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SubjectRe: [RFC PATCH for 4.15 v3 15/22] rseq: selftests: Provide self-tests
----- On Nov 21, 2017, at 12:40 PM, shuah shuah@kernel.org wrote:

> On 11/21/2017 10:05 AM, Mathieu Desnoyers wrote:
>> ----- On Nov 21, 2017, at 10:34 AM, shuah shuah@kernel.org wrote:
>>
>> [...]
>>>> ---
>>>> MAINTAINERS | 1 +
>>>> tools/testing/selftests/Makefile | 1 +
>>>> tools/testing/selftests/rseq/.gitignore | 4 +
>>>
>>> Thanks for the .gitignore files. It is commonly missed change, I end
>>> up adding one to clean things up after tests get in.
>>
>> I'm used to receive patches where contributors forget to add new files
>> to gitignore within my own projects, which may contribute to my awareness
>> of this pain point. :)
>>
>> [...]
>>
>>>> +
>>>> +void *test_percpu_inc_thread(void *arg)
>>>> +{
>>>> + struct inc_thread_test_data *thread_data = arg;
>>>> + struct inc_test_data *data = thread_data->data;
>>>> + long long i, reps;
>>>> +
>>>> + if (!opt_disable_rseq && thread_data->reg
>>>> + && rseq_register_current_thread())
>>>> + abort();
>>>> + reps = thread_data->reps;
>>>> + for (i = 0; i < reps; i++) {
>>>> + int cpu, ret;
>>>> +
>>>> +#ifndef SKIP_FASTPATH
>>>> + /* Try fast path. */
>>>> + cpu = rseq_cpu_start();
>>>> + ret = rseq_addv(&data->c[cpu].count, 1, cpu);
>>>> + if (likely(!ret))
>>>> + goto next;
>>>> +#endif
>>>
>>> So the test needs to compiled with this enabled? I think it would be better
>>> to make this an argument to be abel to select at test start time as opposed
>>> to making this compile time option. Remember that these tests get run in
>>> automated test rings. Making this a compile time otpion pertty much ensures
>>> that this path will not be tested.
>>>
>>> So I would reccommend adding a paratemer.
>>>
>>>> + slowpath:
>>>> + __attribute__((unused));
>>>> + for (;;) {
>>>> + /* Fallback on cpu_opv system call. */
>>>> + cpu = rseq_current_cpu();
>>>> + ret = cpu_op_addv(&data->c[cpu].count, 1, cpu);
>>>> + if (likely(!ret))
>>>> + break;
>>>> + assert(ret >= 0 || errno == EAGAIN);
>>>> + }
>>>> + next:
>>>> + __attribute__((unused));
>>>> +#ifndef BENCHMARK
>>>> + if (i != 0 && !(i % (reps / 10)))
>>>> + printf_verbose("tid %d: count %lld\n", (int) gettid(), i);
>>>> +#endif
>>>
>>> Same comment as before. Avoid compile time options.
>>
>> The goal of those compiler define are to generate the altered code without
>> adding branches into the fast-paths.
>
> That makes sense. You are looking to not add any overhead.
>
>>
>> Here is an alternative solution that should take care of your concern: I'll
>> build multiple targets for param_test.c:
>>
>> param_test
>> param_test_skip_fastpath (built with -DSKIP_FASTPATH)
>> param_test_benchmark (build with -DBENCHMARK)
>>
>> I'll update run_param_test.sh to run both param_test and
>> param_test_skip_fastpath.
>>
>> Note that "param_test_benchmark" is only useful for benchmarking,
>> so I don't plan to run it from run_param_test.sh which is meant
>> to track regressions.
>>
>> Is that approach OK with you ?
>>
>
> Yes. This approach addresses my concern about coverage for both paths.

fyi, the updated patches can be found here:

https://git.kernel.org/pub/scm/linux/kernel/git/rseq/linux-rseq.git/commit/?h=rseq/dev&id=a0b8eb0eb5d4d8a280969370aa1dcf51801139c6
"selftests: lib.mk: Introduce OVERRIDE_TARGETS"

https://git.kernel.org/pub/scm/linux/kernel/git/rseq/linux-rseq.git/commit/?h=rseq/dev&id=4ef0214e19bb7415fe7aed6852859b8d66e09a45
"cpu_opv: selftests: Implement selftests (v4)"

https://git.kernel.org/pub/scm/linux/kernel/git/rseq/linux-rseq.git/commit/?h=rseq/dev&id=7d7530b843c7ecb50bea5a136c776cf3e9155d43
"rseq: selftests: Provide self-tests (v4)"

Thanks for the feedback!

Mathieu

>
> thanks,
> -- Shuah

--
Mathieu Desnoyers
EfficiOS Inc.
http://www.efficios.com

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