From: Sebastian Andrzej Siewior <sebastian@breakpoint.cc>
To: Will Deacon <will@kernel.org>
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: Thu, 17 Oct 2019 00:09:31 +0200 [thread overview]
Message-ID: <20191016220927.54ptu5etl3la3pdb@flow> (raw)
In-Reply-To: <20191016155755.66ges3ybn3awx45l@willie-the-truck>
On 2019-10-16 16:57:56 [+0100], Will Deacon wrote:
> Hi Sebastian,
Hi Will,
> 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.
Waiman had numbers on x86 on how good this q-lock thingy is and x86
moved to this. ARM64 didn't state a reason in particular only saying
"it served us well but we do q-locks now" (this is how I remember it
after I went over the git logs some time ago).
Not knowing anything about qspin vs ticket locking I looked on how hard
will be to switch. Then I looked with hackbench at it to see if it was
worth it and it didn't look that bad. Plus the diffstat was negative so…
> 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.
Okay. Let me see what I can do.
> Will
Sebastian
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next prev parent reply other threads:[~2019-10-16 22:09 UTC|newest]
Thread overview: 22+ 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
2019-10-14 7:25 ` Arnd Bergmann
2019-10-15 22:31 ` [PATCH 1/6 v2] " 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
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 [this message]
2019-10-17 15:36 ` Waiman Long
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