From: Stafford Horne <shorne@gmail.com>
To: Peter Zijlstra <peterz@infradead.org>
Cc: "Guo Ren" <guoren@kernel.org>,
"Christoph Müllner" <christophm30@gmail.com>,
"Palmer Dabbelt" <palmer@dabbelt.com>,
"Anup Patel" <anup@brainfault.org>,
linux-riscv <linux-riscv@lists.infradead.org>,
"Linux Kernel Mailing List" <linux-kernel@vger.kernel.org>,
"Guo Ren" <guoren@linux.alibaba.com>,
"Catalin Marinas" <catalin.marinas@arm.com>,
"Will Deacon" <will.deacon@arm.com>,
"Arnd Bergmann" <arnd@arndb.de>,
jonas@southpole.se, stefan.kristiansson@saunalahti.fi
Subject: Re: [RFC][PATCH] locking: Generic ticket-lock
Date: Thu, 15 Apr 2021 06:02:49 +0900 [thread overview]
Message-ID: <20210414210249.GK3288043@lianli.shorne-pla.net> (raw)
In-Reply-To: <YHbj987Ks0JOKw/X@hirez.programming.kicks-ass.net>
On Wed, Apr 14, 2021 at 02:45:43PM +0200, Peter Zijlstra wrote:
> On Wed, Apr 14, 2021 at 12:16:38PM +0200, Peter Zijlstra wrote:
> > On Wed, Apr 14, 2021 at 11:05:24AM +0200, Peter Zijlstra wrote:
> >
> > > That made me look at the qspinlock code, and queued_spin_*lock() uses
> > > atomic_try_cmpxchg_acquire(), which means any arch that uses qspinlock
> > > and has RCpc atomics will give us massive pain.
> > >
> > > Current archs using qspinlock are: x86, arm64, power, sparc64, mips and
> > > openrisc (WTF?!).
> > >
> > > Of those, x86 and sparc are TSO archs with SC atomics, arm64 has RCsc
> > > atomics, power has RCtso atomics (and is the arch we all hate for having
> > > RCtso locks).
> > >
> > > Now MIPS has all sorts of ill specified barriers, but last time looked
> > > at it it didn't actually use any of that and stuck to using smp_mb(), so
> > > it will have RCsc atomics.
> > >
> > > /me goes look at wth openrisc is.. doesn't even appear to have
> > > asm/barrier.h :-/ Looking at wikipedia it also doesn't appear to
> > > actually have hardware ...
> >
> > FWIW this is broken, anything SMP *MUST* define mb(), at the very least.
>
> As near as I can tell this should do. The arch spec only lists this one
> instruction and the text makes it sound like a completion barrier.
Yes, I will submit this patch.
The l.msync instruction completes all load/store operations.
The l.lwa/l.swa pair (used for xchg/cmpxchg) also implies l.msync.
> ---
> arch/openrisc/include/asm/barrier.h | 9 +++++++++
> 1 file changed, 9 insertions(+)
>
> diff --git a/arch/openrisc/include/asm/barrier.h b/arch/openrisc/include/asm/barrier.h
> new file mode 100644
> index 000000000000..7538294721be
> --- /dev/null
> +++ b/arch/openrisc/include/asm/barrier.h
> @@ -0,0 +1,9 @@
> +/* SPDX-License-Identifier: GPL-2.0 */
> +#ifndef __ASM_BARRIER_H
> +#define __ASM_BARRIER_H
> +
> +#define mb() asm volatile ("l.msync" ::: "memory")
> +
> +#include <asm-generic/barrier.h>
> +
> +#endif /* __ASM_BARRIER_H */
_______________________________________________
linux-riscv mailing list
linux-riscv@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-riscv
next prev parent reply other threads:[~2021-04-14 21:04 UTC|newest]
Thread overview: 46+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-03-24 10:14 [PATCH] riscv: locks: introduce ticket-based spinlock implementation guoren
2021-03-24 11:09 ` Peter Zijlstra
2021-03-24 12:10 ` Guo Ren
[not found] ` <CAM4kBBK7_s9U2vJbq68yC8WdDEfPQTaCOvn1xds3Si5B-Wpw+A@mail.gmail.com>
2021-03-24 12:23 ` Peter Zijlstra
2021-03-24 12:24 ` Guo Ren
2021-03-24 12:31 ` Peter Zijlstra
2021-03-24 12:28 ` Anup Patel
2021-03-24 12:37 ` Peter Zijlstra
2021-03-24 12:53 ` Anup Patel
2021-04-11 21:11 ` Palmer Dabbelt
2021-04-12 13:32 ` Christoph Müllner
2021-04-12 14:51 ` Peter Zijlstra
2021-04-12 21:21 ` Christoph Müllner
2021-04-12 17:33 ` Palmer Dabbelt
2021-04-12 21:54 ` Christoph Müllner
2021-04-13 8:03 ` Peter Zijlstra
2021-04-13 8:17 ` Peter Zijlstra
2021-04-14 2:26 ` Guo Ren
2021-04-14 7:08 ` Peter Zijlstra
2021-04-14 9:05 ` Peter Zijlstra
2021-04-14 10:16 ` [RFC][PATCH] locking: Generic ticket-lock Peter Zijlstra
2021-04-14 12:39 ` Guo Ren
2021-04-14 12:55 ` Peter Zijlstra
2021-04-14 13:08 ` Peter Zijlstra
2021-04-14 15:59 ` David Laight
2021-04-14 12:45 ` Peter Zijlstra
2021-04-14 21:02 ` Stafford Horne [this message]
2021-04-14 20:47 ` Stafford Horne
2021-04-15 8:09 ` Peter Zijlstra
2021-04-15 9:02 ` Catalin Marinas
2021-04-15 9:22 ` Will Deacon
2021-04-15 9:24 ` Peter Zijlstra
2021-04-19 17:35 ` Will Deacon
2021-04-23 6:44 ` Palmer Dabbelt
2021-04-13 9:22 ` [PATCH] riscv: locks: introduce ticket-based spinlock implementation Christoph Müllner
2021-04-13 9:30 ` Catalin Marinas
2021-04-13 9:55 ` Christoph Müllner
2021-04-14 0:23 ` Guo Ren
2021-04-14 9:17 ` Catalin Marinas
2021-04-13 9:35 ` Peter Zijlstra
2021-04-13 10:25 ` Christoph Müllner
2021-04-13 10:45 ` Catalin Marinas
2021-04-13 10:54 ` David Laight
2021-04-14 5:54 ` Guo Ren
2021-04-13 11:04 ` Christoph Müllner
2021-04-13 13:19 ` Guo Ren
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=20210414210249.GK3288043@lianli.shorne-pla.net \
--to=shorne@gmail.com \
--cc=anup@brainfault.org \
--cc=arnd@arndb.de \
--cc=catalin.marinas@arm.com \
--cc=christophm30@gmail.com \
--cc=guoren@kernel.org \
--cc=guoren@linux.alibaba.com \
--cc=jonas@southpole.se \
--cc=linux-kernel@vger.kernel.org \
--cc=linux-riscv@lists.infradead.org \
--cc=palmer@dabbelt.com \
--cc=peterz@infradead.org \
--cc=stefan.kristiansson@saunalahti.fi \
--cc=will.deacon@arm.com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).