[Intel-gfx] [PATCH 2/2] drm/i915: Embellish wait_end trace

[Chris Wilson]

On Tue, Jul 29, 2014 at 01:14:30PM -0700, Ben Widawsky wrote:
> This adds two new data points to the trace event, wait time, and whether
> or not the event slept. Both of these should already be obtainable
> through various means. This patch just makes the data more accessible.

Right, the key point is that since the advent of the wait_begin/_end
pair is that we now allow concurrent non-blocking waits.
 
> Wait is obtainable with the current code by matching seqnos in
> begin/end. In simple cases where begin/ends are always paired, this is
> trivial. However, if you queue up multiple begins/ends, it can get
> confusing. We're already calculating wait time, so it's trivially added
> here. This patch also provides the slightly more accurate wait_time as
> opposed to the timestamps from the tracepoint. It's observable, but just
> noise.
> 
> The second bit of information, whether or not the operation slept is
> helpful in determining where time went. This is probably also obtainable
> through the scheduler events. However, we have the information easily at
> our fingertips, we may as well give it out.
> 
> This results in an event which looks like:
> gem_gtt_hog   409 [000]    32.012641: i915:i915_gem_request_wait_end: dev=0, ring=3, seqno=4294963203, duration=0.000368225 (slept=yes)
> 
> While here, rename sleep_time to wait_time since the verb sleep hasn't
> been true for a long time (several conditions exist where it won't
> sleep).
> 
> Signed-off-by: Ben Widawsky <ben at bwidawsk.net>

Other than the debate in the earlier patch, this looks fine.
-Chris

-- 
Chris Wilson, Intel Open Source Technology Centre