From: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
To: Christophe Leroy <christophe.leroy@csgroup.eu>
Cc: Ingo Molnar <mingo@redhat.com>,
Peter Zijlstra <peterz@infradead.org>,
Thomas Gleixner <tglx@linutronix.de>,
maged michael <maged.michael@gmail.com>,
Dave Watson <davejwatson@fb.com>,
Will Deacon <will.deacon@arm.com>,
"Russell King, ARM Linux" <linux@armlinux.org.uk>,
David Sehr <sehr@google.com>, Paul Mackerras <paulus@samba.org>,
"H. Peter Anvin" <hpa@zytor.com>,
linux-arch <linux-arch@vger.kernel.org>, x86 <x86@kernel.org>,
Andrew Hunter <ahh@google.com>,
Greg Hackmann <ghackmann@google.com>,
Alan Stern <stern@rowland.harvard.edu>,
Paul <paulmck@linux.vnet.ibm.com>,
Andrea Parri <parri.andrea@gmail.com>,
Avi Kivity <avi@scylladb.com>, Boqun Feng <boqun.feng@gmail.com>,
linuxppc-dev <linuxppc-dev@lists.ozlabs.org>,
Nicholas Piggin <npiggin@gmail.com>,
Alexander Viro <viro@zeniv.linux.org.uk>,
Andy Lutomirski <luto@kernel.org>,
linux-api <linux-api@vger.kernel.org>,
linux-kernel <linux-kernel@vger.kernel.org>,
Linus Torvalds <torvalds@linux-foundation.org>
Subject: Re: [PATCH for 4.16 v7 02/11] powerpc: membarrier: Skip memory barrier in switch_mm()
Date: Fri, 18 Jun 2021 13:26:32 -0400 (EDT) [thread overview]
Message-ID: <2077369633.12794.1624037192994.JavaMail.zimbra@efficios.com> (raw)
In-Reply-To: <8b200dd5-f37b-b208-82fb-2775df7bcd49@csgroup.eu>
----- On Jun 18, 2021, at 1:13 PM, Christophe Leroy christophe.leroy@csgroup.eu wrote:
[...]
>
> I don't understand all that complexity to just replace a simple
> 'smp_mb__after_unlock_lock()'.
>
> #define smp_mb__after_unlock_lock() smp_mb()
> #define smp_mb() barrier()
> # define barrier() __asm__ __volatile__("": : :"memory")
>
>
> Am I missing some subtility ?
On powerpc CONFIG_SMP, smp_mb() is actually defined as:
#define smp_mb() __smp_mb()
#define __smp_mb() mb()
#define mb() __asm__ __volatile__ ("sync" : : : "memory")
So the original motivation here was to skip a "sync" instruction whenever
switching between threads which are part of the same process. But based on
recent discussions, I suspect my implementation may be inaccurately doing
so though.
Thanks,
Mathieu
>
> Thanks
> Christophe
--
Mathieu Desnoyers
EfficiOS Inc.
http://www.efficios.com
next prev parent reply other threads:[~2021-06-18 17:26 UTC|newest]
Thread overview: 21+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-01-29 20:20 [PATCH for 4.16 00/11] membarrier updates for 4.16 Mathieu Desnoyers
2018-01-29 20:20 ` [PATCH for 4.16 v2 01/11] membarrier: selftest: Test private expedited cmd Mathieu Desnoyers
2018-01-29 20:20 ` [PATCH for 4.16 v7 02/11] powerpc: membarrier: Skip memory barrier in switch_mm() Mathieu Desnoyers
2018-02-05 20:22 ` Ingo Molnar
[not found] ` <20180205202242.6ilyjh35byycf3ez-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
2018-02-05 20:32 ` Mathieu Desnoyers
2021-06-18 17:13 ` Christophe Leroy
2021-06-18 17:26 ` Mathieu Desnoyers [this message]
2021-06-19 9:35 ` Christophe Leroy
2021-06-19 15:02 ` Segher Boessenkool
2021-06-21 14:11 ` Christophe Leroy
2021-06-22 0:15 ` Segher Boessenkool
2018-01-29 20:20 ` [PATCH for 4.16 v5 03/11] membarrier: Document scheduler barrier requirements Mathieu Desnoyers
2018-01-29 20:20 ` [PATCH for 4.16 v2 05/11] membarrier: selftest: Test global expedited cmd Mathieu Desnoyers
2018-01-29 20:20 ` [PATCH for 4.16 v2 06/11] Introduce sync_core_before_usermode Mathieu Desnoyers
2018-01-29 20:20 ` [PATCH for 4.16 v3 07/11] x86: Implement sync_core_before_usermode Mathieu Desnoyers
2018-01-29 20:20 ` [PATCH for 4.16 v4 09/11] membarrier: x86: Provide core serializing command Mathieu Desnoyers
2018-01-29 20:20 ` [PATCH for 4.16 10/11] membarrier: arm64: " Mathieu Desnoyers
[not found] ` <20180129202020.8515-1-mathieu.desnoyers-vg+e7yoeK/dWk0Htik3J/w@public.gmane.org>
2018-01-29 20:20 ` [PATCH for 4.16 v3 04/11] membarrier: provide GLOBAL_EXPEDITED command Mathieu Desnoyers
2018-01-29 20:20 ` [PATCH for 4.16 v3 08/11] membarrier: Provide core serializing command Mathieu Desnoyers
2018-01-29 20:20 ` [PATCH for 4.16 11/11] membarrier: selftest: Test private expedited sync core cmd Mathieu Desnoyers
2018-02-05 21:21 ` [PATCH for 4.16 00/11] membarrier updates for 4.16 Ingo Molnar
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