Editing ibm/microarchitectures/z15

{{ibm title|z15|arch}}
{{microarchitecture
|atype=CPU
|name=z15
|designer=IBM
|manufacturer=GlobalFoundries
|introduction=September 12, 2019
|process=14 nm
|cores=9
|cores 2=10
|cores 3=11
|cores 4=12
|type=Superscalar
|type 2=Pipelined
|oooe=Yes
|speculative=Yes
|renaming=Yes
|stages=17
|decode=6-way
|isa=z/Architecture
|l1i=128 KiB
|l1i per=core
|l1i desc=8-way set associative
|l1d=128 KiB
|l1d per=core
|l1d desc=8-way set associative
|l3=256 MiB
|l3 per=chip
|l3 desc=32-way set associative
|l4=960 MiB
|l4 per=drawer
|l4 desc=60-way set associative
|predecessor=z14
|predecessor link=ibm/microarchitectures/z14
}}
'''z15''' is the successor to the {{\\|z14}}, a [[14 nm]] [[z/Architecture]] mainframe microarchitecture designed by [[IBM]] and introduced in 2019.


==Process Technology==
IBM fabricates its z15 microprocessors and system controllers on [[GlobalFoundries]]'s [[14 nm process|14 nm]] (14HP) [[FinFET]] [[Silicon-On-Insulator]] (SOI) process featuring highly-dense [[deep trench structures]] used for high-density [[eDRAM]].

== Release Dates ==
The z15 was launched by IBM on September 12, 2019. General availability of the z15 mainframe started September 23.

== Architecture ==
=== Key changes from {{\\|z14}} ===
* Mainframe
** Up to 190-way multiprocessing (from 170-way)
** Less CPs per drawer (4, down from 6)
** Less CPs per logical cluster (2, down from 3)
** 1 more drawer (5, up from 4)
** 0-12 PCIe+ I/O drawers (up from 0-5 drawers)
** Rack
*** standard 19" racks (from 24-inch racks)
*** 1-4 frame configs (up from only 2-frame configs)
*** rear only I/O and power connections (from front & rear)


* Central Processor (CP)
** 2 more cores (12, up from 10)
** Core
*** 10-13% higher IPC (IBM claim)
*** Front-end
**** Improved [[branch predictor]]
***** New [[TAGE predictor]]
***** BTB pre-buffer (BTBp) replaced by a simpler write buffer
****** single double-bandwidth port (two independentread ports)
***** 2x larger L1 BTB (8 sets of 2K rows, up from 4 sets of 2K rows) 
*** Back-end
**** Larger GCT (60 groups, up from 48 groups)
***** Wider retire (12 instructions/cycle, up from 10)
**** Larger Issue Queues (2 x 36-entry, up from 2 x 30-entry)
**** 2x larger mapper (128-entry, up from 64-entry)
**** Larger integer physical register files (???, up from 120 entries)
**** Larger vector physical register files (???, up from 127 entries)
*** Execution engine
**** Wider execute (12 instructions/cycle, up from 10)
**** New Modulo Arithmetic (MA) unit
*** Memory subsystem
**** 2x larger [[L2]] [[instruction cache]] (4 MiB, up from 2 MiB)
**** 2x larger 2 GiB pages STLB (256-entry, up from 64 entries)
** Shared L3
*** 2x larger [[L3]] (256 MiB, up from 128 MiB)
** I/O
*** GX Bus removed
*** X Bus removed (2 interface, down from 3)
*** New PCIe Gen interface (3 interfaces, up from 2)
** Memory
*** Larger memory support (40 TiB, up from 32 TiB)
** New integration
*** Nest Acceleration Unit (NXU)


* System Controller (SC)
** 1.4x Larger L4 cache (960 MiB, up from 672 MiB)
*** Non-exclusive (from inclusive)

=== Block Diagram ===
==== CP Chip ====
:[[File:z15 chip block diagram.svg|800px]]

==== Individual core ====
:[[File:z15 block diagram.svg|900px]]

=== Memory Hierarchy ===
The z15 features a memory structure very similar to the {{\\|z14}}.

* Cache:
** L1 instruction cache
*** 128 KiB, 8-way set associative
*** 64 sets, 256 B line size
** L1 data cache
*** 128 KiB, 8-way set associative
*** 64 sets, 256 B line size
** L2 instruction cache
*** 4 MiB, 8-way set associative
*** 2K sets, 256 B line size
** L2 data cache
*** 4 MiB, 8-way set associative
*** 2K sets, 256 B line size
** L3 cache
*** 256 MiB, 32-way set associative
*** 32K sets, 256 B line size
** L4 cache (off-chip, on the SC chip)
*** 960 MiB, 40-way set associative
*** 64K sets, 256 B line size
*** Non-exclusive (almost always inclusive, but not strictly)
** System Memory
*** Up to 40 TiB
*** Up 5 DIMMs (one DIMM per channel)
**** 5th DIMM for [[Redundant Array of Independent Memory]] (RAIM) (Note: No non-RAIM option)
**** 32, 64, 128, 256 and 512 GiB DIMMs

* TLBs:
** ITLB
*** 4 sets x 128 entries
** DTLB
*** 4 KiB pages
**** 4 sets x 256 entries
*** 1 MiB pages
**** 4 sets x 128 entries
*** 2 GiB pages
**** 2 sets x 32 entries
** STLB
*** 4 KiB pages
**** 6K entries
*** 2 GiB pages
**** 256 entries
*** Segment Table
**** 8 sets x 256 entries
*** Page Table
**** 8 sets x 256 entries

== Overview ==
Introduced in early September 2019, the z15 mainframe is the successor to the {{\\|z14}}. The z15 is designed to improve both single-thread and multi-core performance as well as introduce better data security features for pervasive encryption through new hardware acceleration. 

{{work-in-progress}}


=== Mainframe ===
The z15 mainframe has changed from the z14 in a number of important ways. IBM switched from a 24-inch to standard 19-inch rack chassis, meaning they can now be incorporated into standard data center aisles. For this, IBM provides new options for hot and cold aisle configurations. Unlike the last few generations which came in only 2-frame options, the new z15 is intended to scale from one to four frames depending on the desired configuration. Additionally, the z15 comes with 1 to 5 CPC drawers.

==== Models ====
The z15 comes in a single model - T01. There are 5 feature codes.

{| class="wikitable"
|-
! colspan="9" | z15 T01 Configurations
|-
! Feature<br>Code !! Feature<br>Name !! CPC Drawers !! Core !! Spare Cores !! SAPs !! Memory !! Frequency !! Max PCIe<br>fanout
|-
| 0655 || Max34 || 1 || 34 || 2 || 4 || 512 GiB - 7.75 TiB || 5.2 GHz || 12
|-
| 0656 || Max71 || 2 || 71 || 2 || 8 || 512 GiB - 15.75 TiB || 5.2 GHz || 24
|-
| 0657 || Max108 || 3 || 108 || 2 || 12 || 512 GiB - 23.75 TiB || 5.2 GHz || 36
|-
| 0658 || Max145 || 4 || 145 || 2 || 16 || 512 GiB - 31.75 TiB || 5.2 GHz || 48 
|-
| 0659 || Max190 || 5 || 190 || 2 || 22 || 512 GiB - 39.75 TiB || 5.2 GHz || 60
|}

Note that the z15 reserves a fixed amount of 256 GiB (0.25 TiB) for the hardware system area (HSA).

==== Frames ====
The z15 supports anywhere from one to four frames. The frames are labeled Z, A, B, and C.

{{expand section}}

== System ==
{{empty section}}

=== Drawer ===
{{empty section}}

=== Hardware system area (HSA) ===
{{empty section}}

== Central Processor ==
{{empty section}}
=== Core ===
{{empty section}}

== Die ==
=== Central Processor (CP) Chip ===
* [[14 nm process|14HP FinFET on SOI]]
** 17 metal layers
* 9,200,000,000 transistors
* 5.2 GHz
* 12 cores
* Die size
** 25.3 mm x 27.5 mm
** 695.75 mm²


:[[File:z15_cp_floorplan.png|class=wikichip_ogimage|500px]]

==== Core ====

:[[File:z15 core floorplan.png|600px]]

=== System Controller (SC) Chip ===
* [[14 nm process|14HP FinFET on SOI]]
** 17 metal layers
* 12,200,000,000 transistors
** ~20,000 C4s
** 13.5 miles of signal wire
* 960 MiB shared [[eDRAM]] [[L4 cache]].
* Die size
** 25.3 mm x 27.5 mm
** 695.75 mm²


:[[File:z15 sc floorplan.png|500px]]
codename	z15 +
core count	12 +, 9 +, 10 + and 11 +
designer	IBM +
first launched	September 12, 2019 +
full page name	ibm/microarchitectures/z15 +
instance of	microarchitecture +
instruction set architecture	z/Architecture +
manufacturer	GlobalFoundries +
microarchitecture type	CPU +
name	z15 +
pipeline stages	17 +
process	14 nm (0.014 μm, 1.4e-5 mm) +