I was at a meeting IBM had with several ISVs at
which removal of TX and CTX was discussed. The
consensus in the room seemed to be that no one
particularly cared about TX, but many cared rather strongly about CTX!
It turned out that several ISVs were using CTX
and that they realized significant benefit from
doing so. Apparently, there was more usage than I think IBM expected.
So I don't think it's accurate to think that
there was "minimal usage". I am hopeful that IBM
will reconsider in light of this input.
Note, "dual path'ing" your code applies to TX, not to CTX.
David Cole
President, ColeSoft Marketing
[email protected] (personal)
[email protected] (business)
540-456-6518 (cell)
At 4/6/2022 06:46 PM, Dan Greiner wrote:
I was as surprised no, make that shocked to
see that IBM announced the removal of
transactional-execution (TX) and
constrained-transactional-execution (CTX)
facilities in some future Z system. During the
development of the facility, it showed
significant (incredible!) performance benefits
in lock elision; it was also touted by the Java
development team for its speculative-execution characteristics.
Having been retired for over four years now, I
cannot speak to the rationale (or irrationale)
for planning on the facilities' removal. One
might speculate that the minimal usage of the
facilities did not justify the ongoing
complexity of their implementation (TX is REALLY complex).
As with any new architectural feature, it takes
quite a while before many ISVs and customers
exploit it. Having to dual-path one's code to
account for the presence or absence of such a
facility only prolongs the delay in
exploitation. Consider how long it takes for an
OS's level-set to catch up with the
ever-evolving architecture. But if TX was such a
hot feature, why wasn't its exploitation by
IBM's own software sufficient to justify the obvious benefits that it provided?
As the announcement letter said, "In some future
IBM Z hardware system family, the transactional
execution and constrained transactional
execution facility will no longer be supported."
Perhaps this ambiguity opens the possibility to
a change of heart on IBM's part if enough
customers and ISVs protest loudly enough ... but I doubt it.
As to Mr. Shaw's comment about "feeling kinda
'had' now" ... yeah, that's a polite way to put it.
