On Fri, 6 Nov 2015, H. Peter Anvin wrote:
> On 11/06/15 15:17, Dan Williams wrote:
> >>
> >> Is it really required to do that on all cpus?
> >
> > I believe it is, but I'll double check.
> >
>
> It's required on all CPUs on which the DAX memory may have been dirtied.
> This is similar to the way we flush TLBs.
Right. And that's exactly the problem: "may have been dirtied"
If DAX is used on 50% of the CPUs and the other 50% are plumming away
happily in user space or run low latency RT tasks w/o ever touching
it, then having an unconditional flush on ALL CPUs is just wrong
because you penalize the uninvolved cores with a completely pointless
SMP function call and drain their caches.
Thanks,
tglx
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