From: Peter Zijlstra <peterz@infradead.org>
To: Will Deacon <will.deacon@arm.com>
Cc: Mark Rutland <mark.rutland@arm.com>,
Andrea Parri <andrea.parri@amarulasolutions.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: Fri, 24 May 2019 13:52:31 +0200 [thread overview]
Message-ID: <20190524115231.GN2623@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <20190524114220.GA4260@fuggles.cambridge.arm.com>
On Fri, May 24, 2019 at 12:42:20PM +0100, Will Deacon wrote:
> > diff --git a/Documentation/atomic_t.txt b/Documentation/atomic_t.txt
> > index dca3fb0554db..125c95ddbbc0 100644
> > --- a/Documentation/atomic_t.txt
> > +++ b/Documentation/atomic_t.txt
> > @@ -83,6 +83,9 @@ 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.
> >
>
> Not sure you need a new paragraph here.
>
> > +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.
> > +
>
> That makes sense to me, although I now find that the sentence below is a bit
> confusing because it sounds like it's a caveat relating to only using
> Non-RMW ops.
>
> > The one detail to this is that atomic_set{}() should be observable to the RMW
> > ops. That is:
>
> How about changing this to be:
>
> "A subtle detail of atomic_set{}() is that it should be observable..."
Done, find below.
---
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 one detail to this is that atomic_set{}() should be observable to the RMW
+A subtle detail of atomic_set{}() is that it should be observable to the RMW
ops. That is:
C atomic-set
next prev parent reply other threads:[~2019-05-24 11:54 UTC|newest]
Thread overview: 38+ 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
2019-05-22 13:22 ` [PATCH 02/18] locking/atomic: s390/pci: " 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
2019-05-22 13:22 ` [PATCH 04/18] locking/atomic: alpha: " Mark Rutland
2019-05-22 13:22 ` [PATCH 05/18] locking/atomic: arc: " Mark Rutland
2019-05-23 23:10 ` Vineet Gupta
2019-05-22 13:22 ` [PATCH 06/18] locking/atomic: arm: " Mark Rutland
2019-05-22 13:22 ` [PATCH 07/18] locking/atomic: arm64: " Mark Rutland
2019-05-22 13:22 ` [PATCH 08/18] locking/atomic: ia64: " Mark Rutland
2019-05-22 13:22 ` [PATCH 09/18] locking/atomic: mips: " Mark Rutland
2019-05-22 13:22 ` [PATCH 10/18] locking/atomic: powerpc: " Mark Rutland
2019-05-23 13:27 ` Michael Ellerman
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
2019-05-22 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
2019-05-22 13:22 ` [PATCH 13/18] locking/atomic: s390: " Mark Rutland
2019-05-22 13:22 ` [PATCH 14/18] locking/atomic: sparc: " Mark Rutland
2019-05-22 13:22 ` [PATCH 15/18] locking/atomic: x86: " Mark Rutland
2019-05-22 13:22 ` [PATCH 16/18] locking/atomic: use s64 for atomic64_t on 64-bit Mark Rutland
2019-05-22 13:22 ` [PATCH 17/18] locking/atomic: crypto: nx: remove redundant casts Mark Rutland
2019-05-22 13:22 ` [PATCH 18/18] locking/atomic: s390/pci: " 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 [this message]
2019-05-24 22:43 ` Andrea Parri
2019-05-28 10:47 ` Peter Zijlstra
2019-05-28 11:15 ` Andrea Parri
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