From: Duncan Sands via lttng-dev <lttng-dev@lists.lttng.org>
To: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>,
lttng-dev@lists.lttng.org
Subject: Re: [lttng-dev] [PATCH 2/7] Use gcc __atomic builtis for <urcu/uatomic.h> implementation
Date: Wed, 22 Mar 2023 09:24:35 +0100 [thread overview]
Message-ID: <2baf2296-2be2-a4ed-60a5-b87335acd0f8@free.fr> (raw)
In-Reply-To: <86858b96-5b88-7e1c-2be2-6157e864c8db@efficios.com>
Hi Mathieu,
> Tested on godbolt.org with:
>
> int a;
>
> void fct(void)
> {
> (void) __atomic_add_fetch(&a, 1, __ATOMIC_RELAXED);
> __atomic_thread_fence(__ATOMIC_SEQ_CST);
> }
>
> x86-64 gcc 12.2 -O2 -std=c11:
>
> fct:
> lock add DWORD PTR a[rip], 1
> lock or QWORD PTR [rsp], 0
> ret
> a:
> .zero 4
that's disappointing. It's the same if both use __ATOMIC_SEQ_CST:
int a;
void fct(void)
{
(void) __atomic_add_fetch(&a, 1, __ATOMIC_SEQ_CST);
__atomic_thread_fence(__ATOMIC_SEQ_CST);
}
->
fct():
lock add DWORD PTR a[rip], 1
lock or QWORD PTR [rsp], 0
ret
a:
.zero 4
on x86-64 gcc 12.2 -O2 -std=c11. Clang also doesn't optimize the fence away.
Best wishes, Duncan.
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next prev parent reply other threads:[~2023-03-22 8:25 UTC|newest]
Thread overview: 32+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-03-17 21:37 [lttng-dev] [PATCH 0/7] Replace the custom code with gcc/clang __atomic builtins Ondřej Surý via lttng-dev
2023-03-17 21:37 ` [lttng-dev] [PATCH 1/7] Require __atomic builtins to build Ondřej Surý via lttng-dev
2023-03-17 21:37 ` [lttng-dev] [PATCH 2/7] Use gcc __atomic builtis for <urcu/uatomic.h> implementation Ondřej Surý via lttng-dev
2023-03-20 18:03 ` Mathieu Desnoyers via lttng-dev
2023-03-20 18:13 ` Mathieu Desnoyers via lttng-dev
2023-03-20 18:28 ` Ondřej Surý via lttng-dev
2023-03-20 18:38 ` Mathieu Desnoyers via lttng-dev
2023-03-20 18:41 ` Mathieu Desnoyers via lttng-dev
2023-03-20 19:38 ` Duncan Sands via lttng-dev
2023-03-21 20:26 ` Mathieu Desnoyers via lttng-dev
2023-03-22 8:24 ` Duncan Sands via lttng-dev [this message]
2023-03-17 21:37 ` [lttng-dev] [PATCH 3/7] Use __atomic_thread_fence() for cmm_barrier() Ondřej Surý via lttng-dev
2023-03-20 18:06 ` Mathieu Desnoyers via lttng-dev
2023-03-20 18:14 ` Mathieu Desnoyers via lttng-dev
2023-03-17 21:37 ` [lttng-dev] [PATCH 4/7] Replace the internal pointer manipulation with __atomic builtins Ondřej Surý via lttng-dev
2023-03-20 18:25 ` Mathieu Desnoyers via lttng-dev
2023-03-17 21:37 ` [lttng-dev] [PATCH 5/7] Use __atomic builtins to implement CMM_{LOAD, STORE}_SHARED Ondřej Surý via lttng-dev
2023-03-20 18:28 ` Mathieu Desnoyers via lttng-dev
2023-03-17 21:37 ` [lttng-dev] [PATCH 6/7] Fix: uatomic_or() need retyping to uintptr_t in rculfhash.c Ondřej Surý via lttng-dev
2023-03-20 18:31 ` Mathieu Desnoyers via lttng-dev
2023-03-21 10:15 ` Ondřej Surý via lttng-dev
2023-03-21 14:44 ` Mathieu Desnoyers via lttng-dev
2023-03-21 14:45 ` Mathieu Desnoyers via lttng-dev
2023-03-17 21:37 ` [lttng-dev] [PATCH 7/7] Experiment: Add explicit memory barrier in free_completion() Ondřej Surý via lttng-dev
2023-03-20 18:37 ` Mathieu Desnoyers via lttng-dev
2023-03-21 10:21 ` Ondřej Surý via lttng-dev
2023-03-21 14:46 ` Mathieu Desnoyers via lttng-dev
2023-03-21 14:48 ` Ondřej Surý via lttng-dev
2023-03-21 14:49 ` Mathieu Desnoyers via lttng-dev
2023-03-21 14:59 ` [lttng-dev] TSAN and the tests Ondřej Surý via lttng-dev
-- strict thread matches above, loose matches on Subject: below --
2023-03-21 13:30 [lttng-dev] (no subject) Ondřej Surý via lttng-dev
2023-03-21 13:30 ` [lttng-dev] [PATCH 2/7] Use gcc __atomic builtis for <urcu/uatomic.h> implementation Ondřej Surý via lttng-dev
2023-03-21 20:03 ` Mathieu Desnoyers via lttng-dev
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