From: "Arnd Bergmann" <arnd@arndb.de>
To: "D. Jeff Dionne" <djeffdionne@gmail.com>,
"Paul E. McKenney" <paulmck@kernel.org>
Cc: "John Paul Adrian Glaubitz" <glaubitz@physik.fu-berlin.de>,
Linux-Arch <linux-arch@vger.kernel.org>,
linux-kernel@vger.kernel.org, "Marco Elver" <elver@google.com>,
"Andrew Morton" <akpm@linux-foundation.org>,
"Thomas Gleixner" <tglx@linutronix.de>,
"Peter Zijlstra" <peterz@infradead.org>,
"Doug Anderson" <dianders@chromium.org>,
"Petr Mladek" <pmladek@suse.com>,
"Linus Torvalds" <torvalds@linux-foundation.org>,
kernel-team@meta.com, "Andi Shyti" <andi.shyti@linux.intel.com>,
"Palmer Dabbelt" <palmer@rivosinc.com>,
"Masami Hiramatsu" <mhiramat@kernel.org>,
linux-sh@vger.kernel.org
Subject: Re: [PATCH v2 cmpxchg 12/13] sh: Emulate one-byte cmpxchg
Date: Thu, 02 May 2024 13:30:58 +0200 [thread overview]
Message-ID: <31ed4654-094a-4e1e-9182-973b43ae3464@app.fastmail.com> (raw)
In-Reply-To: <23A87C03-EB55-49A1-BB55-B6136117F0B6@gmail.com>
On Thu, May 2, 2024, at 07:42, D. Jeff Dionne wrote:
> On May 2, 2024, at 14:07, Paul E. McKenney <paulmck@kernel.org> wrote:
>
>> That would be 8-bit xchg() rather than 8-byte cmpxchg(), correct?
>>
>> Or am I missing something subtle here that makes sh also support one-byte
>> (8-bit) cmpxchg()?
>
> The native SH atomic operation is test and set TAS.B. J2 adds a
> compare and swap CAS.L instruction, carefully chosen for patent free
> prior art (s360, IIRC).
>
> The (relatively expensive) encoding space we allocated for CAS.L does
> not contain size bits.
>
> Not all SH4 patents had expired when J2 was under development, but now
> have (watch this space). Not sure (me myself) if there are more atomic
> operations in sh4.
SH4A supports MIPS R4000 style LL/SC instructions, but it looks like
the older SH4 does not.
Arnd
prev parent reply other threads:[~2024-05-02 11:31 UTC|newest]
Thread overview: 18+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <b67e79d4-06cb-4a45-a906-b9e0fbae22c5@paulmck-laptop>
2024-05-01 23:01 ` [PATCH v2 cmpxchg 12/13] sh: Emulate one-byte cmpxchg Paul E. McKenney
2024-05-02 4:52 ` John Paul Adrian Glaubitz
2024-05-02 5:06 ` Paul E. McKenney
2024-05-02 5:11 ` John Paul Adrian Glaubitz
2024-05-02 13:33 ` Paul E. McKenney
2024-05-02 20:53 ` Al Viro
2024-05-02 21:01 ` alpha cmpxchg.h (was Re: [PATCH v2 cmpxchg 12/13] sh: Emulate one-byte cmpxchg) Al Viro
2024-05-02 22:16 ` Linus Torvalds
2024-05-02 21:18 ` [PATCH v2 cmpxchg 12/13] sh: Emulate one-byte cmpxchg Paul E. McKenney
2024-05-02 22:07 ` Al Viro
2024-05-02 23:12 ` Paul E. McKenney
2024-05-02 23:24 ` Al Viro
2024-05-02 23:45 ` Paul E. McKenney
2024-05-02 23:32 ` Linus Torvalds
2024-05-03 0:16 ` Paul E. McKenney
2024-05-02 21:50 ` Arnd Bergmann
2024-05-02 5:42 ` D. Jeff Dionne
2024-05-02 11:30 ` Arnd Bergmann [this message]
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