From: Will Deacon <will@kernel.org>
To: Sebastian Andrzej Siewior <sebastian@breakpoint.cc>
Cc: Arnd Bergmann <arnd@arndb.de>,
Peter Zijlstra <peterz@infradead.org>,
Russell King <linux@armlinux.org.uk>,
Ingo Molnar <mingo@redhat.com>, Waiman Long <longman@redhat.com>,
linux-arm-kernel@lists.infradead.org
Subject: Re: [RFC PATCH 0/6 v2] Queued spinlocks/RW-locks for ARM
Date: Wed, 16 Oct 2019 16:57:56 +0100 [thread overview]
Message-ID: <20191016155755.66ges3ybn3awx45l@willie-the-truck> (raw)
In-Reply-To: <20191013221310.30748-1-sebastian@breakpoint.cc>
Hi Sebastian,
On Mon, Oct 14, 2019 at 12:13:04AM +0200, Sebastian Andrzej Siewior wrote:
> I added support for queued-RW and -spinlocks for ARM. I followed Arnd's
> suggestion and added support for xchg() on 8bit and 16bit variables (V6
> CPUs) via the SH implementation. This makes it possible to remove the
> current ticket based locking implementation.
>
> The numbers should be the same as in v1 posted here:
> http://lkml.kernel.org/r/20191007214439.27891-1-sebastian@breakpoint.cc
>
> The only thing changed is that patch #1-#3 wire up the missing xchg and
> the patches #4 and #5 additionally remove the old implementation while
> adding the missing bits for the queued implementation.
To be honest with you, I'm surprised that qspinlock is worth it for 32-bit
Arm. qrwlock makes sense because of fairness and starvation issues, but in
my benchmarks on arm64 tickets tended to perform at least as well for small
core counts, and I think that's largely going to be true for systems
running a 32-bit kernel.
I've uploaded my (crude, was never meant to be shared!) benchmark harness
here:
https://mirrors.edge.kernel.org/pub/linux/kernel/people/will/spinbench
which I used to generate graphs like:
https://mirrors.edge.kernel.org/pub/linux/kernel/people/will/slides/arm64-spinlocks.pdf
Maybe you could port it to 32-bit and see what the numbers look like? The
qspinlock code probably needs re-syncing with mainline too, but see how you
go. If it ends up being useful maybe I'll host it in a git tree.
Will
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next prev parent reply other threads:[~2019-10-16 15:58 UTC|newest]
Thread overview: 30+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-10-13 22:13 [RFC PATCH 0/6 v2] Queued spinlocks/RW-locks for ARM Sebastian Andrzej Siewior
2019-10-13 22:13 ` [PATCH 1/6] sh: Move cmpxchg-xchg.h to asm-generic Sebastian Andrzej Siewior
2019-10-13 22:13 ` Sebastian Andrzej Siewior
2019-10-13 22:13 ` Sebastian Andrzej Siewior
2019-10-13 22:13 ` Sebastian Andrzej Siewior
2019-10-14 7:25 ` Arnd Bergmann
2019-10-14 7:25 ` Arnd Bergmann
2019-10-14 7:25 ` Arnd Bergmann
2019-10-14 7:25 ` Arnd Bergmann
2019-10-15 22:31 ` [PATCH 1/6 v2] " Sebastian Andrzej Siewior
2019-10-15 22:31 ` Sebastian Andrzej Siewior
2019-10-15 22:31 ` Sebastian Andrzej Siewior
2019-10-13 22:13 ` [PATCH 2/6] ARM: cmpxchg: Define first cmpxchg() followed by xchg() Sebastian Andrzej Siewior
2019-10-13 22:13 ` [PATCH 3/6] ARM: Add xchg_{8|16}() on generic cmpxchg() on CPU_V6 Sebastian Andrzej Siewior
2019-10-13 22:13 ` [PATCH 4/6] ARM: Use qrwlock implementation Sebastian Andrzej Siewior
2019-10-13 22:13 ` [PATCH 5/6] ARM: Use qspinlock implementation Sebastian Andrzej Siewior
2019-10-13 22:13 ` [PATCH 6/6] ARM: Inline locking functions for !PREEMPTION Sebastian Andrzej Siewior
2019-10-14 7:43 ` Arnd Bergmann
2019-10-14 10:01 ` Arnd Bergmann
2019-10-15 22:30 ` Sebastian Andrzej Siewior
2019-10-15 22:37 ` Waiman Long
2019-10-15 22:47 ` Arnd Bergmann
2019-10-15 22:04 ` Sebastian Andrzej Siewior
2019-10-14 9:00 ` [RFC PATCH 0/6 v2] Queued spinlocks/RW-locks for ARM Arnd Bergmann
2019-10-16 15:57 ` Will Deacon [this message]
2019-10-16 17:45 ` Waiman Long
2019-10-16 18:33 ` Arnd Bergmann
2019-10-16 21:35 ` Sebastian Andrzej Siewior
2019-10-16 22:09 ` Sebastian Andrzej Siewior
2019-10-17 15:36 ` Waiman Long
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