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

Lionel Landwerlin
2020-03-04T22:05:58Z

On 04/03/2020 19:51, Umesh Nerlige Ramappa wrote:
> On Wed, Mar 04, 2020 at 10:45:55AM +0200, Lionel Landwerlin wrote:
>> 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.
>
> I thought this commit was ensuring that the noa_wait is executed
> completely before we enable the OA buffer captures. That still does
> not explain why the issue goes away for me when I comment out
> free_oa_buffer.

If noa_wait is not waited upon, either from CPU or GPU, then we enable
OA while the configuration is not completely applied.

Hence the invalid data at the beginning of the buffer.

Are you saying this commit didn't help?

Thanks,

-Lionel

>
> Thanks,
> Umesh
>
>>
>> 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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>>
>>