On Thu, 22 Dec 2022 12:46:16 +0100 Andrzej Hajda <andrzej.hajda@xxxxxxxxx> wrote:
Hi all,So to clarify, the intent here is a simple readability cleanup for
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.
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.I like replace(), or, shockingly, exchange().
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.
But... Can we simply make swap() return the previous value?
previous_min_rate = swap(&evport->qos.min_rate, min_rate);