dmcq (dmcq.delete@this.fano.co.uk) on August 21, 2022 11:36 am wrote:
> Kara (karaardalan.delete@this.gmail.com) on August 20, 2022 11:04 pm wrote:
> > rwessel (rwessel.delete@this.yahoo.com) on August 20, 2022 6:50 pm wrote:
> > > HTM on about the only platform on which it's been reasonably
> > > successfully implemented, namely Z, is going away.
> > >
> > > On page 93 of:
> > >
> > > https://www.redbooks.ibm.com/redpieces/pdfs/sg248951.pdf
> > >
> > > "Removal of support of the transactional execution and constrained transactional
> > > execution facility: In a future IBM Z hardware system family, the transactional execution
> > > and constrained transactional execution facility will no longer be supported. Users of the
> > > facility on current servers should always check the facility indications before use."
> > >
> > > So introduced on the EC12s, and still on z16, but not long for this world.
> > >
> > > IBM also removed it from Power10 a couple of years ago.
> >
> >
> > Well, ARM is just getting started with its TME lol.
> >
> > Also I remember in anandtech's deep dive of the M1 they said apple is using
> > a HTM to share threads between the big cores, so, that's something!
>
> Yes I was more than a little surprised about ARM talking about transactional memory when
> launching ARMv9. They did clean up their memory model when they found problems investigating
> it a few years ago but I think they must have got to the stage where they believe they can
> actually implement a reasonable version? Perhaps IBM have discovered a problem like ARM did?
> Or maybe they've had a better idea? Or is implementing it just too costly overall?


AFAIK, there have been no major issues with HTM on Z in the five generations it's been implemented on (although z16 experience is thin at this point). Presumably usage is too low and/or the performance gains are too limited (obviously those may be two side of the same coin). Or perhaps just too much work to implement for the gain.