Re: [RFC PATCH-tip 6/6] xfs: Enable reader optimistic spinning for DAX inodes

[Waiman Long <waiman.long@xxxxxxx>]

On 06/14/2016 02:24 PM, Christoph Hellwig wrote:
> On Tue, Jun 14, 2016 at 02:12:39PM -0400, Waiman Long wrote:
> > This patch enables reader optimistic spinning for inodes that are
> > under a DAX-based mount point.
> >
> > On a 4-socket Haswell machine running on a 4.7-rc1 tip-based kernel,
> > the fio test with multithreaded randrw and randwrite tests on the
> > same file on a XFS partition on top of a NVDIMM with DAX were run,
> > the aggregated bandwidths before and after the patch were as follows:
> And why is this specific to DAX?  Many I/O operations already never
> got out to disk, and ilock is mostly held for operations that have
> nothing to do with disk I/O.
It is just a showcase for the rwsem change. We can certainly have more 
use cases.
Cheers,
Longman