Re: [RFC] perf: fix building for ARCv1

[Vineet Gupta]

On Monday 19 October 2015 11:20 AM, Andi Kleen wrote:
> Vineet Gupta <Vineet.Gupta1@xxxxxxxxxxxx> writes:
>> But this user space - so IMHO UP/SMP doesn't matter and we can't simulate them in
>> C just by itself.
> It matters when you access the perf ring buffer which is updated by kernel.

That's part of the problem. The issue is with atomic_* APIs proliferation in perf
user space code which assumes native atomix r-m-w support which is not always
true. So I think we still need a feature detection mechanism and if absent leave
the ball in arch court by calling arch_atomic_* which can use creative or half
working measures so perf will work to some extent atleast and not bomb outright.

Also can u please elaborate a bit on "simulate them in C" - u mean just simple
unprotected LD, OP, ST or do u fancy usage of futex etc?

> Also perf is now multi threaded to some degree.


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