Re: [PATCH] drm/i915: Add module param to test the load detect code

Chris Wilson
2015-03-03T21:15:30Z

On Tue, Mar 03, 2015 at 11:23:53AM -0800, Jesse Barnes wrote:
> On 03/03/2015 09:03 AM, Daniel Vetter wrote:
> > This is useful for writing igts to make sure we don't break this,
> > without being forced to own a one of these dinosaurs.
> >
> > Suggested-by: Jesse Barnes <jbarnes@virtuousgeek.org>
> > Cc: Matt Roper <matthew.d.roper@intel.com>
> > Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
> > ---
> > drivers/gpu/drm/i915/i915_drv.h | 1 +
> > drivers/gpu/drm/i915/i915_params.c | 8 +++++++-
> > drivers/gpu/drm/i915/intel_crt.c | 6 ++++--
> > 3 files changed, 12 insertions(+), 3 deletions(-)
>
> See below for comments.
>
> I think there's probably even more room for testing like this. E.g. the
> tiled swapping test could be done this way rather than trying to force
> swapping. Some of the races we try to induce could probably also be
> done this way with code in the kernel to trigger the case we're worried
> about...

I am not wholly convinced. The primary purpose of the test suite is
prevent bugs of tomorrow, not to chase bugs of yesterday. If we focus too
much on bugs we have fixed, I worry we won't serendipitously detect bugs
early. Yes, bugs cluster and a mistake once made is likely to be made
again (so regression testing is vital) but I think we cross a line if
igt only exercises code written for conformance testing.

Yes to fault injection and the like. No to special conformance paths.

My 2p,
-Chris

--
Chris Wilson, Intel Open Source Technology Centre