From: Arnd Bergmann <arnd@arndb.de>
To: Huacai Chen <chenhuacai@loongson.cn>
Cc: Peter Zijlstra <peterz@infradead.org>,
Ingo Molnar <mingo@redhat.com>, Will Deacon <will@kernel.org>,
Arnd Bergmann <arnd@arndb.de>, Waiman Long <longman@redhat.com>,
Boqun Feng <boqun.feng@gmail.com>, Guo Ren <guoren@kernel.org>,
linux-arch <linux-arch@vger.kernel.org>,
Rui Wang <wangrui@loongson.cn>,
Xuefeng Li <lixuefeng@loongson.cn>,
Huacai Chen <chenhuacai@gmail.com>,
Jiaxun Yang <jiaxun.yang@flygoat.com>
Subject: Re: [PATCH RFC 1/2] arch: Introduce ARCH_HAS_HW_XCHG_SMALL
Date: Sat, 24 Jul 2021 21:24:10 +0200 [thread overview]
Message-ID: <CAK8P3a0ZabB0cBR_SnOhi2=qxdQOYPGPEJeOqV0em1+bsvZKWw@mail.gmail.com> (raw)
In-Reply-To: <20210724123617.3525377-1-chenhuacai@loongson.cn>
On Sat, Jul 24, 2021 at 2:36 PM Huacai Chen <chenhuacai@loongson.cn> wrote:
>
> Introduce a new Kconfig option ARCH_HAS_HW_XCHG_SMALL, which means arch
> has hardware sub-word xchg/cmpxchg support. This option will be used as
> an indicator to select the bit-field definition in the qspinlock data
> structure.
>
> Signed-off-by: Huacai Chen <chenhuacai@loongson.cn>
Adding a Kconfig conditional sounds like a good idea, but I have two
concerns about the specific implementation:
- I think we should have separate symbols for 8-bit, 16-bit and 64-bit
cmpxchg(). I think every architecture needs to support at least 32-bit
cmpxchg() and 64-bit architectures also need to support cmpxchg64().
I actually have a prototype patch that introduces cmpxchg8() and
cmpxchg16() helpers with the purpose of no longer supporting these
width in the normal cmpxchg(), but that is mostly independent of
whether we want a conditional or not.
- If I remember correctly, there were some concerns about whether using
this information for picking the qspinlock implementation is a good idea.
Arnd
next prev parent reply other threads:[~2021-07-24 19:24 UTC|newest]
Thread overview: 26+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-07-24 12:36 [PATCH RFC 1/2] arch: Introduce ARCH_HAS_HW_XCHG_SMALL Huacai Chen
2021-07-24 12:36 ` [PATCH RFC 2/2] qspinlock: Use ARCH_HAS_HW_XCHG_SMALL to select _Q_PENDING_BITS definition Huacai Chen
2021-07-24 19:24 ` Arnd Bergmann [this message]
2021-07-25 3:06 ` [PATCH RFC 1/2] arch: Introduce ARCH_HAS_HW_XCHG_SMALL Jiaxun Yang
2021-07-25 10:08 ` Arnd Bergmann
2021-07-26 8:36 ` Geert Uytterhoeven
2021-07-26 8:56 ` Huacai Chen
2021-07-26 10:39 ` Boqun Feng
2021-07-26 16:41 ` Guo Ren
2021-07-26 17:03 ` Boqun Feng
2021-07-26 21:20 ` Waiman Long
2021-07-27 1:27 ` Guo Ren
2021-07-27 2:29 ` Boqun Feng
2021-07-27 2:46 ` Waiman Long
2021-07-27 11:05 ` Peter Zijlstra
2021-07-28 10:40 ` Huacai Chen
2021-07-28 11:01 ` Peter Zijlstra
2021-07-29 16:38 ` Huacai Chen
2021-07-27 10:17 ` Peter Zijlstra
2021-07-27 1:07 ` Guo Ren
2021-07-27 1:52 ` Wang Rui
2021-07-27 11:03 ` Peter Zijlstra
2021-07-27 2:00 ` Boqun Feng
2021-07-27 10:50 ` Peter Zijlstra
2021-07-27 10:12 ` Peter Zijlstra
2021-07-26 9:00 ` Arnd Bergmann
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