[igt-dev] [PATCH i-g-t 1/1] i915_pm_rpm: gem-execbuf-stress-extra-wait faster

[Chris Wilson]

Quoting Caz Yokoyama (2019-03-05 23:22:06)
> On Tue, 2019-03-05 at 17:22 +0000, Chris Wilson wrote:
> > Quoting Caz Yokoyama (2019-03-06 00:06:55)
> > > Less iterate because WAIT_EXTRA adds extra 5 sec delay for each
> > > iteration.
> > > This test is similar to gem-execbuf-stress except for WAIT_EXTRA.
> > > It runs 86 sec. while gem-execbuf-stress runs 38 sec.
> > > i.e. 38s + iteration(rounds,10) * 5s = 88s
> > 
> > Why does it wait for 5s? There's no second stage to runtime suspend,
> > but
> > if there was, add a debug interface to force it.
> I believe no because teardown_environment() is the onlye statement
> after igt_subtest("gem-execbuf-stress-extra-wait").

I mean in the kernel. I can't think what the extra 5s does, my guess
would be that it was to try and induce some HW change. (But by the time
runtime suspend completes, the HW *should* be as powered down as we can
achieve.)

Something that may help a bit is by adding something like
pm_runtime_force_suspend() to a debug path, like DROP_SUSPEND.

> > Something else that can be employed to speed up this test would be
> > igt_drop_caches_set(DROP_IDLE) (before waiting for runtime suspend).
> Yes, it does speed up to 56sec from 88sec. Not only gem-execbuf-stress-
> extra-wait, but also other 2 tests speed up. For example, gem-execbuf-
> stress speed up to 9sec from 38sec. Thank you.
> 
> How do you want to have patches? Only igt_drop_caches_set(DROP_IDLE)?
> Both igt_drop_caches_set(DROP_IDLE) and rounds / 2 in a single patch?
> Separate 2 patches?

2 patches. Adding DROP_IDLE is definitely a functional change (that
should have no impact on behaviour) that wants to be separate. Doing
exactly the same operations faster is one thing; doing fewer operations
altogether requires some more handwaving as why you think that is
justified, and why that is important enough to take a risk.
-Chris