[Intel-gfx] [PATCH] drm/i915: Capture vma contents outside of spinlock

[Chris Wilson]

Quoting Matthew Auld (2019-07-25 22:04:33)
> On Thu, 25 Jul 2019 at 19:24, Chris Wilson <chris at chris-wilson.co.uk> wrote:
> >
> > Currently we use the engine->active.lock to ensure that the request is
> > not retired as we capture the data. However, we only need to ensure that
> > the vma are not removed prior to use acquiring their contents, and
> > since we have already relinquished our stop-machine protection, we
> > assume that the user will not be overwriting the contents before we are
> > able to record them.
> >
> > In order to capture the vma outside of the spinlock, we acquire a
> > reference and mark the vma as active to prevent it from being unbound.
> > However, since it is tricky allocate an entry in the fence tree (doing
> > so would require taking a mutex) while inside the engine spinlock, we
> > use an atomic bit and special case the handling for i915_active_wait.
> >
> > The core benefit is that we can use some non-atomic methods for mapping
> > the device pages, we can remove the slow compression phase out of atomic
> > context (i.e. stop antagonising the nmi-watchdog), and no we longer need
> > large reserves of atomic pages.
> >
> > Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=111215
> > Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
> > ---
> >  drivers/gpu/drm/i915/i915_active.c       |  34 ++++++-
> >  drivers/gpu/drm/i915/i915_active.h       |   3 +
> >  drivers/gpu/drm/i915/i915_active_types.h |   3 +
> >  drivers/gpu/drm/i915/i915_gpu_error.c    | 113 ++++++++++++++++-------
> >  4 files changed, 118 insertions(+), 35 deletions(-)
> 
> <snip>
> 
> >
> >  static struct drm_i915_error_object *
> > @@ -1370,6 +1399,7 @@ gem_record_rings(struct i915_gpu_state *error, struct compress *compress)
> >                 struct intel_engine_cs *engine = i915->engine[i];
> >                 struct drm_i915_error_engine *ee = &error->engine[i];
> >                 struct i915_request *request;
> > +               struct capture_vma *capture;
> 
> Not even setting capture = NULL?

gcc is a very forgiving compiler it seems. Well spotted,
-Chris