From: David Laight <David.Laight@ACULAB.COM>
To: 'Segher Boessenkool' <segher@kernel.crashing.org>,
Christophe Leroy <christophe.leroy@csgroup.eu>
Cc: Paul Mackerras <paulus@samba.org>,
"linuxppc-dev@lists.ozlabs.org" <linuxppc-dev@lists.ozlabs.org>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
Nicholas Piggin <npiggin@gmail.com>
Subject: RE: [PATCH v1 1/2] powerpc/bitops: Use immediate operand when possible
Date: Wed, 14 Apr 2021 15:32:04 +0000 [thread overview]
Message-ID: <efcabc9410cf4d03b203749a02e5a935@AcuMS.aculab.com> (raw)
In-Reply-To: <20210414151921.GW26583@gate.crashing.org>
From: Segher Boessenkool
> Sent: 14 April 2021 16:19
...
> > Could the kernel use GCC builtin atomic functions instead ?
> >
> > https://gcc.gnu.org/onlinedocs/gcc/_005f_005fatomic-Builtins.html
>
> Certainly that should work fine for the simpler cases that the atomic
> operations are meant to provide. But esp. for not-so-simple cases the
> kernel may require some behaviour provided by the existing assembler
> implementation, and not by the atomic builtins.
>
> I'm not saying this cannot work, just that some serious testing will be
> needed. If it works it should be the best of all worlds, so then it is
> a really good idea yes :-)
I suspect they just add an extra layer of abstraction that makes it
even more difficult to verify and could easily get broken by a compiler
update (etc).
The other issue is that the code needs to be correct with compiled
with (for example) -O0.
That could very easily break anything except the asm implementation
if additional memory accesses and/or increased code size cause grief.
David
-
Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK
Registration No: 1397386 (Wales)
next prev parent reply other threads:[~2021-04-14 15:32 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-04-08 15:33 [PATCH v1 1/2] powerpc/bitops: Use immediate operand when possible Christophe Leroy
2021-04-08 15:33 ` [PATCH v1 2/2] powerpc/atomics: " Christophe Leroy
2021-04-12 22:08 ` Segher Boessenkool
2021-04-13 16:36 ` Christophe Leroy
2021-04-12 21:54 ` [PATCH v1 1/2] powerpc/bitops: " Segher Boessenkool
2021-04-13 16:33 ` Christophe Leroy
2021-04-13 21:58 ` Segher Boessenkool
2021-04-14 2:01 ` Nicholas Piggin
2021-04-14 12:24 ` Segher Boessenkool
2021-04-14 12:42 ` Christophe Leroy
2021-04-14 15:19 ` Segher Boessenkool
2021-04-14 15:32 ` David Laight [this message]
2021-04-14 17:20 ` Segher Boessenkool
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=efcabc9410cf4d03b203749a02e5a935@AcuMS.aculab.com \
--to=david.laight@aculab.com \
--cc=christophe.leroy@csgroup.eu \
--cc=linux-kernel@vger.kernel.org \
--cc=linuxppc-dev@lists.ozlabs.org \
--cc=npiggin@gmail.com \
--cc=paulus@samba.org \
--cc=segher@kernel.crashing.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).