testlib: Extend existing *_opts in extra_*_opts

Previously we'd override the existing {run,hc} opts in
extra_{run,hc}_opts, which caused flakiness in T1969, see #17712.

extra_{run,hc}_opts now extends {run,hc} opts, instead of overriding.

Also we shrank the allocation area for T1969 in order to increase
residency sampling frequency.

Fixes #17712

2 files changed, 10 insertions, 7 deletions

diff --git a/testsuite/driver/testlib.py b/testsuite/driver/testlib.py
index a4960e83bd..965350f56b 100644
--- a/testsuite/driver/testlib.py
+++ b/testsuite/driver/testlib.py
@@ -393,7 +393,7 @@ def extra_run_opts( val ):
     return lambda name, opts, v=val: _extra_run_opts(name, opts, v);
 
 def _extra_run_opts( name, opts, v ):
-    opts.extra_run_opts = v
+    opts.extra_run_opts += " " + v
 
 # -----
 
@@ -401,7 +401,7 @@ def extra_hc_opts( val ):
     return lambda name, opts, v=val: _extra_hc_opts(name, opts, v);
 
 def _extra_hc_opts( name, opts, v ):
-    opts.extra_hc_opts = v
+    opts.extra_hc_opts += " " + v
 
 # -----
 
@@ -567,13 +567,15 @@ def llvm_build ( ) -> bool:
 # appears to change (up or down) when the underlying profile hasn't
 # really changed. To further minimize this effect we run with a single
 # generation (meaning we get a residency sample on every GC) with a small
-# allocation area (as suggested in #17387).
+# allocation area (as suggested in #17387). That's what +RTS -h -i0 will do.
+# If you find that a test is flaky, sampling frequency can be adjusted by
+# shrinking the allocation area (+RTS -A64k, for example).
 #
 # However, please don't just ignore changes in residency.  If you see
 # a change in one of these figures, please check whether it is real or
 # not as follows:
 #
-#  * Run the test with old and new compilers, adding +RTS -h -i0.01
+#  * Run the test with old and new compilers, adding +RTS -h -i0.001
 #    (you don't need to compile anything for profiling or enable profiling
 #    libraries to get a heap profile).
 #  * view the heap profiles, read off the maximum residency.  If it has
diff --git a/testsuite/tests/perf/compiler/all.T b/testsuite/tests/perf/compiler/all.T
index b4910c570a..f9cedaff55 100644
--- a/testsuite/tests/perf/compiler/all.T
+++ b/testsuite/tests/perf/compiler/all.T
@@ -9,9 +9,10 @@ setTestOpts(no_lint)
 
 test('T1969',
      [# expect_broken(12437),
-      # we collect residency for reference only, hence the large acceptance window.
-      # We have seen >20% variations in this number.
-      collect_compiler_residency(50),
+      collect_compiler_residency(20),
+      extra_run_opts('+RTS -A64k -RTS'),
+          # The default RESIDENCY_OPTS is 256k and we need higher sampling
+          # frequency. Incurs a slow-down by about 2.
       collect_compiler_stats('bytes allocated', 1),
       only_ways(['normal']),