Re: [PATCH 0/2] "big hammer" for DAX msync/fsync correctness

From	Thomas Gleixner <tglx@linutronix.de>
Newsgroups	linux.kernel
Subject	Re: [PATCH 0/2] "big hammer" for DAX msync/fsync correctness
Date	2015-11-07 08:00 +0100
Message-ID	<qs5DI-7fZ-5@gated-at.bofh.it> (permalink)
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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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Thread

Re: [PATCH 0/2] "big hammer" for DAX msync/fsync correctness Dan Williams <dan.j.williams@intel.com> - 2015-11-06 01:00 +0100
  Re: [PATCH 0/2] "big hammer" for DAX msync/fsync correctness Thomas Gleixner <tglx@linutronix.de> - 2015-11-06 09:10 +0100
    Re: [PATCH 0/2] "big hammer" for DAX msync/fsync correctness Dan Williams <dan.j.williams@intel.com> - 2015-11-06 17:10 +0100
      Re: [PATCH 0/2] "big hammer" for DAX msync/fsync correctness Thomas Gleixner <tglx@linutronix.de> - 2015-11-06 18:40 +0100
        Re: [PATCH 0/2] "big hammer" for DAX msync/fsync correctness Dan Williams <dan.j.williams@intel.com> - 2015-11-07 00:20 +0100
          Re: [PATCH 0/2] "big hammer" for DAX msync/fsync correctness "H. Peter Anvin" <hpa@zytor.com> - 2015-11-07 02:00 +0100
            Re: [PATCH 0/2] "big hammer" for DAX msync/fsync correctness Thomas Gleixner <tglx@linutronix.de> - 2015-11-07 08:00 +0100
              Re: [PATCH 0/2] "big hammer" for DAX msync/fsync correctness Dan Williams <dan.j.williams@intel.com> - 2015-11-07 09:20 +0100
                Re: [PATCH 0/2] "big hammer" for DAX msync/fsync correctness Thomas Gleixner <tglx@linutronix.de> - 2015-11-07 09:50 +0100
                Re: [PATCH 0/2] "big hammer" for DAX msync/fsync correctness Dan Williams <dan.j.williams@intel.com> - 2015-11-07 10:10 +0100
                Re: [PATCH 0/2] "big hammer" for DAX msync/fsync correctness Thomas Gleixner <tglx@linutronix.de> - 2015-11-07 10:30 +0100
  Re: [PATCH 0/2] "big hammer" for DAX msync/fsync correctness "H. Peter Anvin" <hpa@zytor.com> - 2015-11-06 21:30 +0100

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