Re: [igt-dev] [PATCH i-g-t v3] tests/kms_concurrent: Move bandwidth calculation to igt_fixture

["Kahola, Mika" <mika.kahola@intel.com>]

-----Original Message-----
From: Latvala, Petri <petri.latvala@intel.com> 
Sent: Tuesday, March 31, 2020 9:45 AM
To: Kahola, Mika <mika.kahola@intel.com>
Cc: igt-dev@lists.freedesktop.org; juhapekka.heikkila@gmail.com; Lisovskiy, Stanislav <stanislav.lisovskiy@intel.com>
Subject: Re: [PATCH i-g-t v3] tests/kms_concurrent: Move bandwidth calculation to igt_fixture

On Mon, Mar 30, 2020 at 02:02:29PM +0300, Mika Kahola wrote:
> The commit 153b34b5353df8c18a87d ("tests/kms_concurrent:
> Test maximum number of planes supported by the platform") caused 
> regression on HSW pipe B testing such as.
> 
> IGT-Version: 1.25-gfd8248084 (x86_64) (Linux: 
> 5.6.0-rc7-CI-CI_DRM_8194+ x86_64) Starting subtest: pipe-B Testing 
> resolution with connector VGA-1 using pipe B with seed 1585245074 
> child 0 died with signal 11, Segmentation fault Subtest pipe-B: FAIL 
> (0.330s)
> 
> To fix this, we need move bandwidth calculation routines into part of 
> igt_fixture instead of calculating it just before actual testing. The 
> patch takes the minimum of those maximum number of planes for given output.
> 
> v2: Limit bandwidth check only gen11+ (CI)
> v3: Loop child process 5x longer when running test with 1 iteration 
> (CI)
> 
> Signed-off-by: Mika Kahola <mika.kahola@intel.com>
> ---
>  tests/kms_concurrent.c | 30 ++++++++++++++++--------------
>  1 file changed, 16 insertions(+), 14 deletions(-)
> 
> diff --git a/tests/kms_concurrent.c b/tests/kms_concurrent.c index 
> 1403e990..31c5620a 100644
> --- a/tests/kms_concurrent.c
> +++ b/tests/kms_concurrent.c
> @@ -36,6 +36,7 @@ typedef struct {
>  	igt_display_t display;
>  	igt_plane_t **plane;
>  	struct igt_fb *fb;
> +	int max_planes;
>  } data_t;
>  
>  /* Command line parameters. */
> @@ -223,13 +224,13 @@ test_plane_position_with_output(data_t *data, enum pipe pipe, int max_planes,
>  				igt_output_t *output)
>  {
>  	int i;
> -	int iterations = opt.iterations < 1 ? 1 : opt.iterations;
> +	int iterations = opt.iterations < 5 ? 1 : opt.iterations;

This changes nothing though for CI. You still use 1. In fact this just limits the iterations to 1 for everyone who specifies more than 1, until they use 5 or more.

And still, this patch needs an actual explanation why the crash happened and why doing the same calculation in a fixture help. Otherwise there's no guarantee it won't happen again. Until proven otherwise, avoiding the crash is accidental.

I investigated this a bit further and I noticed that for yet unidentified reason the bandwidth calculation returned different number of planes for pipe B. This was too much to handle on actual test and therefore child exited too early.

There seems to be a simpler way of computing how many planes we can support with the given bandwidth. I propose that we disregard this patch and I will propose and test another kind of solution.

-Mika- 
--
Petri Latvala
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