Author: David Schneider <david.schnei...@picle.org>
Branch: extradoc
Changeset: r4501:909c51d589b3
Date: 2012-08-10 14:54 +0200
http://bitbucket.org/pypy/extradoc/changeset/909c51d589b3/
Log: Write about the guard failure frequency
diff --git a/talk/vmil2012/paper.tex b/talk/vmil2012/paper.tex
--- a/talk/vmil2012/paper.tex
+++ b/talk/vmil2012/paper.tex
@@ -708,12 +708,31 @@
\subsection{Guard Failures}
\label{sub:guard_failure}
+The last point in this discussion is the frequency of guard failures.
+Figure~\ref{fig:failing_guards} presents for each benchmark a list of the
+relative amounts of guards that ever fail and of guards that fail more than 200
+times. For guards that fail more than 200 times, as described before, a trace
+is recorded that starts from the guard, patching the guard so that later
+failures execute the new trace instead of taking the side-exit. Hence the
+numbers presented for guards that fail more than 200 times represent the 200
+failures up to the compilation of the bridge and all executions of the then
+attached bridge.
+
\begin{figure}
\include{figures/failing_guards_table}
\caption{Failing guards}
\label{fig:failing_guards}
\end{figure}
+From Figure~\ref{fig:failing_guards} we can see that only a very small amount
+of all the guards in the optimized traces ever fail. This amount varies between
+2.4\% and 5.7\% of all guards. As can be expected, even less guards fail often
+enough that a bride is compiled for them, only 1.2\% to 3.6\% of all guards
+fail more than 200 times. Also of all failing guards a few fail extremely often
+and most fail rarely. The results emphasizes that as most of the guards never
+fail it is important to make sure that the successful execution of a guard does
+not have unnecessary overhead.
+
\todo{add a footnote about why guards have a threshold of 200}
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