Re: [Xen-devel] [RFC 10/16] gic:vgic:gic-vgic: introduce non-atomic bitops

[Andrii Anisov <andrii.anisov@xxxxxxxxx>]

Hello Andre,

On 29.11.18 14:14, Andre Przywara wrote:
> Nah, please don't do this.
Sorry for making you crying looking at this code.
It's terrible, I know. It's rather an idea.

> Can you show that atomic bit ops are a
> problem? They shouldn't be expensive unless contended, also pretty
> lightweight on small systems (single cluster).
Yep, but still it is a call to a function of 10 operations instead of 
one `orr` for set_bit(). Taking in account a heavy usage of bitops in 
the old vgic code, this should benefit latency.
> But if you really think this is useful, why not go with the Linux way
> of using __set_bit to provide a non-atomic version?
> This would have the big advantage that you can replace them on a
> case-by-case base, which is much less risky than unconditionally
> replacing every (even future!) usage in the whole file.
Whatever you prefer :)

--
Sincerely,
Andrii Anisov.

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