Re: [PATCH i-g-t] tests/pm_rpm: Fix CRASH on machines that lack LLC

[Imre Deak <imre.deak@intel.com>]

On ke, 2016-03-02 at 14:37 +0000, Chris Wilson wrote:
> On Wed, Mar 02, 2016 at 04:32:41PM +0200, Imre Deak wrote:
> > On ke, 2016-03-02 at 14:04 +0000, Chris Wilson wrote:
> > > On Wed, Mar 02, 2016 at 03:55:56PM +0200, David Weinehall wrote:
> > > > On Wed, Mar 02, 2016 at 01:27:06PM +0000, Chris Wilson wrote:
> > > > > On Wed, Mar 02, 2016 at 03:11:57PM +0200, David Weinehall
> > > > > wrote:
> > > > > > On machines that lack an LLC the pm-caching subtest will
> > > > > > terminate with sigbus and thus CRASH during the
> > > > > > I915_CACHING_CACHED iteration.  This patch adds a check for
> > > > > > this condition and skips that iteration.
> > > > > 
> > > > > you can delete the got_caching assertion and
> > > > > enable_one_screen_and_wait() as well, they are not exercising
> > > > > the
> > > > > associated code.
> > > > 
> > > > Hmmm.  How about the matching disable_all_screens_and_wait()?
> > > > Also, isn't the got_caching assertion meant to check that
> > > > when we enable GEM caching we actually get the mode we
> > > > requested,
> > > > and if so, do we test for this elsewhere? Or are you saying
> > > > that
> > > > this test doesn't achieve this purpose?
> > > 
> > > This is not a test for set-caching API, but on whether we do
> > > device
> > > accesses without rpm. get-caching doesn't touch the device at all
> > > (and
> > > never ever should) so is irrelevant for the test.
> > 
> > The purpose of the enable/disable screen calls was to make sure
> > that
> > the object gets unbound, otherwise we may not call i915_vma_bind()
> > which is where the actual HW access happened. But actually it would
> > be
> > enough to call disable_all_screens_and_wait() once and then call
> > wait_for_suspended() instead of disable_all_screens_and_wait() in
> > the
> > loop.
> 
> Actually no, that's why you have the memset/*ptr - that is what
> forces
> the vma to get bound. And to exercise the set-cache-level, you need
> it
> bound into at a different cache-level, hence the suggestion to call
> set-cache-level again - respecting the rules of using the GGTT.

Yes I see that it gets bound, but is guaranteed that it gets unbound
during the next set-cache-level call? As I understand it will only
happen if i915_gem_valid_gtt_space() returns false.

--Imre
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