1 files changed, 59 insertions, 0 deletions
diff --git a/manual/tunables.texi b/manual/tunables.texi
index 83cdcdac6d..8bb2f29ea5 100644
--- a/manual/tunables.texi
+++ b/manual/tunables.texi
@@ -77,6 +77,9 @@ glibc.malloc.check: 0 (min: 0, max: 3)
 				  capabilities seen by @theglibc{}
 * Memory Related Tunables::  Tunables that control the use of memory by
 			     @theglibc{}.
+* gmon Tunables::  Tunables that control the gmon profiler, used in
+                   conjunction with gprof
+
 @end menu
 
 @node Tunable names
@@ -612,3 +615,59 @@ support in the kernel if this tunable has any non-zero value.
 
 The default value is @samp{0}, which disables all memory tagging.
 @end deftp
+
+@node gmon Tunables
+@section gmon Tunables
+@cindex gmon tunables
+
+@deftp {Tunable namespace} glibc.gmon
+This tunable namespace affects the behaviour of the gmon profiler.
+gmon is a component of @theglibc{} which is normally used in
+conjunction with gprof.
+
+When GCC compiles a program with the @code{-pg} option, it instruments
+the program with calls to the @code{mcount} function, to record the
+program's call graph. At program startup, a memory buffer is allocated
+to store this call graph; the size of the buffer is calculated using a
+heuristic based on code size. If during execution, the buffer is found
+to be too small, profiling will be aborted and no @file{gmon.out} file
+will be produced. In that case, you will see the following message
+printed to standard error:
+
+@example
+mcount: call graph buffer size limit exceeded, gmon.out will not be generated
+@end example
+
+Most of the symbols discussed in this section are defined in the header
+@code{sys/gmon.h}. However, some symbols (for example @code{mcount})
+are not defined in any header file, since they are only intended to be
+called from code generated by the compiler.
+@end deftp
+
+@deftp Tunable glibc.mem.minarcs
+The heuristic for sizing the call graph buffer is known to be
+insufficient for small programs; hence, the calculated value is clamped
+to be at least a minimum size. The default minimum (in units of
+call graph entries, @code{struct tostruct}), is given by the macro
+@code{MINARCS}. If you have some program with an unusually complex
+call graph, for which the heuristic fails to allocate enough space,
+you can use this tunable to increase the minimum to a larger value.
+@end deftp
+
+@deftp Tunable glibc.mem.maxarcs
+To prevent excessive memory consumption when profiling very large
+programs, the call graph buffer is allowed to have a maximum of
+@code{MAXARCS} entries. For some very large programs, the default
+value of @code{MAXARCS} defined in @file{sys/gmon.h} is too small; in
+that case, you can use this tunable to increase it.
+
+Note the value of the @code{maxarcs} tunable must be greater or equal
+to that of the @code{minarcs} tunable; if this constraint is violated,
+a warning will printed to standard error at program startup, and
+the @code{minarcs} value will be used as the maximum as well.
+
+Setting either tunable too high may result in a call graph buffer
+whose size exceeds the available memory; in that case, an out of memory
+error will be printed at program startup, the profiler will be
+disabled, and no @file{gmon.out} file will be generated.
+@end deftp