Date: Wed, 17 Jun 2015 17:15:57 +0200 (CEST)
From: Thomas Gleixner <tglx@linutronix.de>
To: Andy Lutomirski <luto@amacapital.net>
cc: Dan Williams <dan.j.williams@intel.com>, Arnd Bergmann <arnd@arndb.de>,
        Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
        "H. Peter Anvin" <hpa@zytor.com>,
        Ross Zwisler <ross.zwisler@linux.intel.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Juergen Gross <jgross@suse.com>, X86 ML <x86@kernel.org>,
        Toshi Kani <toshi.kani@hp.com>,
        linux-nvdimm <linux-nvdimm@ml01.01.org>,
        Benjamin Herrenschmidt <benh@kernel.crashing.org>,
        Luis Rodriguez <mcgrof@suse.com>,
        Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        Stefan Bader <stefan.bader@canonical.com>,
        "linux-mm@kvack.org" <linux-mm@kvack.org>,
        Geert Uytterhoeven <geert@linux-m68k.org>,
        Ralf Baechle <ralf@linux-mips.org>,
        Henrique de Moraes Holschuh <hmh@hmh.eng.br>,
        Michael Ellerman <mpe@ellerman.id.au>, Tejun Heo <tj@kernel.org>,
        Paul Mackerras <paulus@samba.org>, Christoph Hellwig <hch@lst.de>
Subject: Re: [PATCH v4 6/6] arch, x86: pmem api for ensuring durability of
 persistent memory updates
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References: <20150611211354.10271.57950.stgit@dwillia2-desk3.amr.corp.intel.com> <20150611211947.10271.80768.stgit@dwillia2-desk3.amr.corp.intel.com> <CALCETrXXYyjKHi1ajR6aescmjSo5eds=5g_byWpzBRbBNdsgRQ@mail.gmail.com>
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On Wed, 17 Jun 2015, Andy Lutomirski wrote:
> On Thu, Jun 11, 2015 at 2:19 PM, Dan Williams <dan.j.williams@intel.com> wrote:
> > +static inline void arch_sync_pmem(void)
> > +{
> > +       wmb();
> > +       pcommit_sfence();
> > +}
> 
> This function is non-intuitive to me.  It's really "arch-specific sync
> pmem after one or more copies using arch_memcpy_to_pmem".  If normal
> stores or memcpy to non-WC memory is used instead, then it's
> insufficient if the memory is WB and it's unnecessarily slow if the
> memory is WT or UC (the first sfence isn't needed).
> 
> I would change the name and add documentation.  I'd also add a comment
> about the wmb() being an SFENCE to flush pending non-temporal writes.

Not "I'd also add ...".

Documentation of memory barriers are mandatory.

Thanks,

	tglx
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