Messages in this thread Patch in this message | | | Date | Fri, 24 Nov 2023 20:57:52 +0100 (CET) | From | Michael Petlan <> | Subject | Re: [PATCH] perf test: Remove atomics from test_loop to avoid test failures |
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On Thu, 2 Nov 2023, Nick Forrington wrote: > The current use of atomics can lead to test failures, as tests (such as > tests/shell/record.sh) search for samples with "test_loop" as the > top-most stack frame, but find frames related to the atomic operation > (e.g. __aarch64_ldadd4_relax). > > This change simply removes the "count" variable, as it is not necessary.
Hello.
I believe that it was there to prevent the compiler to optimize the loop out or some reason like that. Hopefully, it will work even without that on all architectures with all compilers that are used for building perf...
I also think that the tests should be designed in a more robust way, so that they aren't directly dependent on exact stack frames, e.g. let's look at the "inet_pton" testcase...
The inet_pton test result check algorithm is designed to rely on exact stacktrace, without a possibility to specify something like "we want this and that in the stack trace, but otherwise, it does not matter which wrappers are aroung". Then there must be the following code to adjust the expected output exactly per architecture:
echo "ping[][0-9 \.:]+$event_name: \([[:xdigit:]]+\)" > $expected echo ".*inet_pton\+0x[[:xdigit:]]+[[:space:]]\($libc|inlined\)$" >> $expected case "$(uname -m)" in s390x) eventattr='call-graph=dwarf,max-stack=4' echo "(__GI_)?getaddrinfo\+0x[[:xdigit:]]+[[:space:]]\($libc|inlined\)$" >> $expected echo "main\+0x[[:xdigit:]]+[[:space:]]\(.*/bin/ping.*\)$" >> $expected ;; ppc64|ppc64le) eventattr='max-stack=4' echo "gaih_inet.*\+0x[[:xdigit:]]+[[:space:]]\($libc\)$" >> $expected echo "getaddrinfo\+0x[[:xdigit:]]+[[:space:]]\($libc\)$" >> $expected echo ".*(\+0x[[:xdigit:]]+|\[unknown\])[[:space:]]\(.*/bin/ping.*\)$" >> $expected ;; *) eventattr='max-stack=3' echo ".*(\+0x[[:xdigit:]]+|\[unknown\])[[:space:]]\(.*/bin/ping.*\)$" >> $expected ;; esac
Of course, since it relies on libc version, then we need patches, such as 1f85d016768f ("perf test record+probe_libc_inet_pton: Fix call chain match on x86_64") 311693ce81c9 ("perf test record+probe_libc_inet_pton: Fix call chain match on s390") fb710ddee75f ("perf test record_probe_libc_inet_pton: Fix test on s/390 where 'text_to_binary_address' now appears on the backtrace") ... which break the test when used with older libc...
I think that a better design of such test is either probing some program of ourselves that has predictable and stable function call sequence or be more robust in checking the stack trace.
Thoughts?
Michael
> > Fixes: 1962ab6f6e0b ("perf test workload thloop: Make count increments atomic") > Signed-off-by: Nick Forrington <nick.forrington@arm.com> > --- > tools/perf/tests/workloads/thloop.c | 4 +--- > 1 file changed, 1 insertion(+), 3 deletions(-) > > diff --git a/tools/perf/tests/workloads/thloop.c b/tools/perf/tests/workloads/thloop.c > index af05269c2eb8..457b29f91c3e 100644 > --- a/tools/perf/tests/workloads/thloop.c > +++ b/tools/perf/tests/workloads/thloop.c > @@ -7,7 +7,6 @@ > #include "../tests.h" > > static volatile sig_atomic_t done; > -static volatile unsigned count; > > /* We want to check this symbol in perf report */ > noinline void test_loop(void); > @@ -19,8 +18,7 @@ static void sighandler(int sig __maybe_unused) > > noinline void test_loop(void) > { > - while (!done) > - __atomic_fetch_add(&count, 1, __ATOMIC_RELAXED); > + while (!done); > } > > static void *thfunc(void *arg) > -- > 2.42.0 > > >
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