>I wrote: > > > But if the distributors are only shipping 64-bit kernels, then '-m31' > > > still does not completely answer the question about 31-bit performance. > > > The rest of Linux will be running 64-bit, skewing the results.
> 64-bit Linux kernel will have more 64-bit concerns (and may incur > more overhead) than the same 31-bit program running on a 31-bit > Linux kernel. IFF THAT IS CORRECT, then there continues to be > value in the 31-bit kernel. >Then Ivan wrote: > > Not necessarily. Granted, the process will be running in z/Architecture > > mode, no matter what, but the instructions used will be 31 bit only and > > executing in a 31 bit addressing mode. It all depends on the cost of > > executing 31 bit instructions in z/Architecture (aka s390x) vs executing > > 31 bit instructions in ESA/390 mode (aka s390). > There may be some difference there, true. > I don't believe that was the concern of the original poster > or of the intervening contributions I have read. A 31-bit program running on a 31-bit Linux kernel will be faster than the 64-bit pendant running on a 64-bit kernel, if there is n o benefit of the bigger address space. I brought up the '-m31' compile option for user programs to show an opportunity to diminish the 64-bit overhead at least in user space. The performance of such a 31-bit program running on a 64-bit Linux will be somewhere in-between a pure 31-bit or 64-bit solution. And given the situation that the recent distributions are only available as 64-bit flavor the question is 'Do I stay with my old 31-bit kernel version or am I interested in the new features and security of a current kernel and all the other enhancements?" Think of support for new hardware. Are new versions of software in a newer distribution interesting because of new functions, better performance, better cooperation of z/VM and Linux? Mit freundlichen Gruessen/Regards Mario Held System performance engineer IBM Germany Lab, Boeblingen ---------------------------------------------------------------------- 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
