On Wednesday, 19 January 2022 04:23:22 PST Allan Sandfeld Jensen wrote: > On Mittwoch, 19. Januar 2022 04:01:06 CET Thiago Macieira wrote: > > 5) for glibc-based Linux, add v3 sub-arch by default > > > > I'd like to raise the default on Linux from baseline to v2 *and* add a v3 > > sub- arch build, as described by point #3 above. > > > > Device-specific Qt builds (Yocto Project, Boot2Qt) would need to turn this > > off and select a single architecture, if they don't want the extra files. > > I am also sceptical what we would gain from that. It seems mostly like > something that could benefit QtCore, so perhaps only do v3 sub-arch there?
That is what I'm proposing: do the extra, v3 sub-arch for only a few select libraries. Off the top of my head, that's QtCore, QtGui and some Qt 3D ones. Anything that is math-heavy would benefit > Do Clear Linux have numbers for what they have gained by using a v3 like > default? v3 is not the default, v2 is. But we do build qtbase and qt3d as v2+v3, plus quite a few more packages (and a handful are v2+v3+v4). As I mentioned in the reply to Lars, just search for benchmarks on phoronix.com. The benefit isn't a lot in the general case. It's a few percent here and there, but it's consistent. You get far more with dedicated algorithms, which is why I am optimising qstring.cpp for AVX512VL. Yesterday, while debugging QTBUG-91739, I got the opportunity to benchmark ucstrncmp (QtPrivate::compareStrings). See [1] for details, but it showed a 20% improvement on v3 over v2 and an additional 10.7% on v4 over v3 (for 28.8% gain overall). Please note that the v2 and v3 code are already using the new epilogue code I added in [2] plus all the cross- platform optimisations listed in that JIRA comment, so this is all already better than what you have. However, note that all strings had the same 90-byte (45-character) length, so this is not very representative of the real world. In particular, the AVX512VL code should show an extra improvement for strings under 16 characters and this wasn't exercised. [1] https://bugreports.qt.io/browse/QTBUG-91739? focusedCommentId=641671#comment-641671 [2] https://codereview.qt-project.org/c/qt/qtbase/+/390698 -- Thiago Macieira - thiago.macieira (AT) intel.com Software Architect - Intel DPG Cloud Engineering _______________________________________________ Development mailing list Development@qt-project.org https://lists.qt-project.org/listinfo/development
