng@...il.com,
        paulmck@...ux.vnet.ibm.com
Subject: Re: [PATCH 0/6] Switch arm64 over to qrwlock

Hi,


On 10/05/2017 07:54 AM, Will Deacon wrote:
> 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!

I haven't done any perf testing, but the machines continue to boot, and 
the stress-ng test which causes task lock problems with the normal arm64 
rwlock now appears to run as expected. So, its a good start!



> 
> 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(-)
>