F37 proposal: z13 as the Baseline for IBM Z Hardware (Self-Contained Change proposal)

[Ben Cotton]

https://fedoraproject.org/wiki/Changes/z13BaselineForIBMZ

This document represents a proposed Change. As part of the Changes
process, proposals are publicly announced in order to receive
community feedback. This proposal will only be implemented if approved
by the Fedora Engineering Steering Committee.

== Summary ==
Move the minimal architecture level for IBM Z hardware (the s390x
architecture) to z13 to benefit from the new features and better
performance in the newer CPU.

== Owner ==
* Name: [[User:sharkcz| Dan Horák]]
* Email: <sharkcz(a)fedoraproject.org&gt;


== Detailed Description ==
Moving the minimal architecture level for IBM Z hardware (the s390x
architecture) to z13 allows us to benefit from the new features and
better performance in the newer CPU. The current minimum at zEC12 is
targeting hardware that has been already obsoleted by the vendor. All
Fedora infrastructure is already using the latest z15 hardware
(builders and co and also our public resources for developers). But we
still want to be able to use existing z13 and z14 hardware. Also the
TCG (full-system/non-KVM) emulation in QEMU already allows running
distros built with z13 as the baseline architecture. This change means
updating the defaults in gcc and the build flags and in the kernel.


== Benefit to Fedora ==
The primary benefit is being able to exploit vector instructions by
default, which should increase performance. Plus take advantage of
other architectural improvements.


== Scope ==
* Proposal owners:
** update the minimal hardware level in the kernel config to z13
([https://gitlab.com/cki-project/kernel-ark/-/merge_requests/1907
MR#1907])
** set default compiler flags to <tt>-march=z13 -mtune=z14</tt> in
<tt>redhat-rpm-config</tt>
([https://src.fedoraproject.org/rpms/redhat-rpm-config/pull-request/207
PR#207]) and <tt>gcc</tt>
([https://src.fedoraproject.org/rpms/gcc/pull-request/25 PR#25])

* Other developers:
* Release engineering:
* Policies and guidelines: N/A (not needed for this Change)
* Trademark approval: N/A (not needed for this Change)
* Alignment with Objectives:


== Upgrade/compatibility impact ==
Users with hardware older than z13 should stick with F-36 or older release.


== How To Test ==
You shouldn't be able to start Fedora Linux 37 on system older than z13.


== User Experience ==
The primary difference will be in the availability of the vector
instructions and as a result better performance.

== Dependencies ==


== Contingency Plan ==
* Contingency mechanism: (What to do?  Who will do it?) N/A (not a
System Wide Change)
* Contingency deadline: N/A (not a System Wide Change)
* Blocks release? N/A (not a System Wide Change), Yes/No


== Documentation ==
N/A (not a System Wide Change)

== Release Notes ==
Starting with Fedora Linux 37 the minimal hardware level for the s390x
architecture has been updated to z13.


-- 
Ben Cotton
He / Him / His
Fedora Program Manager
Red Hat
TZ=America/Indiana/Indianapolis