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closures test: Avoid timeout on ARM64 CPUs

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Closures use a 16-bit atomic reference count, which is really slow
on certain ARM64 CPUs such as the Cortex-A57 (glib#1316). This is
non-trivial to solve, since the public struct field cannot be enlarged
to 32-bit while preserving ABI, and 16-bit atomic operations would be new
(and rather niche) API.

Until this can be solved properly (hopefully in GLib 2.59.x), cut down
the number of signal emission cycles and bump up the timeout in the
Meson build system, so that builds won't time out. We can't just take
another zero off the number of signal emission cycles, as was done in the
original version of this patch in Debian, because if we do that it can
result in test failures when the main thread starves the other threads.

ARM64 CPUs are backwards-compatible with 32-bit ARM, and the same
slowdown can be seen when building and testing 32-bit code on these
CPUs, so check for both 32- and 64-bit ARM.

Bug-Debian: https://bugs.debian.org/880883
Co-authored-by: Iain Lane <laney@debian.org>
Signed-off-by: Simon McVittie <smcv@debian.org>
This commit is contained in:
Simon McVittie 2017-12-18 10:47:29 +00:00 committed by Simon McVittie
parent b09a0df9a9
commit cb98e37357
2 changed files with 19 additions and 0 deletions
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12
tests/refcount/closures.c
View File

@ -259,7 +259,19 @@ main (int argc,
thread1 = g_thread_create (thread1_main, closure, TRUE, NULL);
thread2 = g_thread_create (thread2_main, closure, TRUE, NULL);
/* The 16-bit compare-and-swap operations currently used for closure
* refcounts are really slow on some ARM CPUs, notably Cortex-A57.
* Reduce the number of iterations so that the test completes in a
* finite time, but don't reduce it so much that the main thread
* starves the other threads and causes a test failure.
*
* https://gitlab.gnome.org/GNOME/glib/issues/1316
* aka https://bugs.debian.org/880883 */
#if defined(__aarch64__) || defined(__arm__)
for (i = 0; i < 100000; i++)
#else
for (i = 0; i < 1000000; i++)
#endif
{
static guint count = 0;
test_emissions (object);

7
tests/refcount/meson.build
View File

@ -54,6 +54,13 @@ foreach test_name, extra_args : refcount_tests
suite = ['refcount'] + extra_args.get('suite', [])
timeout = suite.contains('slow') ? test_timeout_slow : test_timeout
# https://gitlab.gnome.org/GNOME/glib/issues/1316
# aka https://bugs.debian.org/880883
if test_name == 'closures' and ['arm', 'aarch64'].contains(host_cpu_family)
timeout = timeout * 10
endif
# FIXME? TESTS_ENVIRONMENT = LIBCHARSET_ALIAS_DIR=$(top_builddir)/glib/libcharset
test(test_name, exe, env : test_env, timeout : timeout, suite : suite)
endforeach