Re: [PATCH 1/5] locking: Introduce range reader/writer lock

[Davidlohr Bueso]

On Wed, 29 Mar 2017, Kirill A. Shutemov wrote:

> On Wed, Mar 29, 2017 at 08:31:33AM -0700, Davidlohr Bueso wrote:
> > On Wed, 29 Mar 2017, Laurent Dufour wrote:
> >
> > > On 28/03/2017 18:58, Kirill A. Shutemov wrote:
> > > > On Tue, Mar 28, 2017 at 09:39:18AM -0700, Davidlohr Bueso wrote:
> > > > > I'll wait to see if there are any more concerns and send a v2 with your corrections.
> > > >
> > > > Have you tried drop-in replacement of mmap_sem with full range lock?
> > > > It would be interesting to see performance implication for this.
> > > >
> > >
> > > I've a patch that replace the mmap_sem with a full range lock, it seems
> > > to work fine for x86 and ppc64 for now. I'll send it soon.
> > > But I didn't yet check for performance. What is the best way to that ?
> >
> > I expect performance to take a measurable hit if we simply use full range
> > lock as a drop in replacement. My rwsem vs range lock measurements were
> > done with this in mind. We only win with range locks when improving the
> > level of parallelism.
>
> It would be hard sell if we would see performance degradation simple
> single-threaded workload.

Yeah, that's why I included very low contention in the lock comparison.
Deltas are very much within the noise region, it is with high contention
where things go south performance wise.