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Date: Fri, 6 Nov 2015 18:35:11 +0100 (CET)
From: Thomas Gleixner <tglx@linutronix.de>
To: Dan Williams <dan.j.williams@intel.com>
cc: Ross Zwisler <ross.zwisler@linux.intel.com>,
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        Ingo Molnar <mingo@redhat.com>, "H. Peter Anvin" <hpa@zytor.com>,
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Subject: Re: [PATCH 0/2] "big hammer" for DAX msync/fsync correctness
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On Fri, 6 Nov 2015, Dan Williams wrote:
> On Fri, Nov 6, 2015 at 12:06 AM, Thomas Gleixner <tglx@linutronix.de> wrote:
> > Just for the record. Such a flush mechanism with
> >
> >      on_each_cpu()
> >         wbinvd()
> >         ...
> >
> > will make that stuff completely unusable on Real-Time systems. We've
> > been there with the big hammer approach of the intel graphics
> > driver.
> 
> Noted.  This means RT systems either need to disable DAX or avoid
> fsync.  Yes, this is a wart, but not an unexpected one in a first
> generation persistent memory platform.

And it's not just only RT. The folks who are aiming for 100%
undisturbed user space (NOHZ_FULL) will be massively unhappy about
that as well.

Is it really required to do that on all cpus?

Thanks,

	tglx