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From: "cvs-commit at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org> To: gcc-bugs@gcc.gnu.org Subject: [Bug libstdc++/68606] Reduce or disable the static emergency pool for C++ exceptions Date: Tue, 11 Oct 2022 15:22:52 +0000 [thread overview] Message-ID: <bug-68606-4-jDGeWTTe6k@http.gcc.gnu.org/bugzilla/> (raw) In-Reply-To: <bug-68606-4@http.gcc.gnu.org/bugzilla/> https://gcc.gnu.org/bugzilla/show_bug.cgi?id=68606 --- Comment #21 from CVS Commits <cvs-commit at gcc dot gnu.org> --- The master branch has been updated by Jonathan Wakely <redi@gcc.gnu.org>: https://gcc.gnu.org/g:637e3668fdc17c4e226538fb14f9fab225433d01 commit r13-3234-g637e3668fdc17c4e226538fb14f9fab225433d01 Author: Jonathan Wakely <jwakely@redhat.com> Date: Wed Oct 5 21:21:54 2022 +0100 libstdc++: Allow emergency EH alloc pool size to be tuned [PR68606] Implement a long-standing request to support tuning the size of the emergency buffer for allocating exceptions after malloc fails, or to disable that buffer entirely. It's now possible to disable the dynamic allocation of the buffer and use a fixed-size static buffer, via --enable-libstdcxx-static-eh-pool. This is a built-time choice that is baked into libstdc++ and so affects all code linked against that build of libstdc++. The size of the pool can be set by --with-libstdcxx-eh-pool-obj-count=N which is measured in units of sizeof(void*) not bytes. A given exception type such as std::system_error depends on the target, so giving a size in bytes wouldn't be portable across 16/32/64-bit targets. When libstdc++ is configured to use a dynamic buffer, the size of that buffer can now be tuned at runtime by setting the GLIBCXX_TUNABLES environment variable (c.f. PR libstdc++/88264). The number of exceptions to reserve space for is controlled by the "glibcxx.eh_pool.obj_count" and "glibcxx.eh_pool.obj_size" tunables. The pool will be sized to be able to allocate obj_count exceptions of size obj_size*sizeof(void*) and obj_count "dependent" exceptions rethrown by std::rethrow_exception. With the ability to tune the buffer size, we can reduce the default pool size on 32-bit and 16-bit targets. Most users never need to throw 1kB exceptions in parallel from hundreds of threads after malloc is OOM. The users who do need that can use the tunables to select larger sizes. The old defaults can be chosen at runtime by setting GLIBCXX_TUNABLES to: 64-bit: glibcxx.eh_pool.obj_count=64:glibcxx.eh_pool.obj_size=112 32-bit: glibcxx.eh_pool.obj_count=32:glibcxx.eh_pool.obj_size=104 Or approximated by configuring with: 64-bit: --with-libstdcxx-eh-pool-obj-count=252 32-bit: --with-libstdcxx-eh-pool-obj-count=94 libstdc++-v3/ChangeLog: PR libstdc++/68606 * Makefile.in: Regenerate. * acinclude.m4 (GLIBCXX_EMERGENCY_EH_ALLOC): New macro. * configure: Regenerate. * configure.ac: Use GLIBCXX_EMERGENCY_EH_ALLOC. * crossconfig.m4: Check for secure_getenv. * doc/Makefile.in: Regenerate. * doc/xml/manual/configure.xml: Document new configure options. * doc/xml/manual/evolution.xml: Document addition of tunables. * doc/xml/manual/using_exceptions.xml: Document emergency buffer and tunables. * doc/html/*: Regenerate. * include/Makefile.in: Regenerate. * libsupc++/Makefile.am: Use EH_POOL_FLAGS. * libsupc++/Makefile.in: Regenerate. * libsupc++/eh_alloc.cc (EMERGENCY_OBJ_SIZE): Define in units of sizeof(void*) not including the ABI's exception header. (EMERGENCY_OBJ_COUNT): Define as target-independent calculation based on word size. (MAX_OBJ_COUNT): Define macro for upper limit on pool size. (pool) [_GLIBCXX_EH_POOL_STATIC]: Use fixed-size buffer. (pool::buffer_size_in_bytes): New static member function. (pool::pool): Parse GLIBCXX_TUNABLES environment variable to set pool size at runtime. (pool::in_pool): Use std::less<void*> for total order. (__freeres) [_GLIBCXX_EH_POOL_STATIC]: Do nothing. (__cxa_free_exception, __cxa_free_dependent_exception): Add [[unlikely]] attributes. * po/Makefile.in: Regenerate. * python/Makefile.in: Regenerate. * src/Makefile.in: Regenerate. * src/c++11/Makefile.in: Regenerate. * src/c++17/Makefile.in: Regenerate. * src/c++20/Makefile.in: Regenerate. * src/c++98/Makefile.in: Regenerate. * src/filesystem/Makefile.in: Regenerate. * src/libbacktrace/Makefile.in: Regenerate. * testsuite/Makefile.in: Regenerate.
next prev parent reply other threads:[~2022-10-11 15:23 UTC|newest] Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top [not found] <bug-68606-4@http.gcc.gnu.org/bugzilla/> 2020-05-23 15:45 ` egallager at gcc dot gnu.org 2022-09-28 7:00 ` dumoulin.thibaut at gmail dot com 2022-09-28 14:01 ` rdiezmail-gcc at yahoo dot de 2022-09-28 14:42 ` dumoulin.thibaut at gmail dot com 2022-09-28 15:14 ` rdiezmail-gcc at yahoo dot de 2022-09-28 20:20 ` redi at gcc dot gnu.org 2022-09-28 20:24 ` redi at gcc dot gnu.org 2022-09-29 7:02 ` rguenth at gcc dot gnu.org 2022-09-29 9:31 ` redi at gcc dot gnu.org 2022-09-29 12:24 ` dumoulin.thibaut at gmail dot com 2022-09-29 13:01 ` redi at gcc dot gnu.org 2022-10-07 15:55 ` redi at gcc dot gnu.org 2022-10-11 15:22 ` cvs-commit at gcc dot gnu.org [this message] 2022-10-11 15:25 ` redi at gcc dot gnu.org
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