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Re: [PATCH v2 0/5] Convert Sparc to atomic optabs
On 11/30/2011 09:44 AM, David Miller wrote:
> Linux originally did RMO but I killed that several years ago, no
> new chips are implementing RMO and this means all the necessary
> membar instructions are nothing but pure overhead.
Well, you've now got the option for -mmemory-model=sc to omit every last one.
> Solaris always ran userspace in TSO as far as I remember.
Ok.
> Your change will leave FreeBSD and NetBSD with the RMO setting, and
> both of them run userland in TSO as well.
Eh. It'll be easy enough for a bsd maintainer to update if they like.
> BTW, Linux has a "memory_ordering" system call where you can change
> the PSTATE_MM setting to whatever memory model you like. I suppose
> Solaris has something similar.
Interesting, but...
> So one thing to consider doing is, if there is some doubt, to set
> it explicitly to TSO in some crt code.
... easier to keep the RMO/PSO default in that case.
r~