> Does anyone have experience running zLinux in an LPAR which > has multiple > CPUs defined? We have experienced negative performance > characteristics > with Intel Linux versions (RedHat, SUSSE) when the Intel machine had 4 > processors. We were wondering if the same performance > degradations appear > on the mainframe.
There is an impact (must be), but it is not as severe (in our observation) as the impact on Intel boxes. The IBM processor designers have done good work in keeping the performance curve fairly linear (the dropoff is really up in the high end of the curve, in the 12-16 physical engine range). Our testing is under VM, but I'd expect similar behavior for LPAR as well. Which Linux kernel release did you do your Intel testing on? 2.2 had a practical limitation of 4 processors for actually doing useful work; recent 2.4 are fairly efficient up to 8, and the preliminary work with 2.6 seems to indicate that 16 is easily doable, and more may be useful for certain problems (not general purpose). We have a couple virtual machines with 16 CPUs defined that seem to work ok for heavily-threaded stuff. It also depends a lot on your application and how it dispatches work. Things using NPTL seem to do better in MP situations. IBM has some performance stuff they show in presentations on 16-way LPARs; dunno if they have that publically available. -- db ---------------------------------------------------------------------- For LINUX-390 subscribe / signoff / archive access instructions, send email to [EMAIL PROTECTED] with the message: INFO LINUX-390 or visit http://www.marist.edu/htbin/wlvindex?LINUX-390
