Related to this, I watched a talk by Matt Godbolt (of Compiler Explorer https://godbolt.org/ fame) and, although it's based on x64 examples, the principles are much the same. I've seen some of what Z boxes can do and it's obvious IBM is still improving speed and efficiency. FTW https://www.youtube.com/watch?v=-HNpim5x-IE
Who was it who used wear a "nanosecond" (around 1 foot) as part of a necklace, then remind people electrical signals run a bit slower than the speed of light in a vacuum? And every time I hear that a divide instruction can take up to e.g. 80 cycles, while the same processor can pipeline several additions in parallel per cycle, I am surprised again. Roops On Thu, 17 Apr 2025, 08:56 P H, < [email protected]> wrote: > Most of the key points have already been mentioned by others. Important > thing to remember is that GHz on their own don't mean much. > > A bit of history: > > zEC12 was 5.5 GHz, z13 went down to 5.0 GHz, z14 5.2 GHz, z15 5.2 GHz, z16 > 5.2 GHz, z17 5.5 GHZ > > At the time of the z13 announcement there was a lot discussion as to how > going from 5.5 GHz to 5.0 GHz gave a better 'performance'. > > It has to do with the total System design and not just GHz. Below are some > points which were made at that time and are still relevant etc. > > > > §Why the overall CPU frequency evolution approach is changing ? > ̶Consistent frequency growth in the past decade > •from hundreds of MHz to GHz > ̶Core frequency has been reduced in the past couple of years̶ > Designing chips for better performance > ̶Limits are imposed by physics, technology or economics > ̶Limitations in core frequency drives improvements in different dimensions > ̶Different processor architectures have different issues with core > frequency increase > Physical limitations > ̶Speed of signal lines form one end to the other on a chip > ̶Power consumption and heat dissipation (cooling) > ̶How many memory elements (caches) can be within a given latency from the > CPU > Physical limitations force the designers to make trade-offs > ̶“Shrinking” a processor chip > •pro: Faster due to shorter signal lines > •con: Reduced area for heat dissipation > ̶Lowering the processor voltages would make transistors switch quicker > •pro: Frequency could then be increased > •con: Current also increases creating more heat > §Sounds easy.. but… it causes serious problems with cooling > > GHz is not the only dimension that matters > ̶z Systems focus is on balanced system design across > many factors: > •Frequency, pipeline, efficiency, energy efficiency, cache/memory > design and I/O design > •Greater logic density, power density, wire-ability. All permits more > cores per chip, larger cache, additional execution units/circuits, > addition of SMT and SIMD on each core. > System performance is not linear with frequency > ̶Need to use LSPR and z Systems capacity planning tools for real client / > workload sizing > z Systems leverages advanced technologies to get the most out of chips’ > design > ̶Low latency pipelines > ̶Dense packaging with proper cooling which yields more power-efficient > operation > ̶Consistent performance at high utilization > The IBM z13 > ̶z13 is a significant change from zBC12 > ̶Processor speed measured in instructions per second (for a given > workload) has increased as compared to the zBC12 due to: > •Wider pipeline (up to six instructions per cycle) > •Enhanced branch prediction > •Optimized resolution of dependencies between instructions. > •Cache size and design enhancements > Processor frequency increase > > > > > ________________________________ > From: IBM Mainframe Discussion List <[email protected]> on behalf > of Charles Mills <[email protected]> > Sent: 16 April 2025 17:11 > To: [email protected] <[email protected]> > Subject: Re: z17 > > If you Google <why processors not getting faster> you will see Reddit and > Quora threads going back to about 2010 covering just this topic. I was > going to post a link or two but no one article is perfect. They are all > oriented (of course!) toward the Intel 486/Pentium/etc. family but chips is > chips, more or less. The same physics applies. So if you wish, do your own > Googling. > > The detail reasons have been posted by others. Fast cycle time = more > power = more heat = big problem on a small piece of real estate. Size > (length of electrical signal), heat dissipation and cycle speed work > against each other. > > Processors actually HAVE been getting faster. The chips are getting faster > not in terms of cycle speed but rather in terms of greater parallelism and > new instructions that do more in a single cycle. Same for Intel, by the way. > > The "new instructions" part is why IBM puts so much emphasis on > recompiling (or re-sort-of-compiling with the COBOL ABO) existing COBOL > applications. > > The various "do X on condition" instructions (where X is load, store, > etc.) that came along a couple of arch levels ago are a great example. They > replace (if you code them in HLASM, or let a compiler generate them) the > classic compare/branch/load or store sequence. Branches are a parallelism > killer because they make the chip consider two different paths. Conditional > instructions are not. The vector instructions are a great example of single > instructions that do more with their cycles than their predecessors did. > > Charles > > On Wed, 16 Apr 2025 08:29:43 -0500, Steve Beaver <[email protected]> > wrote: > > >What I am disappointed in is the CP's have not gone faster than 5.5 Ghz. > > > >I know the z17 is an evolution, but why have they not gotten faster? > > ---------------------------------------------------------------------- > For IBM-MAIN subscribe / signoff / archive access instructions, > send email to [email protected] with the message: INFO IBM-MAIN > > ---------------------------------------------------------------------- > For IBM-MAIN subscribe / signoff / archive access instructions, > send email to [email protected] with the message: INFO IBM-MAIN > ---------------------------------------------------------------------- For IBM-MAIN subscribe / signoff / archive access instructions, send email to [email protected] with the message: INFO IBM-MAIN
