From: Peter Zijlstra <peterz@infradead.org>
To: Andrea Parri <andrea.parri@amarulasolutions.com>
Cc: Will Deacon <will.deacon@arm.com>,
Mark Rutland <mark.rutland@arm.com>,
linux-kernel@vger.kernel.org, aou@eecs.berkeley.edu,
arnd@arndb.de, bp@alien8.de, catalin.marinas@arm.com,
davem@davemloft.net, fenghua.yu@intel.com,
heiko.carstens@de.ibm.com, herbert@gondor.apana.org.au,
ink@jurassic.park.msu.ru, jhogan@kernel.org,
linux@armlinux.org.uk, mattst88@gmail.com, mingo@kernel.org,
mpe@ellerman.id.au, palmer@sifive.com, paul.burton@mips.com,
paulus@samba.org, ralf@linux-mips.org, rth@twiddle.net,
stable@vger.kernel.org, tglx@linutronix.de, tony.luck@intel.com,
vgupta@synopsys.com, gregkh@linuxfoundation.org,
jhansen@vmware.com, vdasa@vmware.com, aditr@vmware.com,
Steven Rostedt <rostedt@goodmis.org>
Subject: Re: [PATCH 00/18] locking/atomic: atomic64 type cleanup
Date: Tue, 28 May 2019 12:47:19 +0200 [thread overview]
Message-ID: <20190528104719.GN2623@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <20190524224340.GA3792@andrea>
On Sat, May 25, 2019 at 12:43:40AM +0200, Andrea Parri wrote:
> > ---
> > Subject: Documentation/atomic_t.txt: Clarify pure non-rmw usage
> >
> > Clarify that pure non-RMW usage of atomic_t is pointless, there is
> > nothing 'magical' about atomic_set() / atomic_read().
> >
> > This is something that seems to confuse people, because I happen upon it
> > semi-regularly.
> >
> > Acked-by: Will Deacon <will.deacon@arm.com>
> > Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
> > Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
> > ---
> > Documentation/atomic_t.txt | 6 ++++--
> > 1 file changed, 4 insertions(+), 2 deletions(-)
> >
> > diff --git a/Documentation/atomic_t.txt b/Documentation/atomic_t.txt
> > index dca3fb0554db..89eae7f6b360 100644
> > --- a/Documentation/atomic_t.txt
> > +++ b/Documentation/atomic_t.txt
> > @@ -81,9 +81,11 @@ SEMANTICS
> >
> > The non-RMW ops are (typically) regular LOADs and STOREs and are canonically
> > implemented using READ_ONCE(), WRITE_ONCE(), smp_load_acquire() and
> > -smp_store_release() respectively.
> > +smp_store_release() respectively. Therefore, if you find yourself only using
> > +the Non-RMW operations of atomic_t, you do not in fact need atomic_t at all
> > +and are doing it wrong.
>
> The counterargument (not so theoretic, just look around in the kernel!) is:
> we all 'forget' to use READ_ONCE() and WRITE_ONCE(), it should be difficult
> or more difficult to forget to use atomic_read() and atomic_set()... IAC,
> I wouldn't call any of them 'wrong'.
I'm thinking you mean that the type system isn't helping us with
READ/WRITE_ONCE() like it does with atomic_t ? And while I agree that
there is room for improvement there, that doesn't mean we should start
using atomic*_t all over the place for that.
Part of the problem with READ/WRITE_ONCE() is that it serves a dual
purpose; we've tried to untangle that at some point, but Linus wasn't
having it.
next prev parent reply other threads:[~2019-05-28 10:48 UTC|newest]
Thread overview: 60+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-05-22 13:22 [PATCH 00/18] locking/atomic: atomic64 type cleanup Mark Rutland
2019-05-22 13:22 ` [PATCH 01/18] locking/atomic: crypto: nx: prepare for atomic64_read() conversion Mark Rutland
2019-06-03 13:34 ` [tip:locking/core] locking/atomic, crypto/nx: Prepare " tip-bot for Mark Rutland
2019-05-22 13:22 ` [PATCH 02/18] locking/atomic: s390/pci: prepare " Mark Rutland
2019-06-03 13:34 ` [tip:locking/core] locking/atomic, s390/pci: Prepare " tip-bot for Mark Rutland
2019-05-22 13:22 ` [PATCH 03/18] locking/atomic: generic: use s64 for atomic64 Mark Rutland
2019-05-22 21:16 ` Arnd Bergmann
2019-06-03 13:35 ` [tip:locking/core] locking/atomic: Use " tip-bot for Mark Rutland
2019-05-22 13:22 ` [PATCH 04/18] locking/atomic: alpha: use " Mark Rutland
2019-06-03 13:36 ` [tip:locking/core] locking/atomic, alpha: Use " tip-bot for Mark Rutland
2019-05-22 13:22 ` [PATCH 05/18] locking/atomic: arc: use " Mark Rutland
2019-05-23 23:10 ` Vineet Gupta
2019-06-03 13:36 ` [tip:locking/core] locking/atomic, arc: Use " tip-bot for Mark Rutland
2019-05-22 13:22 ` [PATCH 06/18] locking/atomic: arm: use " Mark Rutland
2019-06-03 13:37 ` [tip:locking/core] locking/atomic, arm: Use " tip-bot for Mark Rutland
2019-05-22 13:22 ` [PATCH 07/18] locking/atomic: arm64: use " Mark Rutland
2019-06-03 13:38 ` [tip:locking/core] locking/atomic, arm64: Use " tip-bot for Mark Rutland
2019-05-22 13:22 ` [PATCH 08/18] locking/atomic: ia64: use " Mark Rutland
2019-06-03 13:39 ` [tip:locking/core] locking/atomic, ia64: Use " tip-bot for Mark Rutland
2019-05-22 13:22 ` [PATCH 09/18] locking/atomic: mips: use " Mark Rutland
2019-06-03 13:39 ` [tip:locking/core] locking/atomic, mips: Use " tip-bot for Mark Rutland
2019-05-22 13:22 ` [PATCH 10/18] locking/atomic: powerpc: use " Mark Rutland
2019-05-23 13:27 ` Michael Ellerman
2019-06-03 13:40 ` [tip:locking/core] locking/atomic, powerpc: Use " tip-bot for Mark Rutland
2019-05-22 13:22 ` [PATCH 11/18] locking/atomic: riscv: fix atomic64_sub_if_positive() offset argument Mark Rutland
2019-05-22 19:06 ` Palmer Dabbelt
2019-06-03 13:41 ` [tip:locking/core] locking/atomic, riscv: Fix " tip-bot for Mark Rutland
2019-05-22 13:22 ` [PATCH 12/18] locking/atomic: riscv: use s64 for atomic64 Mark Rutland
2019-05-22 19:06 ` Palmer Dabbelt
2019-05-23 10:23 ` Mark Rutland
2019-06-03 13:41 ` [tip:locking/core] locking/atomic, riscv: Use " tip-bot for Mark Rutland
2019-05-22 13:22 ` [PATCH 13/18] locking/atomic: s390: use " Mark Rutland
2019-06-03 13:42 ` [tip:locking/core] locking/atomic, s390: Use " tip-bot for Mark Rutland
2019-05-22 13:22 ` [PATCH 14/18] locking/atomic: sparc: use " Mark Rutland
2019-06-03 13:43 ` [tip:locking/core] locking/atomic, sparc: Use " tip-bot for Mark Rutland
2019-05-22 13:22 ` [PATCH 15/18] locking/atomic: x86: use " Mark Rutland
2019-06-03 13:44 ` [tip:locking/core] locking/atomic, x86: Use " tip-bot for Mark Rutland
2019-05-22 13:22 ` [PATCH 16/18] locking/atomic: use s64 for atomic64_t on 64-bit Mark Rutland
2019-06-03 13:44 ` [tip:locking/core] locking/atomic: Use " tip-bot for Mark Rutland
2019-05-22 13:22 ` [PATCH 17/18] locking/atomic: crypto: nx: remove redundant casts Mark Rutland
2019-06-03 13:45 ` [tip:locking/core] locking/atomic, crypto/nx: Remove " tip-bot for Mark Rutland
2019-05-22 13:22 ` [PATCH 18/18] locking/atomic: s390/pci: remove " Mark Rutland
2019-06-03 13:46 ` [tip:locking/core] locking/atomic, s390/pci: Remove " tip-bot for Mark Rutland
2019-05-22 21:18 ` [PATCH 00/18] locking/atomic: atomic64 type cleanup Arnd Bergmann
2019-05-23 10:28 ` Mark Rutland
2019-05-23 8:30 ` Andrea Parri
2019-05-23 10:19 ` Mark Rutland
2019-05-23 11:20 ` Andrea Parri
2019-05-24 10:37 ` Peter Zijlstra
2019-05-24 11:18 ` Peter Zijlstra
2019-05-24 11:38 ` Greg KH
2019-05-24 11:42 ` Will Deacon
2019-05-24 11:52 ` Peter Zijlstra
2019-05-24 22:43 ` Andrea Parri
2019-05-28 10:47 ` Peter Zijlstra [this message]
2019-05-28 11:15 ` Andrea Parri
2019-06-03 13:46 ` [tip:locking/core] Documentation/atomic_t.txt: Clarify pure non-rmw usage tip-bot for Peter Zijlstra
2019-06-06 8:44 ` Andrea Parri
2019-06-06 9:04 ` Peter Zijlstra
2019-06-06 9:11 ` Andrea Parri
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