The example that I have seen was where the customer had a linkage model for small subroutines that used a static save area and local storage after a branch at the start of the program. That's painful for small routines because a lot of the code is in the same cache line and gets hit each time you store something. If you can't change it all, it would be interesting how much can be undone by some slack space between the save area and the code to ensure it's a different cache line. And you would only have to do with the 10% of the code that makes up for 90% of the overhead.
Rob On 12 November 2016 at 05:52, Philippe Cloarec <philippe.cloa...@gmail.com> wrote: > Hi, > As you may know, there is some kind of performance issue because of > SIIS(Store Into Instruction Stream) after upgrade to a z13 machine in some > scenarios. CPU increase of 30% can be seen in some case, so it may be good > to perform to related changes to avoid issue from reoccuring. Did start to > work on this case since some time. Here we do talk of code written years > ago, hundreds of programs for which there is no time to rewrite them as > RENT, so I am interested to talk with any having some experience about > this. More generally, dealing with old even old code, I would like to > change the code beside SIIS case to improve the performance at execution > time. I mean by using newer instructions and optimizing the code to save > some CPU cycles. Did find some interesting documents but wanting to > discuss of any scenario we can think about. TTYL then. Philippe ( > philippe.cloa...@gmail.com) >
