Re: [PATCH v2 03/11] pmem: enable REQ_FUA/REQ_FLUSH handling

[Dan Williams]

On Mon, Nov 16, 2015 at 6:05 AM, Jan Kara <jack@xxxxxxx> wrote:
> On Mon 16-11-15 14:37:14, Jan Kara wrote:
[..]
> But a question: Won't it be better to do sfence + pcommit only in response
> to REQ_FLUSH request and don't do it after each write? I'm not sure how
> expensive these instructions are but in theory it could be a performance
> win, couldn't it? For filesystems this is enough wrt persistency
> guarantees...

We would need to gather the performance data...  The expectation is
that the cache flushing is more expensive than the sfence + pcommit.
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