Bug 1244: changes to description pospopcount

[libreriscv.git] / conferences / fosdem2024 / fosdem2024_ddffirst / fosdem2024_ddffirst.tex

diff --git a/conferences/fosdem2024/fosdem2024_ddffirst/fosdem2024_ddffirst.tex b/conferences/fosdem2024/fosdem2024_ddffirst/fosdem2024_ddffirst.tex
index a76f7e537f1bfc888e380c062f6d5611930e493d..58550e9924ebba6c72e407f02f245cbe5dddb5ca 100644 (file)
--- a/conferences/fosdem2024/fosdem2024_ddffirst/fosdem2024_ddffirst.tex
+++ b/conferences/fosdem2024/fosdem2024_ddffirst/fosdem2024_ddffirst.tex
@@ -2,6 +2,8 @@
 \usepackage{beamerthemesplit}
 \usepackage{graphics}
 \usepackage{pstricks}
+\usepackage{pgffor}
+\usepackage{listings}
 
 \graphicspath{{./}}
 
@@ -96,22 +98,12 @@
 
 
 
-%%\frame{\frametitle{Simple SBC-style SoC}
-%%
-%%\begin{center}
-%%\includegraphics[width=0.9\textwidth]{shakti_libre_soc.jpg}
-%%\end{center}
-
-%%}
-
-
-
-
 \begin{frame}[fragile]
 \frametitle{Simple-V CMPI in a nutshell}
 
 \begin{semiverbatim}
 function op\_cmpi(BA, RA, SI) # cmpi not vector-cmpi!
+  (assuming you know power-isa)
   int i, id=0, ira=0;
   for (i = 0; i < VL; i++)
     CR[BA+id] <= compare(ireg[RA+ira], SI);
@@ -127,37 +119,130 @@ function op\_cmpi(BA, RA, SI) # cmpi not vector-cmpi!
 \end{frame}
 
 
-\frame{\frametitle{Additional Simple-V features}
-
- \begin{itemize}
-   \item "fail-on-first" (POWER9 VSX strncpy segfaults on boundary!)
-   \item "Twin Predication" (covers VSPLAT, VGATHER, VSCATTER, VINDEX etc.)
-   \item SVP64: extensive "tag" (Vector context) augmentation
-   \item "Context propagation": a VLIW-like context.  Allows contexts
-         to be repeatedly applied.
-          Effectively a "hardware compression algorithm" for ISAs.
-   \item Ultimate goal: cut down I-Cache usage, cuts down on power
-   \item Typical GPU has its own I-Cache and small shaders.\\
-        \textit{We are a Hybrid CPU/GPU: I-Cache is not separate!}
-   \item Needs to go through OpenPOWER Foundation `approval'         
-  \end{itemize}
+\frame{\frametitle{Load/Store Fault-First}
+       
+       \begin{itemize}
+               \item Problem: vector load and store can cause a page fault
+               \item Solution: a protocol that allows optional load/store
+               \item instruction \textit{requests} a number of elements
+               \item instruction \textit{informs} the number actually loaded
+               \item first element load/store is not optional (cannot fail)
+        \item ARM SVE: https://arxiv.org/pdf/1803.06185.pdf
+        \item more: wikipedia Vector processor page: Fault/Fail First
+        \vspace{10pt}
+               \item Load/Store is Memory to/from Register, what about
+              Register to Register?
+        \item Register-to-register: "Data-Dependent Fail-First."
+        \item Z80 LDIR: Mem-Register, CPIR: Register-Register
+       \end{itemize}
 }
 
+\begin{frame}[fragile]
+       \frametitle{Data-Dependent-Fail-First in a nutshell}
+       
+       \begin{semiverbatim}
+function op\_cmpi(BA, RA, SI) # cmpi not vector-cmpi!
+int i, id=0, ira=0;
+for (i = 0; i < VL; i++)
+    CR[BA+id] <= compare(ireg[RA+ira], SI);
+    if (reg\_is\_vectorised[BA] ) \{ id += 1; \}
+    if (reg\_is\_vectorised[RA])  \{ ira += 1; \}
+    if test (CR[BA+id]) == FAIL: \{ VL = i + 1; break \}
+       \end{semiverbatim}
+       
+       \begin{itemize}
+               \item Parallelism still perfectly possible
+                     ("hold" writing results until sequential post-analysis
+                      carried out. Best done with OoO)
+               \item VL truncation can be inclusive or exclusive
+                     (include or exclude a NULL pointer or a
+                     string-end character, or overflow result)
+               \item \textit{Truncation can be to zero Vector Length}
+       \end{itemize}
+\end{frame}
+
+\frame{\frametitle{Power ISA v3.1 vstribr}
+       
+       \lstinputlisting[language={}]{vstribr.txt}
+       
+       \begin{itemize}
+               \item ironically this hard-coded instruction is
+               identical to general-purpose Simple-V DD-FFirst...
+       \end{itemize}
+       
+}Po
+
 \frame{\frametitle{maxloc}
   \begin{itemize}
                \item "TODO
   \end{itemize}
 }
+
 \frame{\frametitle{Pospopcount}
+       
   \begin{itemize}
-       \item "TODO
-  \end{itemize}        
+       \item   Positional popcount adds up the totals of each bit set to 1 in each bit-position, of an array of input values.
+       \item   Notoriously difficult to do in SIMD assembler: typically 550 lines
+
+   \end{itemize}
+       
+       \lstinputlisting[language={}]{pospopcount.c}
+       
 }
+
+\frame{\frametitle{Pospopcount}
+       
+       \begin{center}
+               \includegraphics[width=0.6\textwidth]{pospopcount.png}
+       \end{center}
+         \begin{itemize}
+               \item   The challenge is to perform an appropriate transpose of the data (the CPU can only work on registers, horizontally),
+               in blocks that suit the processor and the ISA capacity.
+
+               
+       \end{itemize}
+}
+
+\frame{\frametitle{Pospopcount}
+       
+       \begin{center}
+               \includegraphics[width=0.6\textwidth]{array_popcnt.png}
+       \end{center}
+
+  \begin{itemize}
+
+               \item   The draft gbbd instruction implements the transpose (shown above), 
+                               preparing the data to use the standard popcount instruction.
+
+       
+       \end{itemize}
+       
+}
+
+\frame{\frametitle{Pospopcount.s}
+
+
+\lstinputlisting[language={}]{pospopcount.s}
+
+}
+
+
 \frame{\frametitle{strncpy}
+
+       \lstinputlisting[language={}]{strncpy.c}
   \begin{itemize}
        \item "TODO
  \end{itemize} 
 }
+
+
+
+\frame{\frametitle{strncpy assembler}
+
+\lstinputlisting[language={}]{strncpy.s}
+
+}
+
 \frame{\frametitle{linked-list walking}        
   \begin{itemize}
        \item "TODO