From: Mark Rutland <mark.rutland@arm.com>
To: Peter Zijlstra <peterz@infradead.org>
Cc: will@kernel.org, boqun.feng@gmail.com,
linux-kernel@vger.kernel.org, x86@kernel.org, elver@google.com,
keescook@chromium.org, hch@infradead.org,
torvalds@linux-foundation.org, axboe@kernel.dk
Subject: Re: [PATCH v2 3/9] atomic: Introduce atomic_{inc,dec,dec_and_test}_overflow()
Date: Mon, 13 Dec 2021 11:09:03 +0000 [thread overview]
Message-ID: <Ybcpz1XIU8+EtSV3@FVFF77S0Q05N> (raw)
In-Reply-To: <YbcnpAjgJSRIAduN@hirez.programming.kicks-ass.net>
On Mon, Dec 13, 2021 at 11:59:48AM +0100, Peter Zijlstra wrote:
> On Mon, Dec 13, 2021 at 10:06:01AM +0000, Mark Rutland wrote:
> > On Fri, Dec 10, 2021 at 05:16:21PM +0100, Peter Zijlstra wrote:
>
> > > +#ifndef arch_atomic_inc_overflow
> > > +#define arch_atomic_inc_overflow(_v, _label) \
> > > +do { \
> > > + int __old = arch_atomic_fetch_inc(_v); \
> > > + if (unlikely(__old <= 0)) \
> > > + goto _label; \
> > > +} while (0)
> > > +#endif
> > > +
> > > +#ifndef arch_atomic_dec_overflow
> > > +#define arch_atomic_dec_overflow(_v, _label) \
> > > +do { \
> > > + int __new = arch_atomic_dec_return(_v); \
> > > + if (unlikely(__new <= 0)) \
> > > + goto _label; \
> > > +} while (0)
> > > +#endif
> > > +
> > > +#ifndef arch_atomic_dec_and_test_overflow
> > > +#define arch_atomic_dec_and_test_overflow(_v, _label) \
> > > +({ \
> > > + bool __ret = false; \
> > > + int __new = arch_atomic_dec_return(_v); \
> > > + if (unlikely(__new < 0)) \
> > > + goto _label; \
> > > + if (unlikely(__new == 0)) \
> > > + __ret = true; \
> > > + __ret; \
> > > +})
> > > +#endif
> >
> > I had wanted to move at least part of this to a function to ensure
> > single-evaluation and avoid accidental symbol aliasing, but (as we discussed
> > over IRC) I couldn't find any good way to do so, and given this is sufficiently
> > specialise I think we should be ok with this as-is. It's certainly no worse
> > than the existing stuff for xchg/cmpxchg.
>
> Right, as you know I tried the same :-) Anyway, the above macros should
> be free of multi-evaluation issues, both _v and _label are only used the
> once. Aliassing is always a possibility but minimized by __ prefixing
> the local variables.
Agreed! I just wanted something archived in the thread mentioning that this was
the only practical option.
I agree that as this stands we're not doing anything sufficiently complicated
enough to worry about multi-evaluation, and that the underscores should be
sufficient to avoid aliasing in practice.
Mark.
next prev parent reply other threads:[~2021-12-13 11:09 UTC|newest]
Thread overview: 34+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-12-10 16:16 [PATCH v2 0/9] refcount: Improve code-gen Peter Zijlstra
2021-12-10 16:16 ` [PATCH v2 1/9] atomic: Prepare scripts for macro ops Peter Zijlstra
2021-12-10 17:27 ` Mark Rutland
2021-12-10 17:43 ` Marco Elver
2021-12-10 16:16 ` [PATCH v2 2/9] atomic: Add xchg.tbl Peter Zijlstra
2021-12-13 9:50 ` Mark Rutland
2021-12-10 16:16 ` [PATCH v2 3/9] atomic: Introduce atomic_{inc,dec,dec_and_test}_overflow() Peter Zijlstra
2021-12-13 10:06 ` Mark Rutland
2021-12-13 10:57 ` Peter Zijlstra
2021-12-13 10:59 ` Peter Zijlstra
2021-12-13 11:09 ` Mark Rutland [this message]
2021-12-10 16:16 ` [PATCH v2 4/9] refcount: Use atomic_*_overflow() Peter Zijlstra
2021-12-13 10:35 ` Mark Rutland
2021-12-10 16:16 ` [PATCH v2 5/9] atomic,x86: Implement atomic_dec_and_test_overflow() Peter Zijlstra
2021-12-13 11:04 ` Mark Rutland
2021-12-10 16:16 ` [PATCH v2 6/9] refcount: Fix refcount_dec_not_one() Peter Zijlstra
2021-12-10 16:16 ` [PATCH v2 7/9] refcount: Prepare for atomic_*_overflow() offsets Peter Zijlstra
2021-12-10 16:16 ` [PATCH v2 8/9] atomic,x86: Alternative atomic_*_overflow() scheme Peter Zijlstra
2021-12-10 16:53 ` Linus Torvalds
2021-12-10 17:27 ` Linus Torvalds
2021-12-17 3:38 ` Herbert Xu
2021-12-13 16:43 ` Peter Zijlstra
2021-12-13 17:29 ` Marco Elver
2021-12-13 18:11 ` Linus Torvalds
2021-12-13 18:18 ` Marco Elver
2021-12-13 18:24 ` Linus Torvalds
2021-12-13 19:35 ` Marco Elver
2021-12-13 18:21 ` Linus Torvalds
2021-12-10 16:16 ` [PATCH v2 9/9] refcount: Optimize __refcount_add_not_zero(.i=1) Peter Zijlstra
2021-12-10 19:37 ` [PATCH v2 0/9] refcount: Improve code-gen Peter Zijlstra
2021-12-13 12:15 ` [PATCH v2 10/9] atomic: Document the atomic_{}_overflow() functions Peter Zijlstra
2021-12-13 12:20 ` [PATCH v2 0/9] refcount: Improve code-gen Peter Zijlstra
2021-12-13 14:42 ` Marco Elver
2021-12-13 16:11 ` Peter Zijlstra
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=Ybcpz1XIU8+EtSV3@FVFF77S0Q05N \
--to=mark.rutland@arm.com \
--cc=axboe@kernel.dk \
--cc=boqun.feng@gmail.com \
--cc=elver@google.com \
--cc=hch@infradead.org \
--cc=keescook@chromium.org \
--cc=linux-kernel@vger.kernel.org \
--cc=peterz@infradead.org \
--cc=torvalds@linux-foundation.org \
--cc=will@kernel.org \
--cc=x86@kernel.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 an external index of several public inboxes,
see mirroring instructions on how to clone and mirror
all data and code used by this external index.