Re: [PATCH v2] Add malloc micro benchmark

[Adhemerval Zanella <adhemerval.zanella@linaro.org>]

On 05/01/2018 14:17, Carlos O'Donell wrote:
> On 01/05/2018 07:50 AM, Adhemerval Zanella wrote:
>>
>>
>> On 05/01/2018 12:32, Carlos O'Donell wrote:
>>> On 01/04/2018 05:48 AM, Wilco Dijkstra wrote:
>>>> Carlos O'Donell wrote:
>>>>>
>>>>> Don't use mallopt, please make it a tunable then.
>>>>>
>>>>> The mallopt API already had 2 secret arena options which eventually became
>>>>> so well used they were baked into the API and had to be made public.
>>>>
>>>> Unfortunately tunables are not exported so you can't use them outside of GLIBC:
>>>>
>>>> /build/glibc/benchtests/bench-malloc-simple.o: In function `bench':
>>>> bench-malloc-simple.c:(.text+0x19c): undefined reference to `__tunable_set_val'
>>>> collect2: error: ld returned 1 exit status
>>>
>>> Correct, we only have a env-var frontend right now, and the internal API is not
>>> made accessible via GLIBC_PRIVATE.
>>>
>>> You have 3 options for tests:
>>>
>>> * Use the env vars to adjust test behaviour. Run the tests multiple times.
>>> * Add a new C API frontend, very valuable, but more time consuming.
>>> * Expose the existing internal C API via GLIBC_PRIVATE for testing, and throw
>>>   it away later when we get a proper C API frontend.
>>>
>>
>> Do we want a C API to tied the malloc implementation to some tunables? My
>> understanding is the tunable api idea is not really enforce retro-compability
>> (where a C api would enforce it).
>  
> If we add a C API to the tunables, we would honour that API for tunables for
> all time, but the tunables themselves would not be stable.
> 
> e.g.
> 
> * get list of tunables supported
> * get the default value for a tunable
> * get the value of a tunable
> * set the value of a tunable
> 
> So you would use this API in the tests to get the tunable list, assert the
> tcache tunable was accepted (or fail the test), and then set it to a special
> value for the part of the test that needs it.

Right, this seems a reasonable approach (although I think out of the scope for
this change).