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From: Will Deacon <will@kernel.org>
To: Peter Zijlstra <peterz@infradead.org>
Cc: "Jens Axboe" <axboe@kernel.dk>,
	"Carter Li 李通洲" <carter.li@eoitek.com>,
	"Pavel Begunkov" <asml.silence@gmail.com>,
	io-uring <io-uring@vger.kernel.org>,
	"Oleg Nesterov" <oleg@redhat.com>,
	"Mark Rutland" <mark.rutland@arm.com>,
	linux-kernel@vger.kernel.org
Subject: Re: [PATCH] asm-generic/atomic: Add try_cmpxchg() fallbacks
Date: Thu, 20 Feb 2020 10:39:35 +0000
Message-ID: <20200220103934.GA14459@willie-the-truck> (raw)
In-Reply-To: <20200220103727.GW18400@hirez.programming.kicks-ass.net>

On Thu, Feb 20, 2020 at 11:37:27AM +0100, Peter Zijlstra wrote:
> On Thu, Feb 20, 2020 at 10:30:45AM +0000, Will Deacon wrote:
> > On Tue, Feb 18, 2020 at 03:27:00PM +0100, Peter Zijlstra wrote:
> > > diff --git a/scripts/atomic/gen-atomic-fallback.sh b/scripts/atomic/gen-atomic-fallback.sh
> > > index b6c6f5d306a7..3c9be8d550e0 100755
> > > --- a/scripts/atomic/gen-atomic-fallback.sh
> > > +++ b/scripts/atomic/gen-atomic-fallback.sh
> > > @@ -140,6 +140,32 @@ cat <<EOF
> > >  EOF
> > >  }
> > >  
> > > +gen_try_cmpxchg_fallback()
> > > +{
> > > +	local order="$1"; shift;
> > > +
> > > +cat <<EOF
> > > +#ifndef try_cmpxchg${order}
> > > +#define try_cmpxchg${order}(_ptr, _oldp, _new) \\
> > > +({ \\
> > > +	typeof(*ptr) ___r, ___o = *(_oldp); \\
> > > +	___r = cmpxchg${order}((_ptr), ___o, (_new)); \\
> > > +	if (unlikely(___r != ___o)) \\
> > > +		*(_old) = ___r; \\
> > 
> > This doesn't compile because _old isn't declared. Probably best to avoid
> > evaluating _oldp twice though.
> 
> Compiler had already spotted that, I'll make it something like:
> 
> 	typeof(*ptr) *___op = (_oldp), ___o = *___op;
> 
> 	...
> 
> 		*___op = ___r;
> 
> Which avoids the double eval.

Cool, you can stick my Ack on the patch with that change.

Will

  reply index

Thread overview: 59+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-02-12 16:31 [ISSUE] The time cost of IOSQE_IO_LINK Carter Li 李通洲
2020-02-12 17:11 ` Jens Axboe
2020-02-12 17:22   ` Jens Axboe
2020-02-12 17:29     ` Jens Axboe
2020-02-13  0:33   ` Carter Li 李通洲
2020-02-13 15:08     ` Pavel Begunkov
2020-02-13 15:14       ` Jens Axboe
2020-02-13 15:51         ` Carter Li 李通洲
2020-02-14  1:25           ` Carter Li 李通洲
2020-02-14  2:45             ` Jens Axboe
2020-02-14  5:03               ` Jens Axboe
2020-02-14 15:32                 ` Peter Zijlstra
2020-02-14 15:47                   ` Jens Axboe
2020-02-14 16:18                     ` Jens Axboe
2020-02-14 17:52                       ` Jens Axboe
2020-02-14 20:44                         ` Jens Axboe
2020-02-15  0:16                           ` Carter Li 李通洲
2020-02-15  1:10                             ` Jens Axboe
2020-02-15  1:25                               ` Carter Li 李通洲
2020-02-15  1:27                                 ` Jens Axboe
2020-02-15  6:01                                   ` Jens Axboe
2020-02-15  6:32                                     ` Carter Li 李通洲
2020-02-15 15:11                                       ` Jens Axboe
2020-02-16 19:06                                     ` Pavel Begunkov
2020-02-16 22:23                                       ` Jens Axboe
2020-02-17 10:30                                         ` Pavel Begunkov
2020-02-17 19:30                                           ` Jens Axboe
2020-02-16 23:06                                       ` Jens Axboe
2020-02-16 23:07                                         ` Jens Axboe
2020-02-17 12:09                           ` Peter Zijlstra
2020-02-17 16:12                             ` Jens Axboe
2020-02-17 17:16                               ` Jens Axboe
2020-02-17 17:46                                 ` Peter Zijlstra
2020-02-17 18:16                                   ` Jens Axboe
2020-02-18 13:13                                     ` Peter Zijlstra
2020-02-18 14:27                                       ` [PATCH] asm-generic/atomic: Add try_cmpxchg() fallbacks Peter Zijlstra
2020-02-18 14:40                                         ` Peter Zijlstra
2020-02-20 10:30                                         ` Will Deacon
2020-02-20 10:37                                           ` Peter Zijlstra
2020-02-20 10:39                                             ` Will Deacon [this message]
2020-02-18 14:56                                       ` [ISSUE] The time cost of IOSQE_IO_LINK Oleg Nesterov
2020-02-18 15:07                                         ` Oleg Nesterov
2020-02-18 15:38                                           ` Peter Zijlstra
2020-02-18 16:33                                             ` Jens Axboe
2020-02-18 15:07                                         ` Peter Zijlstra
2020-02-18 15:50                                           ` [PATCH] task_work_run: don't take ->pi_lock unconditionally Oleg Nesterov
2020-02-20 16:39                                             ` Peter Zijlstra
2020-02-20 17:22                                               ` Oleg Nesterov
2020-02-20 17:49                                                 ` Peter Zijlstra
2020-02-21 14:52                                                   ` Oleg Nesterov
2020-02-24 18:47                                                     ` Jens Axboe
2020-02-28 19:17                                                       ` Jens Axboe
2020-02-28 19:25                                                         ` Peter Zijlstra
2020-02-28 19:28                                                           ` Jens Axboe
2020-02-28 20:06                                                             ` Peter Zijlstra
2020-02-28 20:15                                                               ` Jens Axboe
2020-02-18 16:46                                       ` [ISSUE] The time cost of IOSQE_IO_LINK Jens Axboe
2020-02-18 16:52                                         ` Jens Axboe
2020-02-18 13:13                               ` Peter Zijlstra

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