From mboxrd@z Thu Jan 1 00:00:00 1970 From: Andrzej Hajda Date: Thu, 22 Dec 2022 14:17:18 +0000 Subject: Re: [PATCH 00/19] Introduce __xchg, non-atomic xchg Message-Id: <286f817c-2e3a-aba9-1083-73f25bafd84c@intel.com> List-Id: References: <20221222114635.1251934-1-andrzej.hajda@intel.com> In-Reply-To: MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: Geert Uytterhoeven Cc: 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@lists.linux-m68k.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 , Rodrigo Vivi , Andrew Morton , Andy Shevchenko , Peter Zijlstra , Boqun Feng , Mark Rutland On 22.12.2022 15:12, Geert Uytterhoeven wrote: > Hi Andrzej, > > Thanks for your series! > > On Thu, Dec 22, 2022 at 12:49 PM Andrzej Hajda wrote: >> 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. >> I am not sure who is good person to review/ack such patches, >> 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); > Upon closer look, shouldn't that be > > previous_min_rate = __xchg(&evport->qos.min_rate, min_rate); > > ? Yes, you are right, the first argument is a pointer. Regards Andrzej > >> 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. > Before I realized the missing "&", I wondered how this is different > from swap(), so naming is important. > https://elixir.bootlin.com/linux/latest/source/include/linux/minmax.h#L139 > > Gr{oetje,eeting}s, > > Geert > > -- > Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org > > In personal conversations with technical people, I call myself a hacker. But > when I'm talking to journalists I just say "programmer" or something like that. > -- Linus Torvalds