On Mon, Jul 22, 2019 at 3:27 PM Ben Cotton <bcot...@redhat.com> wrote: > > https://fedoraproject.org/wiki/Changes/x86-64_micro-architecture_update > > == Summary == > Fedora currently uses the original K8 micro-architecture (without > 3DNow! and other AMD-specific parts) as the baseline for its > <code>x86_64</code> architecture. This baseline dates back to 2003 > and has not been updated since. As a result, performance of Fedora is > not as good as it could be on current CPUs. > > This change to update the micro-architecture level for the > architecture to something more recent. > > == Owner == > * Name: [[User:fweimer| Florian Weimer]] > * Email: [mailto:fwei...@redhat.com fwei...@redhat.com] > > == Detailed Description == > > After preliminary discussions with CPU vendors, we propose AVX2 as the > new baseline. AVX2 support was introduced into CPUs from 2013 to > 2015. See > [https://en.wikipedia.org/wiki/Advanced_Vector_Extensions#CPUs_with_AVX2 > CPUs with AVX2].
Would it be possible to include some basic instructions or a script for people to run on their systems to see if they are AVX2 compliant? That would help them assess the impact. josh > Along with AVX2, it makes sense to enable certain other CPU features > which are not strictly implied by AVX2, such as CMPXCHG16B, FMA, and > earlier vector extensions such as SSE 4.2. Details are still being > worked out. > > A test rebuild of a distribution largely based on Fedora 28 showed > that there is only a small number of build failures due to the > baseline switch. Very few packages are confused about the availability > of the CMPXCHG16B instruction, leading to linking failures related to > <code>-latomic</code>, and there are some hard-coded floating point > results that could change due to vectorization. (The latter is within > bounds of the usual cross-architecture variation for such tests.) > > == Benefit to Fedora == > > Fedora will use current CPUs more efficiently, increasing performance > and reducing power consumption. > > Moreover, when Fedora is advertised as a distribution by a compute > service provider, users can be certain that their AVX2-optimized > software will run in this environment. > > == Scope == > * Proposal owners: Update the <code>gcc</code> and > <code>redhat-rpm-config</code> package to implement the new compiler > flags. It is expected that the new baseline will be implemented in a > new GCC <code>-march=</code> option for convenience. > > * Other developers: Other developers may have to adjust test suites > which expect exact floating point results, and correct linking with > <code>libatomic</code>. They will also have to upgrade their x86-64 > machines to something that can execute AVX2 instructions. > > * Release engineering: [https://pagure.io/releng/issue/8513 #8513] > ** All Fedora builders need to be AVX2-capable. > ** Infrastructure ticket: > [https://pagure.io/fedora-infrastructure/issue/7968 #7968] > * Policies and guidelines: No guidelines need to be changed. > * Trademark approval: N/A (not needed for this Change) > > == Upgrade/compatibility impact == > Fedora installations on systems with CPUs which are not able to > execute AVX2 instructions will not be able to upgrade. > > == How To Test == > General system testing will provide test coverage for this change. > > == User Experience == > User should observe improved performance and, likely, battery life. > Developers will benefit from the knowledge that code with AVX2 > optimizations will run wherever Fedora runs. > > == Dependencies == > There are no direct dependencies on this change at this time. > > == Contingency Plan == > It is possible to not implement this change, or implement a smaller > subset of it (adopting the CMPXCHG16B instruction only, for example). > > * Contingency mechanism: Mass rebuild with different/previous compiler glags. > * Contingency deadline: Final mass rebuild. > * Blocks release? No. > * Blocks product? No. > > == Documentation == > The new micro-architecture baseline and the resulting requirements > need to be documented. > > == Release Notes == > Release notes must mention how users can determine whether their > system supports AVX2 prior to upgrading, for example by running > <code>grep avx2 /proc/cpuinfo</code>. > > -- > Ben Cotton > He / Him / His > Fedora Program Manager > Red Hat > TZ=America/Indiana/Indianapolis > _______________________________________________ > devel mailing list -- devel@lists.fedoraproject.org > To unsubscribe send an email to devel-le...@lists.fedoraproject.org > Fedora Code of Conduct: > https://docs.fedoraproject.org/en-US/project/code-of-conduct/ > List Guidelines: https://fedoraproject.org/wiki/Mailing_list_guidelines > List Archives: > https://lists.fedoraproject.org/archives/list/devel@lists.fedoraproject.org _______________________________________________ devel mailing list -- devel@lists.fedoraproject.org To unsubscribe send an email to devel-le...@lists.fedoraproject.org Fedora Code of Conduct: https://docs.fedoraproject.org/en-US/project/code-of-conduct/ List Guidelines: https://fedoraproject.org/wiki/Mailing_list_guidelines List Archives: https://lists.fedoraproject.org/archives/list/devel@lists.fedoraproject.org
