From: Andreas Schwab <schwab@linux-m68k.org>
To: "H.J. Lu via Libc-alpha" <libc-alpha@sourceware.org>
Subject: Re: [PATCH] x86: Optimize atomic_compare_and_exchange_[val|bool]_acq [BZ #28537]
Date: Wed, 03 Nov 2021 16:14:35 +0100 [thread overview]
Message-ID: <87zgql1db8.fsf@igel.home> (raw)
In-Reply-To: <20211103150415.1211388-1-hjl.tools@gmail.com> (H. J. Lu via Libc-alpha's message of "Wed, 3 Nov 2021 08:04:15 -0700")
On Nov 03 2021, H.J. Lu via Libc-alpha wrote:
> diff --git a/sysdeps/x86/atomic-machine.h b/sysdeps/x86/atomic-machine.h
> index 2692d94a92..92c7cf58b7 100644
> --- a/sysdeps/x86/atomic-machine.h
> +++ b/sysdeps/x86/atomic-machine.h
> @@ -73,9 +73,19 @@ typedef uintmax_t uatomic_max_t;
> #define ATOMIC_EXCHANGE_USES_CAS 0
>
> #define atomic_compare_and_exchange_val_acq(mem, newval, oldval) \
> - __sync_val_compare_and_swap (mem, oldval, newval)
> + ({ __typeof (*(mem)) oldmem = *(mem), ret; \
> + ret = (oldmem == (oldval) \
> + ? __sync_val_compare_and_swap (mem, oldval, newval) \
> + : oldmem); \
> + ret; })
Can't this cause the CAS to fail spuriously if the compiler used
some stale cached value for *mem?
Andreas.
--
Andreas Schwab, schwab@linux-m68k.org
GPG Key fingerprint = 7578 EB47 D4E5 4D69 2510 2552 DF73 E780 A9DA AEC1
"And now for something completely different."
next prev parent reply other threads:[~2021-11-03 18:00 UTC|newest]
Thread overview: 23+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-11-03 15:04 H.J. Lu
2021-11-03 15:14 ` Andreas Schwab [this message]
2021-11-03 15:50 ` Oleh Derevenko
2021-11-03 16:59 ` Arjan van de Ven
2021-11-03 17:17 ` Andreas Schwab
2021-11-03 19:21 ` Arjan van de Ven
2021-11-03 19:48 ` H.J. Lu
2021-11-03 20:38 ` Oleh Derevenko
2021-11-03 22:12 ` H.J. Lu
2021-11-04 8:58 ` Oleh Derevenko
2021-11-04 9:44 ` Oleh Derevenko
2021-11-03 17:26 ` Oleh Derevenko
2021-11-03 17:30 ` Arjan van de Ven
2021-11-03 17:55 ` Oleh Derevenko
2021-11-03 19:22 ` Arjan van de Ven
2021-11-04 11:42 ` Oleh Derevenko
2021-11-04 14:15 ` Arjan van de Ven
2021-11-03 16:35 ` Florian Weimer
2021-11-03 19:13 ` H.J. Lu
2021-11-04 10:15 ` Florian Weimer
2021-11-04 14:31 ` H.J. Lu
2021-11-04 14:59 ` H.J. Lu
2021-11-03 17:25 ` Noah Goldstein
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