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From: Peter Zijlstra <peterz@infradead.org>
To: Ingo Molnar <mingo@kernel.org>
Cc: Mark Rutland <mark.rutland@arm.com>,
	linux-arm-kernel@lists.infradead.org,
	linux-kernel@vger.kernel.org, aryabinin@virtuozzo.com,
	boqun.feng@gmail.com, catalin.marinas@arm.com,
	dvyukov@google.com, will.deacon@arm.com
Subject: Re: [PATCH] locking/atomics: Clean up the atomic.h maze of #defines
Date: Sat, 5 May 2018 11:24:38 +0200	[thread overview]
Message-ID: <20180505092438.GB12217@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <20180505090403.p2ywuen42rnlwizq@gmail.com>

On Sat, May 05, 2018 at 11:04:03AM +0200, Ingo Molnar wrote:
> 
> * Peter Zijlstra <peterz@infradead.org> wrote:
> 
> > > So we could do the following simplification on top of that:
> > > 
> > >  #ifndef atomic_fetch_dec_relaxed
> > >  # ifndef atomic_fetch_dec
> > >  #  define atomic_fetch_dec(v)		atomic_fetch_sub(1, (v))
> > >  #  define atomic_fetch_dec_relaxed(v)	atomic_fetch_sub_relaxed(1, (v))
> > >  #  define atomic_fetch_dec_acquire(v)	atomic_fetch_sub_acquire(1, (v))
> > >  #  define atomic_fetch_dec_release(v)	atomic_fetch_sub_release(1, (v))
> > >  # else
> > >  #  define atomic_fetch_dec_relaxed		atomic_fetch_dec
> > >  #  define atomic_fetch_dec_acquire		atomic_fetch_dec
> > >  #  define atomic_fetch_dec_release		atomic_fetch_dec
> > >  # endif
> > >  #else
> > >  # ifndef atomic_fetch_dec
> > >  #  define atomic_fetch_dec(...)		__atomic_op_fence(atomic_fetch_dec, __VA_ARGS__)
> > >  #  define atomic_fetch_dec_acquire(...)	__atomic_op_acquire(atomic_fetch_dec, __VA_ARGS__)
> > >  #  define atomic_fetch_dec_release(...)	__atomic_op_release(atomic_fetch_dec, __VA_ARGS__)
> > >  # endif
> > >  #endif
> > 
> > This would disallow an architecture to override just fetch_dec_release for
> > instance.
> 
> Couldn't such a crazy arch just define _all_ the 3 APIs in this group?
> That's really a small price and makes the place pay the complexity
> price that does the weirdness...

I would expect the pattern where it can do all 'release' and/or all
'acquire' variants special but cannot use the __atomic_op_*() wrappery.

> > I don't think there currently is any architecture that does that, but the
> > intent was to allow it to override anything and only provide defaults where it
> > does not.
> 
> I'd argue that if a new arch only defines one of these APIs that's probably a bug. 
> If they absolutely want to do it, they still can - by defining all 3 APIs.
> 
> So there's no loss in arch flexibility.

Ideally we'd generate the whole mess.. and then allowing these extra few
overrides is not a problem at all.

> > None of this takes away the giant trainwreck that is the annotated atomic stuff
> > though.
> > 
> > And I seriously hate this one:
> > 
> >   ba1c9f83f633 ("locking/atomic/x86: Un-macro-ify atomic ops implementation")
> > 
> > and will likely undo that the moment I need to change anything there.
> 
> If it makes the code more readable then I don't object - the problem was that the 
> instrumentation indirection made all that code much harder to follow.

Thing is, it is all the exact same loop, and bitrot mandates they drift
over time. When I cleaned up all the architectures I found plenty cases
where there were spurious differences between things.

  reply	other threads:[~2018-05-05  9:24 UTC|newest]

Thread overview: 61+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-05-04 17:39 [PATCH 0/6] arm64: add instrumented atomics Mark Rutland
2018-05-04 17:39 ` [PATCH 1/6] locking/atomic, asm-generic: instrument ordering variants Mark Rutland
2018-05-04 18:01   ` Peter Zijlstra
2018-05-04 18:09     ` Mark Rutland
2018-05-04 18:24       ` Peter Zijlstra
2018-05-05  9:12         ` Mark Rutland
2018-05-05  8:11       ` [PATCH] locking/atomics: Clean up the atomic.h maze of #defines Ingo Molnar
2018-05-05  8:36         ` [PATCH] locking/atomics: Simplify the op definitions in atomic.h some more Ingo Molnar
2018-05-05  8:54           ` [PATCH] locking/atomics: Combine the atomic_andnot() and atomic64_andnot() API definitions Ingo Molnar
2018-05-06 12:15             ` [tip:locking/core] " tip-bot for Ingo Molnar
2018-05-06 14:15             ` [PATCH] " Andrea Parri
2018-05-06 12:14           ` [tip:locking/core] locking/atomics: Simplify the op definitions in atomic.h some more tip-bot for Ingo Molnar
2018-05-09  7:33             ` Peter Zijlstra
2018-05-09 13:03               ` Will Deacon
2018-05-15  8:54                 ` Ingo Molnar
2018-05-15  8:35               ` Ingo Molnar
2018-05-15 11:41                 ` Peter Zijlstra
2018-05-15 12:13                   ` Peter Zijlstra
2018-05-15 15:43                   ` Mark Rutland
2018-05-15 17:10                     ` Peter Zijlstra
2018-05-15 17:53                       ` Mark Rutland
2018-05-15 18:11                         ` Peter Zijlstra
2018-05-15 18:15                           ` Peter Zijlstra
2018-05-15 18:52                             ` Linus Torvalds
2018-05-15 19:39                               ` Peter Zijlstra
2018-05-21 17:12                           ` Mark Rutland
2018-05-06 14:12           ` [PATCH] " Andrea Parri
2018-05-06 14:57             ` Ingo Molnar
2018-05-07  9:54               ` Andrea Parri
2018-05-18 18:43               ` Palmer Dabbelt
2018-05-05  8:47         ` [PATCH] locking/atomics: Clean up the atomic.h maze of #defines Peter Zijlstra
2018-05-05  9:04           ` Ingo Molnar
2018-05-05  9:24             ` Peter Zijlstra [this message]
2018-05-05  9:38             ` Ingo Molnar
2018-05-05 10:00               ` [RFC PATCH] locking/atomics/powerpc: Introduce optimized cmpxchg_release() family of APIs for PowerPC Ingo Molnar
2018-05-05 10:26                 ` Boqun Feng
2018-05-06  1:56                 ` Benjamin Herrenschmidt
2018-05-05 10:16               ` [PATCH] locking/atomics: Clean up the atomic.h maze of #defines Boqun Feng
2018-05-05 10:35                 ` [RFC PATCH] locking/atomics/powerpc: Clarify why the cmpxchg_relaxed() family of APIs falls back to full cmpxchg() Ingo Molnar
2018-05-05 11:28                   ` Boqun Feng
2018-05-05 13:27                     ` [PATCH] locking/atomics/powerpc: Move cmpxchg helpers to asm/cmpxchg.h and define the full set of cmpxchg APIs Ingo Molnar
2018-05-05 14:03                       ` Boqun Feng
2018-05-06 12:11                         ` Ingo Molnar
2018-05-07  1:04                           ` Boqun Feng
2018-05-07  6:50                             ` Ingo Molnar
2018-05-06 12:13                     ` [tip:locking/core] " tip-bot for Boqun Feng
2018-05-07 13:31                       ` [PATCH v2] " Boqun Feng
2018-05-05  9:05           ` [PATCH] locking/atomics: Clean up the atomic.h maze of #defines Dmitry Vyukov
2018-05-05  9:32             ` Peter Zijlstra
2018-05-07  6:43               ` [RFC PATCH] locking/atomics/x86/64: Clean up and fix details of <asm/atomic64_64.h> Ingo Molnar
2018-05-05  9:09           ` [PATCH] locking/atomics: Clean up the atomic.h maze of #defines Ingo Molnar
2018-05-05  9:29             ` Peter Zijlstra
2018-05-05 10:48               ` [PATCH] locking/atomics: Shorten the __atomic_op() defines to __op() Ingo Molnar
2018-05-05 10:59                 ` Ingo Molnar
2018-05-06 12:15                 ` [tip:locking/core] " tip-bot for Ingo Molnar
2018-05-06 12:14         ` [tip:locking/core] locking/atomics: Clean up the atomic.h maze of #defines tip-bot for Ingo Molnar
2018-05-04 17:39 ` [PATCH 2/6] locking/atomic, asm-generic: instrument atomic*andnot*() Mark Rutland
2018-05-04 17:39 ` [PATCH 3/6] arm64: use <linux/atomic.h> for cmpxchg Mark Rutland
2018-05-04 17:39 ` [PATCH 4/6] arm64: fix assembly constraints " Mark Rutland
2018-05-04 17:39 ` [PATCH 5/6] arm64: use instrumented atomics Mark Rutland
2018-05-04 17:39 ` [PATCH 6/6] arm64: instrument smp_{load_acquire,store_release} Mark Rutland

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