Messages in this thread | | | From | Geert Uytterhoeven <> | Date | Thu, 22 Dec 2022 15:12:19 +0100 | Subject | Re: [PATCH 00/19] Introduce __xchg, non-atomic xchg |
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Hi Andrzej,
Thanks for your series!
On Thu, Dec 22, 2022 at 12:49 PM Andrzej Hajda <andrzej.hajda@intel.com> 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);
?
> 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
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