From 4c2f44f82ed44c1b9d1e2dbc3615c99277e4e4e1 Mon Sep 17 00:00:00 2001 From: lkcl Date: Thu, 20 Apr 2023 16:16:51 +0100 Subject: [PATCH] --- openpower/sv/normal.mdwn | 14 ++++++++++++-- 1 file changed, 12 insertions(+), 2 deletions(-) diff --git a/openpower/sv/normal.mdwn b/openpower/sv/normal.mdwn index f74154f3f..e913b1253 100644 --- a/openpower/sv/normal.mdwn +++ b/openpower/sv/normal.mdwn @@ -34,11 +34,12 @@ the following Modes apply to Arithmetic and Logical SVP64 operations: is performed. See [[svp64/appendix]]. Note that there are comprehensive caveats when using this mode, and it should not be confused with the Parallel Reduction [[sv/remap]]. + Also care is needed with `hphint`. Note that ffirst and reduce modes are not anticipated to be high-performance in some implementations. ffirst due to interactions -with VL, and reduce due to it requiring additional operations to produce -a result. simple and saturate are however inter-element +with VL, and reduce due to it creating overlapping operations in +many of its uses. simple and saturate are however inter-element independent and may easily be parallelised to give high performance, regardless of the value of VL. @@ -146,6 +147,15 @@ be parallelised. Dependency chain as long as Sequential Program Execution Order is preserved. Easy examples include Reduction on Logical OR or AND operations.* +**Horizontal Parallelism Hint** + +`SVSTATE.hphint` declares to hardware that groups of elements up to this +size are 100% independent. With Reduction literally creating Dependency +Hazards on every element-level sub-instruction it is pretty clear that setting +`hphint` *at all* would cause data corruption. However `sv.add *r0, *r4, *r0` +for example clearly leaves room for four parallel elements. Programmers must +be aware of this and exercise caution. + ## Data-dependent Fail-on-first Data-dependent fail-on-first is CR-field-driven and is completely separate -- 2.30.2