From: "H.J. Lu" <hjl.tools@gmail.com>
To: Wilco Dijkstra <Wilco.Dijkstra@arm.com>
Cc: Adhemerval Zanella Netto <adhemerval.zanella@linaro.org>,
Noah Goldstein <goldstein.w.n@gmail.com>,
GNU C Library <libc-alpha@sourceware.org>
Subject: Re: [PATCH 3/7] Remove atomic_bit_set/bit_test_set
Date: Tue, 12 Jul 2022 12:11:07 -0700 [thread overview]
Message-ID: <CAMe9rOrkO0MyGt4MzePsQ52+=UYo9WhO9W25WBMgpxUYVLtoNw@mail.gmail.com> (raw)
In-Reply-To: <AM5PR0801MB1668554E558E9C60A283A19C83869@AM5PR0801MB1668.eurprd08.prod.outlook.com>
On Tue, Jul 12, 2022 at 11:44 AM Wilco Dijkstra <Wilco.Dijkstra@arm.com> wrote:
>
> Hi,
>
> I don't believe it could make a difference since it isn't performance critical code.
> Note that several similar fetch_or/fetch_and are used which do not optimize into a
Only the operations with test have this issue. Simple fetch_or and
fetch_and are
OK.
> bitset operation, so even if we fix this particular case to use unsigned, there are many
> others. IIRC there is even a fetch_or with zero which is kind of useless!
>
> More importantly, it raises a question for locking: we currently use a compare-exchange
> for each lock and unlock. If compare-exchange has higher overheads than other atomics
> then we should investigate more efficient locking sequences.
compare-exchange can be very expensive under contention.
> Cheers,
> Wilco
--
H.J.
next prev parent reply other threads:[~2022-07-12 19:11 UTC|newest]
Thread overview: 18+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-07-06 15:14 Wilco Dijkstra
2022-07-06 16:14 ` Noah Goldstein
2022-07-06 18:25 ` Noah Goldstein
2022-07-06 18:59 ` Wilco Dijkstra
2022-07-06 19:14 ` Noah Goldstein
2022-07-06 19:30 ` H.J. Lu
2022-07-06 19:36 ` Wilco Dijkstra
2022-07-06 19:51 ` Noah Goldstein
2022-07-06 19:56 ` Noah Goldstein
2022-07-06 20:14 ` Wilco Dijkstra
2022-07-06 20:30 ` Noah Goldstein
2022-07-06 20:56 ` H.J. Lu
2022-07-12 17:47 ` Adhemerval Zanella Netto
2022-07-12 18:09 ` H.J. Lu
2022-07-12 18:44 ` Wilco Dijkstra
2022-07-12 19:11 ` H.J. Lu [this message]
2022-07-12 19:18 ` Noah Goldstein
2022-07-12 20:39 ` Wilco Dijkstra
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