Re: [Qemu-devel] [PATCH v3 17/27] tcg-ppc64: Implement bswap64

[Richard Henderson]

On 2013-04-02 07:41, Alexander Graf wrote:
> > On 2013-04-01 23:34, Alexander Graf wrote:
> > > Is this faster than a load/store with std/ldbrx?
> >
> > Hmm.  Almost certainly not.  And since we've got stack space
> > allocated for function calls, we've got scratch space to do it in.
> >
> > Probably similar for bswap32 too, eh?
>
> Depends - memory load/store doesn't come for free and bswap32 is quite short.
>
> > I'll do a tiny bit o benchmarking for power7.
>
> Cool, thanks a bunch :)

Heh.  "Almost certainly not" indeed.  Unless I've made some silly mistake,
going through memory stalls badly.  No store buffer forwarding on power7?

With the following test case, time reports:

f1              2.967s
f2              8.930s
f3              7.071s
f4              7.166s

And note that f4 is a normal store/load pair, trying to determine what the
store buffer forwarding delay might be.


r~

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