Re: [RFC i-g-t v3] tests/gem_exec_pad_to_size: Test object padding at execbuf

[Tvrtko Ursulin <tvrtko.ursulin@linux.intel.com>]

On 04/01/2015 04:42 PM, Chris Wilson wrote:
> On Wed, Apr 01, 2015 at 04:14:52PM +0100, Tvrtko Ursulin wrote:
>> +	/* Re-exec with padding set. */
>> +	igt_assert(exec(fd, eb_handles, pad_to_size, offsets) == 0);
>
> The crux of the test is that we generate two objects such that
>
> B_offset = A_offset + A_size
>
> and then tell the kernel that A is actually 2*size (A_pad_to_size)
>
>> +	if (offsets[1] > offsets[0])
>> +		distance = offsets[1] - offsets[0];
>> +	else
>> +		distance = offsets[0] - offsets[1];
>
> The assertion I feel should only be that
>
> B_offset + B_size <= A_offset && B_offset >= A_offset + A_pad_to_size

I don't get this. B starts after A + padding, but B ends before A?

> i.e. that they are now disjoint.
>
> Your test is valid nevertheless, it is the ordering of the objects that
> is confusing.
>
> Hmm, can you loop until B_offset == A_offset + A_size such that we don't
> have the confusion with order? And even assert that A_offset is
> unchanged (though that smells like a little to much internal knowledge
> leaking through, it is a desirable property of the allocator though - no
> unnecessarily eviction) afterwards.
>
> Do you agree that losing the handling of negative distances will make
> the test simpler to understand (at the expense of doing more work in the
> setup)?

I thought my test logic is pretty straightforward:

1. Find two objects next to each other.
2. Add padding on the "lower" (addressed) object.
3. Ensure objects are now apart at least what the padding is.

Regards,

Tvrtko
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