On Thu, Oct 26, 2023, at 09:39, wuqiang.matt wrote:
> arch_cmpxchg[64]_local() are not defined for openrisc. So implement
> them with generci_cmpxchg[64]_local, advised by Masami Hiramatsu.
>
> Closes:
> https://lore.kernel.org/linux-trace-kernel/169824660459.24340.14614817132696360531.stgit@devnote2
> Closes:
> https://lore.kernel.org/oe-kbuild-all/[email protected]
>
> Signed-off-by: wuqiang.matt <[email protected]>
I think on architectures that have actual atomics, you
generally want to define this to be the same as arch_cmpxchg()
rather than the generic version.
It depends on the relative cost of doing one atomic compared
to an irq-disable/enable pair, but everyone else went with
the former if they could. The exceptions are armv4/armv5,
sparc32 and parisc, which don't have a generic cmpxchg()
or similar operation.
You could do the thing that sparc64 and xtensa do, which
use the native cmpxchg for supported word sizes but the
generic version for 1- and 2-byte swaps, but that has its
own set of problems if you end up doing operations on both
the entire word and a sub-unit of the same thing.
Arnd
