[Intel-gfx] [PATCH] drm/i915: Add a tracepoint for using a semaphore

[Ville Syrjälä]

On Mon, Aug 26, 2013 at 01:46:21PM +0100, Chris Wilson wrote:
> So that we can find the callers who introduce a ring stall. A single
> ring stall is not too unwelcome, the right issue becomes when they start
> to interlock and prevent any concurrent work. That, however, is a little
> tricker to detect with a mere tracepoint!

I was staring at the semaphore code a bit recently, and I was wondering
if it would make sense to do a manual seqno check (against the ring's
current seqno, not just the last sync_seqno) before we decide to
add the semaphore into the ring?

> 
> Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
> ---
>  drivers/gpu/drm/i915/i915_gem.c   |  2 ++
>  drivers/gpu/drm/i915/i915_trace.h | 19 +++++++++++++++++++
>  2 files changed, 21 insertions(+)
> 
> diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c
> index 85537d1..0122278 100644
> --- a/drivers/gpu/drm/i915/i915_gem.c
> +++ b/drivers/gpu/drm/i915/i915_gem.c
> @@ -2698,6 +2698,8 @@ i915_gem_object_sync(struct drm_i915_gem_object *obj,
>  	if (ret)
>  		return ret;
>  
> +	trace_i915_gem_object_sync(obj, to);
> +
>  	ret = to->sync_to(to, from, seqno);
>  	if (!ret)
>  		/* We use last_read_seqno because sync_to()
> diff --git a/drivers/gpu/drm/i915/i915_trace.h b/drivers/gpu/drm/i915/i915_trace.h
> index feaacbb..728c43b 100644
> --- a/drivers/gpu/drm/i915/i915_trace.h
> +++ b/drivers/gpu/drm/i915/i915_trace.h
> @@ -33,6 +33,25 @@ TRACE_EVENT(i915_gem_object_create,
>  	    TP_printk("obj=%p, size=%u", __entry->obj, __entry->size)
>  );
>  
> +TRACE_EVENT(i915_gem_object_sync,
> +	    TP_PROTO(struct drm_i915_gem_object *obj, struct intel_ring_buffer *to),
> +	    TP_ARGS(obj, to),
> +
> +	    TP_STRUCT__entry(
> +			     __field(struct drm_i915_gem_object *, obj)
> +			     __field(u32, sync_from)
> +			     __field(u32, sync_to)
> +			     ),
> +
> +	    TP_fast_assign(
> +			   __entry->obj = obj;
> +			   __entry->sync_from = obj->ring->id;
> +			   __entry->sync_to = to->id;
> +			   ),
> +
> +	    TP_printk("obj=%p, sync-from=%u, sync-to=%u", __entry->obj, __entry->sync_from, __entry->sync_to)
> +);
> +
>  TRACE_EVENT(i915_vma_bind,
>  	    TP_PROTO(struct i915_vma *vma, bool mappable),
>  	    TP_ARGS(vma, mappable),
> -- 
> 1.8.4.rc3
> 
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-- 
Ville Syrjälä
Intel OTC