Re: [PATCH 1/2] drm/i915/tracepoints: Don't compile-out low-level tracepoints

From: "Rogozhkin, Dmitry V" <dmitry.v.rogozhkin@intel.com>
To: "chris@chris-wilson.co.uk" <chris@chris-wilson.co.uk>
Cc: "intel-gfx@lists.freedesktop.org" <intel-gfx@lists.freedesktop.org>
Subject: Re: [PATCH 1/2] drm/i915/tracepoints: Don't compile-out low-level tracepoints
Date: Mon, 11 Sep 2017 20:23:36 +0000	[thread overview]
Message-ID: <1505132440.7679.7.camel@intel.com> (raw)
In-Reply-To: <150515953310.22039.1236116771628826548@mail.alporthouse.com>

On Mon, 2017-09-11 at 20:52 +0100, Chris Wilson wrote:
> Quoting Tvrtko Ursulin (2017-09-11 16:34:08)
> > 
> > On 11/09/2017 14:09, Michał Winiarski wrote:
> > > There's no reason to hide those tracepoints.
> > > Let's also remove the DRM_I915_LOW_LEVEL_TRACEPOINTS Kconfig option.
> > 
> > No numbers from (micro-)bechmarks showing how small the impact of doing 
> > this is? I thought John was compiling this data. It will be just a no-op 
> > on the fast path, but a bit more generated code.
> > 
> > Assuming that will be fine, the only potentially problematic aspect that 
> > comes to mind is the fact meaning of these tracepoints is a bit 
> > different between execlists and guc. But maybe that is thinking to low 
> > level (!) - in fact they are in both cases at points where i915 is 
> > passing/receiving requests to/from hardware so not an issue?
> 
> Along the same lines is that this implies that these are important
> enough to be ABI, and that means we need to make a long term decision on
> the viability and meaning of such tracepoints.
> -Chris
There is a number of applications which use these tracepoints for tasks
profiling putting them on the time scale for visualization. For example,
VTune and GPA, - these 2 are closed source. Not sure whether there are
open source profiling tools with such support (at least for GPU). Right
now VTune and GPA are stuck with custom patches for the i915 in the
better case, thus limiting themselves with the customers who are ok with
the custom patching. Thus, making this ABI (if possible) or at least
making sure this does not get broken or disappears (with for example GUC
enabling) would be highly beneficial.

Dmitry.

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