From: David Laight <David.Laight@ACULAB.COM>
To: 'Linus Torvalds' <torvalds@linux-foundation.org>,
Steven Rostedt <rostedt@goodmis.org>
Cc: "linux-arch@vger.kernel.org" <linux-arch@vger.kernel.org>,
LKML <linux-kernel@vger.kernel.org>,
Linux Trace Kernel <linux-trace-kernel@vger.kernel.org>,
Masami Hiramatsu <mhiramat@kernel.org>,
Mark Rutland <mark.rutland@arm.com>,
Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Subject: RE: [PATCH] ring-buffer: Remove 32bit timestamp logic
Date: Sun, 17 Dec 2023 17:40:19 +0000 [thread overview]
Message-ID: <d3e5ab37839047a483212c8b3fc667e5@AcuMS.aculab.com> (raw)
In-Reply-To: <CAHk-=wieVSfyjTpe8L5kmwC4mk9dRge9dvyJiMZEkyz4-tOvow@mail.gmail.com>
...
> My guess is that *most* 32-bit architectures do not have a 64-bit
> cmpxchg - not even the irq-safe one.
Does any sparc32 even have a 32-bit cmpxchg?
The original versions (which were definitely SMP capable)
only had a byte sized atomic exchange that always wrote 0xff.
Sparc32 does have 'load/store double' (two 32bit registers)
but 32bit cpu like nios2 and (I think) RISCV (and probably
anything else loosely based on MIPS) only have single register
load/store instructions.
They'll mainly be UP only, I've not looked at RISCV enough to
see what it has when supporting SMP.
> For the UP case you can do your own, of course.
A generic version of the soft interrupt disable code would help.
Then it would just be an inc/dec of memory rather than having
to save the current interrupt enable state.
Especially for code that only disables interrupts for a few
instructions - so the costs of deferring the interrupt don't
happen often.
David
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Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK
Registration No: 1397386 (Wales)
prev parent reply other threads:[~2023-12-17 17:40 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <20231213211126.24f8c1dd@gandalf.local.home>
2023-12-14 2:46 ` [PATCH] ring-buffer: Remove 32bit timestamp logic Steven Rostedt
2023-12-14 6:53 ` Linus Torvalds
2023-12-14 16:56 ` Steven Rostedt
2023-12-14 19:44 ` Linus Torvalds
2023-12-14 20:36 ` Steven Rostedt
2023-12-14 20:50 ` Linus Torvalds
2023-12-14 21:01 ` Steven Rostedt
2023-12-17 17:40 ` David Laight [this message]
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