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

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Message-ID: <alpine.DEB.2.11.1511061832590.4032@nanos>
Date:	Fri, 6 Nov 2015 18:35:11 +0100 (CET)
From:	Thomas Gleixner <tglx@...utronix.de>
To:	Dan Williams <dan.j.williams@...el.com>
cc:	Ross Zwisler <ross.zwisler@...ux.intel.com>,
	Jeff Moyer <jmoyer@...hat.com>,
	linux-nvdimm <linux-nvdimm@...1.01.org>, X86 ML <x86@...nel.org>,
	Dave Chinner <david@...morbit.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Ingo Molnar <mingo@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>, Jan Kara <jack@...e.com>
Subject: Re: [PATCH 0/2] "big hammer" for DAX msync/fsync correctness

On Fri, 6 Nov 2015, Dan Williams wrote:
> On Fri, Nov 6, 2015 at 12:06 AM, Thomas Gleixner <tglx@...utronix.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
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