[openib-general] mwrite64 - need for uar object in access layer

[Michael S. Tsirkin]

Quoting r. Roland Dreier (roland at topspin.com) "Re: [openib-general] mwrite64 - need for uar object in access layer":
>     Troy> How does just using the floating point unit compare the the
>     Troy> SSE codepath? In a past life I had to get a flash driver for
>     Troy> a 32 bit PPC board working that *had* to have 64 bit access
>     Troy> to flash.
> 
> It's a pretty huge loss, because saving/restoring the FPU state
> requires writing/reading something like 170 bytes.  With SSE we can
> just save the 8 bytes of XMM register that we actually use.  Even so
> I'm not convinced SSE is a win over just using a lock because saving
> CR0 is so expensive.
> 
> As I said, I'd be curious to see benchmarks of other approaches.  I
> think there's definitely room for improvement if someone is interested
> in working on this.
> 

Well, profiling is always nice but hard to do.
But just doing a two word write is clearly a win, no?

MST