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gmon: Revert addition of tunables to the manual

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These tunables had to be removed over GLIBC_PRIVATE ABI stability
concerns.
This commit is contained in:
Florian Weimer 2023-04-28 17:55:39 +02:00
parent a908c18d47
commit 7c32cb7dd8
1 changed files with 0 additions and 59 deletions
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manual/tunables.texi
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@ -77,9 +77,6 @@ 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
@ -615,59 +612,3 @@ 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