Just to provide some perspective on the value of SMT-2, critical system functions are SMT-2 -- no choice. For example SAP runs SMT-2 on z15 (I haven't checked for earlier models as we have z15). So SMT-2 is "so bad" that it is always used for one of the key mainframe differentiators over other architectures :) That said, performance is always a balance between throughput, latency and path length ... SMT-2 can affect all 3 in complex ways. And measuring it can be difficult, still a black art. I'd claim that for the majority of transactional mainframe workloads using SMT-2 for zIIPs is optimal.
On Tue, Sep 5, 2023 at 9:19 PM Scott Chapman < 000003fffd029d68-dmarc-requ...@listserv.ua.edu> wrote: > It's more complicated than that. Although I would agree that if an LPAR > has only a single zIIP, likely SMT would be a good idea. But B is not true > for intervals that people usually consider when looking at utilization > levels because at the level of dispatch intervals, it's much more likely > there's at least some intervals where the zIIPs are 100% busy. It really > depends on arrival patterns and how much you care about very short > transactions that may be running on the zIIPs. > > On Mon, 4 Sep 2023 20:10:31 +1000, Andrew Rowley < > and...@blackhillsoftware.com> wrote: > > >The current situation sounds like SMT-2 should only be used if you > > > >a) have a single zIIP > > > >or b) are running your zIIPs consistently 100% busy > > > >and for b) you need to turn it off when the workload reduces? > > > >-- > >Andrew Rowley > >Black Hill Software > > > >---------------------------------------------------------------------- > >For IBM-MAIN subscribe / signoff / archive access instructions, > >send email to lists...@listserv.ua.edu with the message: INFO IBM-MAIN > > ---------------------------------------------------------------------- > For IBM-MAIN subscribe / signoff / archive access instructions, > send email to lists...@listserv.ua.edu with the message: INFO IBM-MAIN > ---------------------------------------------------------------------- For IBM-MAIN subscribe / signoff / archive access instructions, send email to lists...@listserv.ua.edu with the message: INFO IBM-MAIN
