Re: [igt-dev] [PATCH i-g-t 1/6] test/perf: Drop caches when closing perf stream

Lionel Landwerlin
2020-03-04T08:45:58Z

On 04/03/2020 00:57, Umesh Nerlige Ramappa wrote:
> On Tue, Mar 03, 2020 at 02:38:08PM -0800, Umesh Nerlige Ramappa wrote:
>> Running ./build/tests/perf will run all the perf subtests in a sequence.
>> When running tests in a sequence, subsequent tests may not run with a
>> clean slate. For resources that are lazily released, drop caches in
>> __perf_close.
>
> Hi Lionel, Chris,
>
> I notice an issue on TGL when running the entire suite of perf tests.
> In my setup, the polling test was failing with invalid reports being
> seen in the beginning of the OA buffer. This issue is seen more
> prominently with the newly added subtests which call perf_open and
> perf_close a couple of times (say blocking-with-interrupt).
>
> What I see in some runs is that the second test would result in a
> bunch of unlanded reports in the beginning of the OA buffer. Assuming
> that we are already waiting for the NOA config with a noa_wait bo, I
> tried to look into this further.
>
> free_oa_buffer is called to free the oa_buffer bo and this work is
> deferred by the driver. If a test is called before this free
> completes, we see the issue. Just to test out this theory, if I
> comment out the free_oa_buffer entirely, I see that the tests pass
> without any issues since new gtt memory is being allocated each time.
>
> I guess the deferred free and the new allocation of the OA buffer for
> subsequent test has something missing. Maybe TLBs not being dropped? I
> imagine the OA unit might write valid reports somewhere based on what
> it sees in the TLBs and cpu is looking for them elsewhere (until the
> free completes). Just a theory though. Let me know what you think.
>
> For now igt_drop_caches_set(DROP_FREED) is what is helping and hence
> this patch.

Hey Umesh,

I guess this could be fixed by this commit :

commit 4b4e973d5eb89244b67d3223b60f752d0479f253
Author: Chris Wilson <chris@chris-wilson.co.uk>
Date:   Mon Mar 2 08:57:57 2020 +0000

drm/i915/perf: Reintroduce wait on OA configuration completion

If you can give this commit a try or rebase on drm-tip it would be great
to confirm.

Otherwise we might need more digging to figure what's going on.

Thanks,

-Lionel

>
> Thanks,
> Umesh
>
>>
>> Signed-off-by: Umesh Nerlige Ramappa <umesh.nerlige.ramappa@intel.com>
>> ---
>> tests/perf.c | 7 ++++++-
>> 1 file changed, 6 insertions(+), 1 deletion(-)
>>
>> diff --git a/tests/perf.c b/tests/perf.c
>> index 5e818030..189c6aa1 100644
>> --- a/tests/perf.c
>> +++ b/tests/perf.c
>> @@ -244,6 +244,12 @@ __perf_close(int fd)
>>         close(pm_fd);
>>         pm_fd = -1;
>>     }
>> +
>> +    /* When running tests in a sequence, subsequent tests may not
>> run with a
>> +     * clean slate. For resources that are lazily released, cleanup
>> here.
>> +     */
>> +    if (drm_fd >= 0 && !getgid() && !getuid())
>> +        gem_quiescent_gpu(drm_fd);
>> }
>>
>> static int
>> @@ -3993,7 +3999,6 @@ test_rc6_disable(void)
>>     igt_assert_eq(n_events_end - n_events_start, 0);
>>
>>     __perf_close(stream_fd);
>> -    gem_quiescent_gpu(drm_fd);
>>
>>     n_events_start = rc6_residency_ms();
>>     nanosleep(&(struct timespec){ .tv_sec = 1, .tv_nsec = 0 }, NULL);
>> --
>> 2.20.1
>>
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