Re: [PATCH 3/6] x86, pmem: add PMEM API for persistent memory

[Ross Zwisler <zwisler@gmail.com>]

On Thu, 2015-05-28 at 21:19 -0700, H. Peter Anvin wrote:
> On 05/28/2015 05:02 PM, Dan Williams wrote:
> > 
> > Hmm, yes, but I believe Ross (on vacation now) was following the
> > precedent set by commit cd8ddf1a2800 "x86: clflush_page_range needs
> > mfence" whereby the api handles all necessary fencing internally.
> > Shall we introduce something like __unordered_clflush_cache_range()
> > for arch_persistent_flush() to use with the understanding it will 
> > be
> > following up with the wmb() in arch_persistent_sync()?
> > 
> 
> Are we ever going to have arch_persistent_sync() without
> arch_persistent_flush()?
> 
> However, thinking about it, it would be more efficient to do all 
> flushes
> first and then have a single barrier.

Yep, we have arch_persistent_sync() without arch_persistent_flush() in
both our PMEM and ND_BLK write paths.  These use arch_persistent_copy() to get NT stores, so they don't need to manually flush/write-back 
before doing a persistent_sync().