Re: [PATCH 2/2] rwsem: do optimistic spinning for writer lock acquisition

[Tim Chen <tim.c.chen@linux.intel.com>]

On Mon, 2013-06-24 at 10:46 +0200, Peter Zijlstra wrote:
> On Fri, Jun 21, 2013 at 04:51:40PM -0700, Tim Chen wrote:
> > Introduce in this patch optimistic spinning for writer lock
> > acquisition in read write semaphore.  The logic is
> > similar to the optimistic spinning in mutex but without
> > the MCS lock queueing of the spinner.  This provides a
> > better chance for a writer to acquire the lock before
> > being we block it and put it to sleep.
> > 
> > Disabling of pre-emption during optimistic spinning
> > was suggested by Davidlohr Bueso.  It
> > improved performance of aim7 for his test suite.
> > 
> > Combined with the patch to avoid unnecesary cmpxchg,
> > in testing by Davidlohr Bueso on aim7 workloads
> > on 8 socket 80 cores system, he saw improvements of
> > alltests (+14.5%), custom (+17%), disk (+11%), high_systime
> > (+5%), shared (+15%) and short (+4%), most of them after around 500
> > users when he implemented i_mmap as rwsem.
> > 
> > Signed-off-by: Tim Chen <tim.c.chen@linux.intel.com>
> > ---
> >  Makefile              |    2 +-
> >  include/linux/rwsem.h |    3 +
> >  init/Kconfig          |    9 +++
> >  kernel/rwsem.c        |   29 +++++++++-
> >  lib/rwsem.c           |  148 +++++++++++++++++++++++++++++++++++++++++++++----
> >  5 files changed, 178 insertions(+), 13 deletions(-)
> > 
> > diff --git a/Makefile b/Makefile
> > index 49aa84b..7d1ef64 100644
> > --- a/Makefile
> > +++ b/Makefile
> > @@ -1,7 +1,7 @@
> >  VERSION = 3
> >  PATCHLEVEL = 10
> >  SUBLEVEL = 0
> > -EXTRAVERSION = -rc4
> > +EXTRAVERSION = -rc4-optspin4
> >  NAME = Unicycling Gorilla
> >  
> >  # *DOCUMENTATION*
> 
> I'm fairly sure we don't want to commit this hunk ;-)

Fat fingers.  Thanks for catching.

Tim