Re: [PATCH] drm/i915: Add a tracepoint for using a semaphore

["Ville Syrjälä" <ville.syrjala@linux.intel.com>]

On Wed, Sep 25, 2013 at 11:43:28AM +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!
> 
> v2: Rebrand it as a ring event, rather than an object event.
> v3: Include the seqno in the tracepoint for posterity or something.
> 
> Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
> ---
>  drivers/gpu/drm/i915/i915_gem.c   |  1 +
>  drivers/gpu/drm/i915/i915_trace.h | 26 ++++++++++++++++++++++++++
>  2 files changed, 27 insertions(+)
> 
> diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c
> index 82bc029..fa3b373 100644
> --- a/drivers/gpu/drm/i915/i915_gem.c
> +++ b/drivers/gpu/drm/i915/i915_gem.c
> @@ -2625,6 +2625,7 @@ i915_gem_object_sync(struct drm_i915_gem_object *obj,
>  	if (ret)
>  		return ret;
>  
> +	trace_i915_gem_ring_sync_to(from, to, seqno);
>  	ret = to->sync_to(to, from, seqno);

Passing the rings in the same order to both might avoid some confusion,
but I don't care enough to withhold my r-b so:
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>

>  	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 daa6fdf..6e580c9 100644
> --- a/drivers/gpu/drm/i915/i915_trace.h
> +++ b/drivers/gpu/drm/i915/i915_trace.h
> @@ -248,6 +248,32 @@ TRACE_EVENT(i915_gem_evict_vm,
>  	    TP_printk("dev=%d, vm=%p", __entry->vm->dev->primary->index, __entry->vm)
>  );
>  
> +TRACE_EVENT(i915_gem_ring_sync_to,
> +	    TP_PROTO(struct intel_ring_buffer *from,
> +		     struct intel_ring_buffer *to,
> +		     u32 seqno),
> +	    TP_ARGS(from, to, seqno),
> +
> +	    TP_STRUCT__entry(
> +			     __field(u32, dev)
> +			     __field(u32, sync_from)
> +			     __field(u32, sync_to)
> +			     __field(u32, seqno)
> +			     ),
> +
> +	    TP_fast_assign(
> +			   __entry->dev = from->dev->primary->index;
> +			   __entry->sync_from = from->id;
> +			   __entry->sync_to = to->id;
> +			   __entry->seqno = seqno;
> +			   ),
> +
> +	    TP_printk("dev=%u, sync-from=%u, sync-to=%u, seqno=%u",
> +		      __entry->dev,
> +		      __entry->sync_from, __entry->sync_to,
> +		      __entry->seqno)
> +);
> +
>  TRACE_EVENT(i915_gem_ring_dispatch,
>  	    TP_PROTO(struct intel_ring_buffer *ring, u32 seqno, u32 flags),
>  	    TP_ARGS(ring, seqno, flags),
> -- 
> 1.8.4.rc3
> 
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-- 
Ville Syrjälä
Intel OTC