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From: Olivier Dion via lttng-dev <lttng-dev@lists.lttng.org>
To: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>, paulmck@kernel.org
Cc: lttng-dev@lists.lttng.org
Subject: Re: [lttng-dev] [PATCH 02/11] urcu/uatomic: Use atomic builtins if configured
Date: Thu, 22 Jun 2023 16:10:57 -0400	[thread overview]
Message-ID: <87v8ffl0ku.fsf@laura> (raw)
In-Reply-To: <9e5fbcf0-bf3d-c0b3-c45b-2e440e8276e1@efficios.com>

On Thu, 22 Jun 2023, Mathieu Desnoyers <mathieu.desnoyers@efficios.com> wrote:
> On 6/22/23 15:53, Olivier Dion wrote:
>> On Thu, 22 Jun 2023, "Paul E. McKenney" <paulmck@kernel.org> wrote:
>> 
>>> I suggest C11 volatile atomic load/store.  Load/store fusing is permitted
>>> for non-volatile atomic loads and stores, and such fusing can ruin your
>>> code's entire day.  ;-)
>> 
>> Good catch.  Seems like not a problem on GCC (yet), but Clang is extremely
>> aggressive and seems to do store fusing on some corner cases [0].
>
> I don't think this is an example of store fusing, but rather just that 
> the compiler can eliminate stores to static variables which are 
> otherwise unused, making the entire variable useless.

Indeed, that is not store fusing.  It is however interesting to see that
the dead store elimination is avoid when casting one of the &x with a
volatile qualifier.  TIL dead store can apply to atomics.

-- 
Olivier Dion
EfficiOS Inc.
https://www.efficios.com
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  reply	other threads:[~2023-06-22 20:11 UTC|newest]

Thread overview: 69+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2023-05-15 20:17 [lttng-dev] [PATCH 00/11] Add support for TSAN to liburcu Olivier Dion via lttng-dev
2023-05-15 20:17 ` [lttng-dev] [PATCH 01/11] configure: Add --disable-atomic-builtins option Olivier Dion via lttng-dev
2023-05-15 20:17 ` [lttng-dev] [PATCH 02/11] urcu/uatomic: Use atomic builtins if configured Olivier Dion via lttng-dev
2023-06-21 23:19   ` Paul E. McKenney via lttng-dev
2023-06-22 15:55     ` Mathieu Desnoyers via lttng-dev
2023-06-22 18:32       ` Paul E. McKenney via lttng-dev
2023-06-22 19:53         ` Olivier Dion via lttng-dev
2023-06-22 19:56           ` Mathieu Desnoyers via lttng-dev
2023-06-22 20:10             ` Olivier Dion via lttng-dev [this message]
2023-06-22 20:11           ` Paul E. McKenney via lttng-dev
2023-06-22 19:54         ` Mathieu Desnoyers via lttng-dev
2023-06-29 17:22         ` Olivier Dion via lttng-dev
2023-06-29 17:27           ` Olivier Dion via lttng-dev
2023-06-29 18:33             ` Mathieu Desnoyers via lttng-dev
2023-06-29 18:29           ` Mathieu Desnoyers via lttng-dev
2023-05-15 20:17 ` [lttng-dev] [PATCH 03/11] urcu/compiler: " Olivier Dion via lttng-dev
2023-05-15 20:17 ` [lttng-dev] [PATCH 04/11] urcu/arch/generic: " Olivier Dion via lttng-dev
2023-06-21 23:22   ` Paul E. McKenney via lttng-dev
2023-06-22  0:53     ` Olivier Dion via lttng-dev
2023-06-22  1:48       ` Mathieu Desnoyers via lttng-dev
2023-06-22  3:44         ` Paul E. McKenney via lttng-dev
2023-05-15 20:17 ` [lttng-dev] [PATCH 05/11] urcu/system: " Olivier Dion via lttng-dev
2023-05-15 20:17 ` [lttng-dev] [PATCH 06/11] urcu/uatomic: Add CMM memory model Olivier Dion via lttng-dev
2023-05-15 20:17 ` [lttng-dev] [PATCH 07/11] urcu-wait: Fix wait state load/store Olivier Dion via lttng-dev
2023-05-15 20:17 ` [lttng-dev] [PATCH 08/11] tests: Use uatomic for accessing global states Olivier Dion via lttng-dev
2023-05-15 20:17 ` [lttng-dev] [PATCH 09/11] benchmark: " Olivier Dion via lttng-dev
2023-05-15 20:17 ` [lttng-dev] [PATCH 10/11] tests/unit/test_build: Quiet unused return value Olivier Dion via lttng-dev
2023-05-15 20:17 ` [lttng-dev] [PATCH 11/11] urcu/annotate: Add CMM annotation Olivier Dion via lttng-dev
2023-05-16 15:57   ` Olivier Dion via lttng-dev
2023-05-16  8:18 ` [lttng-dev] [PATCH 00/11] Add support for TSAN to liburcu Dmitry Vyukov via lttng-dev
2023-05-16 15:47   ` Olivier Dion via lttng-dev
2023-05-17 10:21     ` Dmitry Vyukov via lttng-dev
2023-05-17 10:57       ` Dmitry Vyukov via lttng-dev
2023-05-17 14:44         ` Olivier Dion via lttng-dev
2023-05-23 16:05           ` Olivier Dion via lttng-dev
2023-05-24  8:14             ` Dmitry Vyukov via lttng-dev
2023-05-26  5:33               ` Ondřej Surý via lttng-dev
2023-05-26  6:08                 ` Dmitry Vyukov via lttng-dev
2023-05-26  6:10                   ` Dmitry Vyukov via lttng-dev
2023-05-26 10:06                   ` Ondřej Surý via lttng-dev
2023-05-26 10:08                     ` Dmitry Vyukov via lttng-dev
2023-05-26 14:20                     ` Olivier Dion via lttng-dev
2023-05-26 15:15               ` Olivier Dion via lttng-dev
2023-05-17 14:44       ` Olivier Dion via lttng-dev
2023-06-07 18:53 ` [lttng-dev] [PATCH v2 00/12] " Olivier Dion via lttng-dev
2023-06-07 19:04   ` Ondřej Surý via lttng-dev
2023-06-07 19:20     ` Olivier Dion via lttng-dev
2023-06-07 18:53 ` [lttng-dev] [PATCH v2 01/12] configure: Add --disable-atomic-builtins option Olivier Dion via lttng-dev
2023-06-07 18:53 ` [lttng-dev] [PATCH v2 02/12] urcu/compiler: Use atomic builtins if configured Olivier Dion via lttng-dev
2023-06-07 18:53 ` [lttng-dev] [PATCH v2 03/12] urcu/arch/generic: " Olivier Dion via lttng-dev
2023-06-07 18:53 ` [lttng-dev] [PATCH v2 04/12] urcu/system: " Olivier Dion via lttng-dev
2023-06-21 23:23   ` Paul E. McKenney via lttng-dev
2023-07-04 14:43     ` Olivier Dion via lttng-dev
2023-07-05 18:48       ` Paul E. McKenney via lttng-dev
2023-07-05 19:03         ` Olivier Dion via lttng-dev
2023-07-05 19:28           ` Paul E. McKenney via lttng-dev
2023-06-07 18:53 ` [lttng-dev] [PATCH v2 05/12] urcu/uatomic: Add CMM memory model Olivier Dion via lttng-dev
2023-06-21 23:28   ` Paul E. McKenney via lttng-dev
2023-06-29 16:49     ` Olivier Dion via lttng-dev
2023-06-29 18:40       ` Paul E. McKenney via lttng-dev
2023-06-07 18:53 ` [lttng-dev] [PATCH v2 06/12] urcu-wait: Fix wait state load/store Olivier Dion via lttng-dev
2023-06-07 18:53 ` [lttng-dev] [PATCH v2 07/12] tests: Use uatomic for accessing global states Olivier Dion via lttng-dev
2023-06-21 23:37   ` Paul E. McKenney via lttng-dev
2023-06-07 18:53 ` [lttng-dev] [PATCH v2 08/12] benchmark: " Olivier Dion via lttng-dev
2023-06-21 23:38   ` Paul E. McKenney via lttng-dev
2023-06-07 18:53 ` [lttng-dev] [PATCH v2 09/12] tests/unit/test_build: Quiet unused return value Olivier Dion via lttng-dev
2023-06-07 18:53 ` [lttng-dev] [PATCH v2 10/12] urcu/annotate: Add CMM annotation Olivier Dion via lttng-dev
2023-06-07 18:53 ` [lttng-dev] [PATCH v2 11/12] Add cmm_emit_legacy_smp_mb() Olivier Dion via lttng-dev
2023-06-07 18:53 ` [lttng-dev] [PATCH v2 12/12] tests: Add tests for checking race conditions Olivier Dion via lttng-dev

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