[Intel-gfx] [PATCH 1/2] drm/i915: Warn if request allocation stalls

[Chris Wilson]

Quoting Tvrtko Ursulin (2018-10-05 09:37:37)
> 
> On 05/10/2018 09:02, Chris Wilson wrote:
> > Add a warning for an allocation stall to make it painfully more obvious
> > while debugging.
> > 
> > Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
> > ---
> >   drivers/gpu/drm/i915/i915_gem.h     | 2 ++
> >   drivers/gpu/drm/i915/i915_request.c | 6 ++++++
> >   2 files changed, 8 insertions(+)
> > 
> > diff --git a/drivers/gpu/drm/i915/i915_gem.h b/drivers/gpu/drm/i915/i915_gem.h
> > index 599c4f6eb1ea..e2db030fd75a 100644
> > --- a/drivers/gpu/drm/i915/i915_gem.h
> > +++ b/drivers/gpu/drm/i915/i915_gem.h
> > @@ -47,6 +47,7 @@ struct drm_i915_private;
> >   #define GEM_DEBUG_DECL(var) var
> >   #define GEM_DEBUG_EXEC(expr) expr
> >   #define GEM_DEBUG_BUG_ON(expr) GEM_BUG_ON(expr)
> > +#define GEM_DEBUG_WARN(expr...) WARN(expr)
> 
> Reminds me of one patch which would look so good preceding this one!
> 
> >   
> >   #else
> >   
> > @@ -58,6 +59,7 @@ struct drm_i915_private;
> >   #define GEM_DEBUG_DECL(var)
> >   #define GEM_DEBUG_EXEC(expr) do { } while (0)
> >   #define GEM_DEBUG_BUG_ON(expr)
> > +#define GEM_DEBUG_WARN(expr...) do { } while (0)
> >   #endif
> >   
> >   #if IS_ENABLED(CONFIG_DRM_I915_TRACE_GEM)
> > diff --git a/drivers/gpu/drm/i915/i915_request.c b/drivers/gpu/drm/i915/i915_request.c
> > index abd4dacbab8e..32bf2c9868bf 100644
> > --- a/drivers/gpu/drm/i915/i915_request.c
> > +++ b/drivers/gpu/drm/i915/i915_request.c
> > @@ -647,6 +647,8 @@ i915_request_alloc(struct intel_engine_cs *engine, struct i915_gem_context *ctx)
> >       rq = kmem_cache_alloc(i915->requests,
> >                             GFP_KERNEL | __GFP_RETRY_MAYFAIL | __GFP_NOWARN);
> >       if (unlikely(!rq)) {
> > +             GEM_DEBUG_DECL(ktime_t start = ktime_get());
> > +
> >               i915_retire_requests(i915);
> >   
> >               /* Ratelimit ourselves to prevent oom from malicious clients */
> > @@ -671,6 +673,10 @@ i915_request_alloc(struct intel_engine_cs *engine, struct i915_gem_context *ctx)
> >                       ret = -ENOMEM;
> >                       goto err_unreserve;
> >               }
> > +
> > +             GEM_DEBUG_WARN(ktime_ms_delta(ktime_get(), start) > 500,
> > +                            "request allocation delayed for %lldms\n",
> > +                            ktime_ms_delta(ktime_get(), start));
> 
> Usefulness of the arbitrary threshold vs source code pollution?

I'm just trying to prove that the hang is here, so purely for debugging
purposes.
-Chris