[igt-dev] [PATCH i-g-t 1/4] i915/perf_pmu: Verify RC6 measurements before/after suspend

[Chris Wilson]

Quoting Tvrtko Ursulin (2020-12-14 16:08:34)
> 
> On 14/12/2020 15:49, Chris Wilson wrote:
> > Quoting Tvrtko Ursulin (2020-12-14 15:42:20)
> >>
> >> On 14/12/2020 10:51, Chris Wilson wrote:
> >>> RC6 should work before suspend, and continue to increment while idle
> >>> after suspend. Should.
> >>>
> >>> v2: Include a longer sleep after suspend; it appears we are reticent to
> >>> idle so soon after waking up.
> >>>
> >>> Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
> >>> Cc: Tvrtko Ursulin <tvrtko.ursulin at intel.com>
> >>> ---
> >>>    tests/i915/perf_pmu.c | 28 +++++++++++++++++++++++++---
> >>>    1 file changed, 25 insertions(+), 3 deletions(-)
> >>>
> >>> diff --git a/tests/i915/perf_pmu.c b/tests/i915/perf_pmu.c
> >>> index cb7273142..0b470c1bc 100644
> >>> --- a/tests/i915/perf_pmu.c
> >>> +++ b/tests/i915/perf_pmu.c
> >>> @@ -170,6 +170,7 @@ static unsigned int measured_usleep(unsigned int usec)
> >>>    #define TEST_RUNTIME_PM (8)
> >>>    #define FLAG_LONG (16)
> >>>    #define FLAG_HANG (32)
> >>> +#define TEST_S3 (64)
> >>>    
> >>>    static igt_spin_t * __spin_poll(int fd, uint32_t ctx,
> >>>                                const struct intel_execution_engine2 *e)
> >>> @@ -1578,7 +1579,7 @@ test_frequency_idle(int gem_fd)
> >>>                     "Actual frequency should be 0 while parked!\n");
> >>>    }
> >>>    
> >>> -static bool wait_for_rc6(int fd)
> >>> +static bool wait_for_rc6(int fd, int timeout)
> >>>    {
> >>>        struct timespec tv = {};
> >>>        uint64_t start, now;
> >>> @@ -1594,7 +1595,7 @@ static bool wait_for_rc6(int fd)
> >>>                now = pmu_read_single(fd);
> >>>                if (now - start > 1e6)
> >>>                        return true;
> >>> -     } while (!igt_seconds_elapsed(&tv));
> >>> +     } while (igt_seconds_elapsed(&tv) <= timeout);
> >>>    
> >>>        return false;
> >>>    }
> >>> @@ -1636,14 +1637,32 @@ test_rc6(int gem_fd, unsigned int flags)
> >>>                }
> >>>        }
> >>>    
> >>> -     igt_require(wait_for_rc6(fd));
> >>> +     igt_require(wait_for_rc6(fd, 1));
> >>>    
> >>>        /* While idle check full RC6. */
> >>>        prev = __pmu_read_single(fd, &ts[0]);
> >>>        slept = measured_usleep(duration_ns / 1000);
> >>>        idle = __pmu_read_single(fd, &ts[1]);
> >>> +
> >>>        igt_debug("slept=%lu perf=%"PRIu64"\n", slept, ts[1] - ts[0]);
> >>> +     assert_within_epsilon(idle - prev, ts[1] - ts[0], tolerance);
> >>> +
> >>> +     if (flags & TEST_S3) {
> >>> +             prev = __pmu_read_single(fd, &ts[0]);
> >>> +             igt_system_suspend_autoresume(SUSPEND_STATE_MEM,
> >>> +                                           SUSPEND_TEST_NONE);
> >>> +             idle = __pmu_read_single(fd, &ts[1]);
> >>> +             igt_debug("suspend=%"PRIu64"\n", ts[1] - ts[0]);
> >>> +             //assert_within_epsilon(idle - prev, ts[1] - ts[0], tolerance);
> >>> +     }
> >>> +
> >>> +     igt_assert(wait_for_rc6(fd, 5));
> >>>    
> >>> +     prev = __pmu_read_single(fd, &ts[0]);
> >>> +     slept = measured_usleep(duration_ns / 1000);
> >>> +     idle = __pmu_read_single(fd, &ts[1]);
> >>> +
> >>> +     igt_debug("slept=%lu perf=%"PRIu64"\n", slept, ts[1] - ts[0]);
> >>
> >> You plan to leave the C++ bit commented out above and just check it
> >> here? Doesn't seem it harms to check twice in the non-S3 case anyway,
> >> just asking.
> > 
> > My expectation is that we should have a momentary blip !rc6 during
> > suspend, and so across suspend we should find mono_raw ~= rc6
> > 
> > However, since it is taking a few seconds for us to start rc6 again
> > after resume, that clearly fails. I'm not sure why it takes so long, so
> > I suspect a bug. (Possibly something like we are not entering rc6 until
> > a heartbeat after resume????)
> > 
> > So the // is my expectation; the current test the reality.
> > How best to document that?
> 
> CPU clock is stopped and we expect RC6 to be stopped but we probably 
> cannot be certain enough of the error between the two. So now I am not 
> sure we will every be able to rely on it matching close enough.
> 
> How do the absolute cpu ts and rc6 values look after resume, and both 
> relative to pre-suspend? Do they not see the S3 as expected but just rc6 
> is not increasing for how long?

Right, suspend time is absent from the timestamps. rc6 does not start
ticking again for ~3s. Smells like a heartbeat :(
-Chris