[igt-dev] [PATCH i-g-t] i915/i915_pm_rpm: Only check for suspend failures after each debugfs entry

[Chris Wilson]

Quoting Martin Peres (2020-02-21 08:28:16)
> On 2020-02-21 10:21, Chris Wilson wrote:
> > Quoting Martin Peres (2020-02-21 07:33:59)
> >> On 2020-02-20 19:41, Chris Wilson wrote:
> >>> Since we check before and then after each debugfs entry, we do not need
> >>> to check before each time as well. We will error out as soon as it does
> >>> fail, at all other times we know the system to be idle.
> >>>
> >>> No impact on runtime for glk (which apparently is one of the better
> >>> behaving systems).
> >>>
> >>> Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
> >>> Cc: Martin Peres <martin.peres at linux.intel.com>
> >>
> >> I don't like this patch because the first read might not have the gpu
> >> suspended, and there shouldn't be much overhead in checking twice rather
> >> than once.
> >>
> >> What's your rationale here?
> > 
> > We always do a check before after each file. We start in a known state,
> > and expect to be able to return to that suspended state, and the _real_
> > guts of the test is that any device access is accounted for.
> > 
> > assert(suspended) would be a better check for non-interference.
> 
> I would feel better with assert(suspended) added, but would it really
> speed anything up since I assume wait_for_suspended() should be
> instantaneous if we are already suspended, right?

No, only if there was some random bug, we would now get a failure rather
than papering it over.
-Chris