TSX lock elision for glibc v12

[Torvald Riegel]

On Fri, 2013-06-21 at 14:59 +0200, Andi Kleen wrote:
> > To clarify, with my approach, the ONLY cases where applications would
> > get the no-elision penalty is when they explicitly create a
> > normal-type mutex or call pthread_mutexattr_settype without using the
> > new version of pthread.h. Using PTHREAD_MUTEX_INITIALIZER or
> > pthread_mutex_init without calling pthread_mutexattr_settype on the
> > attribute (or with a null attribute) would result in a default-type
> > mutex and thus would allow elision.
> > 
> > I think this approach would make even Andi happy. :-)
> 
> To make sure I understand your approach correctly:
> 
> - Have a new ABI version of pthread_mutexattr_settype()
> - Define a new PTHREAD_MUTEX_NORMAL enum
> - The new ABI version of settype() would understand a
> new different value for PTHREAD_MUTEX_NORMAL and if that
> value is set, set either an additional disable elision
> or disable nested non trylock elision flag.
> It would enable elision for passing 0.
> - The old ABI version of settype would always set the 
> no elision or no nested elision flags for the current 0 value
> (aka TIMED/NORMAL/DEFAULT)
> - Just using 0 in an initializer will not set any of the
> additional flags that disable elision.
> 
> Is that correct?

That's not what I have in mind at least.  See the 2.18 discussion
thread.