[PATCH] x86: Add --enable-rdtscp-in-benchtests

[Szabolcs Nagy]

On 23/10/18 11:58, H.J. Lu wrote:
> On 10/23/18, Siddhesh Poyarekar <siddhesh@gotplt.org> wrote:
>> On 23/10/18 2:34 PM, Florian Weimer wrote:
>>> Shouldn't the benchtests use clock_gettime anyway, to avoid issues in
>>> case the TSC is not synchronized across cores?
>>
>> There's an option USE_CLOCK_GETTIME to make benchtests do that, but
>> otherwise it uses the hp_timing bits by default.
> 
> I want something better that rdtsc and very low overhead since some bench
> tests only last a few cycles.  Adding lfence may make timing data look like
> noise.
> 

ideally bench test should be fixed so clock_gettime gives
stable enough results.

target specific timers are not always available and their
results are hard to interpret compared to a standard api
that returns wall clock time in sane units.