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

[Jesse Barnes <jbarnes@virtuousgeek.org>]

On 03/03/2015 04:06 PM, Daniel Vetter wrote:
> On Tue, Mar 3, 2015 at 10:15 PM, Chris Wilson <chris@chris-wilson.co.uk> wrote:
>> 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.
> 
> Also swapping tests are a solved problem really, we've had an "mlock
> most of mem" todo since years and Thomas Wood is implementing it. Well
> it's committed for gem_tiled_swapping already
> 
> commit 42b02c284ed24871528df8f1b3eaad7fe1554fd9
> Author: Thomas Wood <thomas.wood@intel.com>
> Date:   Mon Dec 8 11:12:51 2014 +0000
> 
>     lib: add a function to lock memory into RAM
> 
> what's missing is rolling this out for other tests.
> 
> Now I love igt bashing as much as the next person, but maybe check
> occasionally whether your rant-du-jour is still relevant ...

My "rant du jour" still is.  mlock() is a good solution for some things,
but for the simple task of testing kernel swap out code, just running
that code is the most straightforward thing to do, rather than trying to
contort into it from userspace.

Jesse

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