On 11/21/2017 02:22 PM, Mathieu Desnoyers wrote:
> ----- On Nov 21, 2017, at 12:40 PM, shuah shuah@xxxxxxxxxx wrote:
>
>> On 11/21/2017 10:05 AM, Mathieu Desnoyers wrote:
>>> ----- On Nov 21, 2017, at 10:34 AM, shuah shuah@xxxxxxxxxx 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!
>
Are you going to send these to the mailing list? That way I can do a final
review and give my Ack if they look good.
thanks,
-- Shuah
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