Messages in this thread | | | Date | Sat, 7 Nov 2015 07:50:16 +0100 (CET) | From | Thomas Gleixner <> | Subject | Re: [PATCH 0/2] "big hammer" for DAX msync/fsync correctness |
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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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