Re: [PATCH i-g-t v3] tests/kms_flip: Adjust tolerance when counting frames

[Gabriel Feceoru <gabriel.feceoru@intel.com>]

On 13.05.2016 15:00, Chris Wilson wrote:
> On Fri, May 13, 2016 at 02:45:09PM +0300, Gabriel Feceoru wrote:
>> basic-flip-vs-wf_vblank subtest sometimes fails asserting counted frames to
>> be aproximately equal with the estimated number.
>>
>> This is a false negative, one of the reasons being the precision lost when
>> truncating a fractional number.
>>
>> Fixed this by using floating point arithmetic.
>>
>> Cc: Jani Nikula <jani.nikula@intel.com>
>> Cc: Daniel Vetter <daniel.vetter@intel.com>
>> Signed-off-by: Gabriel Feceoru <gabriel.feceoru@intel.com>
>> ---
>>   tests/kms_flip.c | 8 ++++----
>>   1 file changed, 4 insertions(+), 4 deletions(-)
>>
>> diff --git a/tests/kms_flip.c b/tests/kms_flip.c
>> index eda2fcc..6ec97d0 100644
>> --- a/tests/kms_flip.c
>> +++ b/tests/kms_flip.c
>> @@ -1182,13 +1182,13 @@ static void check_final_state(struct test_output *o, struct event_state *es,
>>   	/* Verify we drop no frames, but only if it's not a TV encoder, since
>>   	 * those use some funny fake timings behind userspace's back. */
>>   	if (o->flags & TEST_CHECK_TS && !analog_tv_connector(o)) {
>> -		int expected;
>> +		double expected;
>>   		int count = es->count;
>>
>>   		count *= o->seq_step;
>> -		expected = elapsed / frame_time(o);
>
> int expected = count * frame_time(o);
> igt_assert_f(100 * expected >= elasped * 99 && 100 * count <= expected * 101,
> 	     "dropped frames, expected %d, counted %d, encoder type %d\n",
> 	     elapsed / frame_time(o), count, o->kencoder[0]->encoder_type);
>
> if I understood your concern correctly, as the only loss of precison
> there would be from calculating 'expected'.

That would also do it, but with care where to use the cast:

int expected =  (int)((double)count * frame_time(o));
vs
int expected = count * (int)frame_time(o);

Gabriel.

> -Chris
>
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