From: Alexander Lobakin <alexandr.lobakin@intel.com>
To: Andrew Morton <akpm@linux-foundation.org>
Cc: Alexander Lobakin <alexandr.lobakin@intel.com>,
Andrzej Hajda <andrzej.hajda@intel.com>,
linux-alpha@vger.kernel.org, linux-kernel@vger.kernel.org,
linux-snps-arc@lists.infradead.org,
linux-arm-kernel@lists.infradead.org,
linux-hexagon@vger.kernel.org, linux-ia64@vger.kernel.org,
loongarch@lists.linux.dev, linux-m68k@vger.kernel.org,
linux-mips@vger.kernel.org, openrisc@lists.librecores.org,
linux-parisc@vger.kernel.org, linuxppc-dev@lists.ozlabs.org,
linux-riscv@lists.infradead.org, linux-s390@vger.kernel.org,
linux-sh@vger.kernel.org, sparclinux@vger.kernel.org,
linux-xtensa@linux-xtensa.org, intel-gfx@lists.freedesktop.org,
dri-devel@lists.freedesktop.org, Arnd Bergmann <arnd@arndb.de>,
Rodrigo Vivi <rodrigo.vivi@intel.com>,
Andy Shevchenko <andriy.shevchenko@linux.intel.com>,
Peter Zijlstra <peterz@infradead.org>,
Boqun Feng <boqun.feng@gmail.com>,
Mark Rutland <mark.rutland@arm.com>
Subject: Re: [PATCH 00/19] Introduce __xchg, non-atomic xchg
Date: Fri, 23 Dec 2022 15:23:00 +0100 [thread overview]
Message-ID: <20221223142300.1820652-1-alexandr.lobakin@intel.com> (raw)
In-Reply-To: <20221222092147.d2bb177c67870884f2e59a9b@linux-foundation.org>
From: Andrew Morton <akpm@linux-foundation.org>
Date: Thu, 22 Dec 2022 09:21:47 -0800
> On Thu, 22 Dec 2022 12:46:16 +0100 Andrzej Hajda <andrzej.hajda@intel.com> wrote:
>
> > Hi all,
> >
> > I hope there will be place for such tiny helper in kernel.
> > Quick cocci analyze shows there is probably few thousands places
> > where it could be useful.
>
> So to clarify, the intent here is a simple readability cleanup for
> existing open-coded exchange operations. The intent is *not* to
> identify existing xchg() sites which are unnecessarily atomic and to
> optimize them by using the non-atomic version.
>
> Have you considered the latter?
>
> > I am not sure who is good person to review/ack such patches,
>
> I can take 'em.
>
> > so I've used my intuition to construct to/cc lists, sorry for mistakes.
> > This is the 2nd approach of the same idea, with comments addressed[0].
> >
> > The helper is tiny and there are advices we can leave without it, so
> > I want to present few arguments why it would be good to have it:
> >
> > 1. Code readability/simplification/number of lines:
> >
> > Real example from drivers/net/ethernet/mellanox/mlx5/core/esw/qos.c:
> > - previous_min_rate = evport->qos.min_rate;
> > - evport->qos.min_rate = min_rate;
> > + previous_min_rate = __xchg(evport->qos.min_rate, min_rate);
> >
> > For sure the code is more compact, and IMHO more readable.
> >
> > 2. Presence of similar helpers in other somehow related languages/libs:
> >
> > a) Rust[1]: 'replace' from std::mem module, there is also 'take'
> > helper (__xchg(&x, 0)), which is the same as private helper in
> > i915 - fetch_and_zero, see latest patch.
> > b) C++ [2]: 'exchange' from utility header.
> >
> > If the idea is OK there are still 2 qestions to answer:
> >
> > 1. Name of the helper, __xchg follows kernel conventions,
> > but for me Rust names are also OK.
>
> I like replace(), or, shockingly, exchange().
>
> But... Can we simply make swap() return the previous value?
>
> previous_min_rate = swap(&evport->qos.min_rate, min_rate);
Unforunately, swap()'s arguments get passed by names, not as
pointers, so you can't do
swap(some_ptr, NULL);
-- pretty common pattern for xchg.
Thanks,
Olek
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next prev parent reply other threads:[~2022-12-23 14:23 UTC|newest]
Thread overview: 41+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-12-22 11:46 [PATCH 00/19] Introduce __xchg, non-atomic xchg Andrzej Hajda
2022-12-22 11:46 ` [PATCH 01/19] arch/alpha: rename internal name __xchg to __arch_xchg Andrzej Hajda
2022-12-22 11:46 ` [PATCH 02/19] arch/arc: " Andrzej Hajda
2022-12-29 9:32 ` Arnd Bergmann
2022-12-29 11:33 ` [PATCH v2] arch: rename all internal names " Andrzej Hajda
2022-12-29 23:00 ` kernel test robot
2022-12-30 14:15 ` [PATCH v3] " Andrzej Hajda
2023-01-03 10:02 ` Heiko Carstens
2023-01-05 9:54 ` [PATCH v4] " Andrzej Hajda
2023-01-16 10:00 ` Geert Uytterhoeven
2023-01-02 8:30 ` [PATCH v2] " Geert Uytterhoeven
2022-12-22 11:46 ` [PATCH 03/19] arch/arm: rename internal name " Andrzej Hajda
2022-12-22 11:46 ` [PATCH 04/19] arch/arm64: " Andrzej Hajda
2022-12-22 11:46 ` [PATCH 05/19] arch/hexagon: " Andrzej Hajda
2022-12-22 11:46 ` [PATCH 06/19] arch/ia64: " Andrzej Hajda
2022-12-22 11:46 ` [PATCH 07/19] arch/loongarch: " Andrzej Hajda
2022-12-22 11:46 ` [PATCH 08/19] arch/m68k: " Andrzej Hajda
2022-12-22 11:46 ` [PATCH 09/19] arch/mips: " Andrzej Hajda
2022-12-22 11:46 ` [PATCH 10/19] arch/openrisc: " Andrzej Hajda
2022-12-22 11:46 ` [PATCH 11/19] arch/parisc: " Andrzej Hajda
2022-12-22 11:46 ` [PATCH 12/19] arch/powerpc: correct logged function names in xchg helpers Andrzej Hajda
2022-12-22 11:46 ` [PATCH 13/19] arch/riscv: rename internal name __xchg to __arch_xchg Andrzej Hajda
2022-12-29 16:22 ` Palmer Dabbelt
2023-02-15 5:22 ` Palmer Dabbelt
2022-12-22 11:46 ` [PATCH 14/19] arch/s390: " Andrzej Hajda
2022-12-22 11:46 ` [PATCH 15/19] arch/sh: " Andrzej Hajda
2022-12-22 11:46 ` [PATCH 16/19] arch/sparc: " Andrzej Hajda
2022-12-22 11:46 ` [PATCH 17/19] arch/xtensa: " Andrzej Hajda
2022-12-22 11:46 ` [PATCH 18/19] linux/include: add non-atomic version of xchg Andrzej Hajda
2022-12-22 12:47 ` Andy Shevchenko
2022-12-22 11:46 ` [PATCH 19/19] drm/i915/gt: use __xchg instead of internal helper Andrzej Hajda
2022-12-22 14:12 ` [PATCH 00/19] Introduce __xchg, non-atomic xchg Geert Uytterhoeven
2022-12-22 14:17 ` Andrzej Hajda
2022-12-22 17:21 ` Andrew Morton
2022-12-23 14:23 ` Alexander Lobakin [this message]
2022-12-29 9:54 ` Andrzej Hajda
2023-01-05 16:29 ` Daniel Vetter
2023-01-10 10:53 ` [RFC DO NOT MERGE] treewide: use __xchg in most obvious places Andrzej Hajda
2023-01-10 11:07 ` Andy Shevchenko
2023-01-10 12:46 ` [Intel-gfx] " Andrzej Hajda
2023-01-10 13:52 ` Andy Shevchenko
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