From: Luke Kenneth Casson Leighton <lkcl@lkcl.net>
Date: Mon, 8 Jan 2024 11:41:09 +0000 (+0000)
Subject: bug 1244: add slide for describing load/store fault-first
X-Git-Url: https://git.libre-soc.org/?a=commitdiff_plain;h=6dbce04d6a586e250eb0fe0edf731bb5c0ad5ccd;p=libreriscv.git

bug 1244: add slide for describing load/store fault-first
---

diff --git a/conferences/fosdem2024/fosdem2024_ddffirst/fosdem2024_ddffirst.tex b/conferences/fosdem2024/fosdem2024_ddffirst/fosdem2024_ddffirst.tex
index a76f7e537..f41b20c4c 100644
--- a/conferences/fosdem2024/fosdem2024_ddffirst/fosdem2024_ddffirst.tex
+++ b/conferences/fosdem2024/fosdem2024_ddffirst/fosdem2024_ddffirst.tex
@@ -126,6 +126,36 @@ function op\_cmpi(BA, RA, SI) # cmpi not vector-cmpi!
   \end{itemize}
 \end{frame}
 
+\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 load/store is not optional     
+	\end{itemize}
+}
+
+\begin{frame}[fragile]
+	\frametitle{Data-Dependent Fail-First}
+	
+	\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; \}
+	\end{semiverbatim}
+	
+	\begin{itemize}
+		\item Above is oversimplified: predication etc. left out
+		\item Scalar-scalar and scalar-vector and vector-vector now all in one
+		\item OoO may choose to push CMPIs into instr. queue (v. busy!)
+	\end{itemize}
+\end{frame}
+
 
 \frame{\frametitle{Additional Simple-V features}