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.nik...@intel.com>
Cc: Daniel Vetter <daniel.vet...@intel.com>
Signed-off-by: Gabriel Feceoru <gabriel.fece...@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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