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core: introduce BR2_ENABLE_RUNTIME_DEBUG

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Some packages have optional runtime assertions, extra traces, or other
elements that can help in debugging problems. However, such runtime elements
can negatively influence performance.

In a test program performing 100K gRPC calls from a client to a local server
and receiving the returned response, we see following execution time:

    - runtime debug enabled: 1065 seconds
    - runtime debug disabled:  48 seconds

This is more than a factor 20 (!) difference. Analysis shows that the
problem mostly stems from libabseil-cpp (a dependency of gRPC) which enables
mutex deadlock analysis when the preprocessor flag 'NDEBUG' is not set,
which adds a 'backtrace()' call on every lock/unlock.  Potentially worse,
when libunwind is enabled and linked with the test program, 'backtrace()' is
not provided by glibc but by libunwind itself.

For production systems, users expect good performance out-of-the-box. In the
example above, the difference is huge and unless explicitly tested and
analyzed, users may not realize that the performance could be much better.

Address this problem by introducing a new option BR2_ENABLE_RUNTIME_DEBUG,
which can be used by packages or package infrastructures to set the
necessary flags.

Note that BR2_ENABLE_RUNTIME_DEBUG is orthogonal to BR2_ENABLE_DEBUG: the
former changes runtime behavior, while the latter is only expected to add
debug symbols to the build. Today, the cmake build system does introduce a
runtime impact when BR2_ENABLE_DEBUG is set, but that will be rectified in a
subsequent commit.

Signed-off-by: Thomas De Schampheleire <thomas.de_schampheleire@nokia.com>
Acked-by: Arnout Vandecappelle (Essensium/Mind) <arnout@mind.be>
Reviewed-by: Yann E. MORIN <yann.morin.1998@free.fr>
Signed-off-by: Yann E. MORIN <yann.morin.1998@free.fr>
This commit is contained in:
Thomas De Schampheleire 2021-06-01 16:34:06 +02:00 committed by Yann E. MORIN
parent c2a1f906d6
commit b7939fe2a0
1 changed files with 13 additions and 0 deletions
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13
Config.in
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@ -412,6 +412,19 @@ config BR2_DEBUG_3
endchoice
endif
config BR2_ENABLE_RUNTIME_DEBUG
bool "build packages with runtime debugging info"
help
Some packages may have runtime assertions, extra traces, and
similar runtime elements that can help debugging. However,
these elements may negatively influence performance so should
normally not be enabled on production systems.
Enable this option to enable such runtime debugging.
Note: disabling this option is not a guarantee that all
packages effectively removed these runtime debugging elements.
config BR2_STRIP_strip
bool "strip target binaries"
default y