Re: [Intel-gfx] [PATCH 1/5] linux/minmax.h: add non-atomic version of xchg

[Andrzej Hajda]

On 09.12.2022 19:56, Andy Shevchenko wrote:
> On Fri, Dec 09, 2022 at 04:48:39PM +0100, Andrzej Hajda wrote:
> > The pattern of setting variable with new value and returning old
> > one is very common in kernel. Usually atomicity of the operation
> > is not required, so xchg seems to be suboptimal and confusing in
> > such cases. Since name xchg is already in use and __xchg is used
> > in architecture code, proposition is to name the macro exchange.
> >
> > Signed-off-by: Andrzej Hajda <andrzej.hajda@xxxxxxxxx>
> > ---
> > Hi,
> >
> > 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 used, of course I do not intend to do it :).
> >
> > I was not sure where to put this macro, I hope near swap definition
> > is the most suitable place.
>
> Ah, swap() in this context is not the same. minmax.h hosts it because
> it's often related to the swap function in the sort-type algorithms. > >> Moreover sorry if to/cc is not correct - get_maintainers.pl was
> > more confused than me, to who address this patch.
>
> ...
>
> >   include/linux/minmax.h | 14 ++++++++++++++
>
> Does it really suit this header? I would expect something else.
> Maybe include/linux/non-atomic/xchg.h, dunno.

non-atomic seems quite strange for me, I would assume everything not in 
atomic is non-atomic, unless explicitly specified.

> Btw, have you looked if Ingo's gigantic series have done anything to cmpxchg.h
> and related headers? Maybe some ideas can be taken from there?

Grepping it didn't give any clue.

Looking at 'near' languages just to get an idea (they name the function 
differently):

C++ [1]: exchange and swap are in utility header
Rust[2]: replace and swap are in std::mem module

This is some argument to put them together.

[1]: https://en.cppreference.com/w/cpp/header/utility
[2]: https://doc.rust-lang.org/std/mem/index.html

Regards
Andrzej