Re: [igt-dev] [PATCH i-g-t] tests/perf: add a test for OA data polling reads using "small" buffers

From: "Dixit, Ashutosh" <ashutosh.dixit@intel.com>
To: Lionel Landwerlin <lionel.g.landwerlin@intel.com>
Cc: igt-dev@lists.freedesktop.org
Subject: Re: [igt-dev] [PATCH i-g-t] tests/perf: add a test for OA data polling reads using "small" buffers
Date: Tue, 31 Mar 2020 00:48:45 -0700	[thread overview]
Message-ID: <871rp92cde.wl-ashutosh.dixit@intel.com> (raw)
In-Reply-To: <5fdba63f-3e17-7b20-663b-ffbe08294235@intel.com>

On Tue, 31 Mar 2020 00:36:54 -0700, Lionel Landwerlin wrote:
>
> On 31/03/2020 09:06, Dixit, Ashutosh wrote:
> > On Fri, 27 Mar 2020 12:49:22 -0700, Dixit, Ashutosh wrote:
> >> On Fri, 27 Mar 2020 12:06:13 -0700, Lionel Landwerlin wrote:
> >>> On 27/03/2020 21:03, Dixit, Ashutosh wrote:
> >>>> On Fri, 27 Mar 2020 09:09:41 -0700, Lionel Landwerlin wrote:
> >>>>> On 27/03/2020 06:50, Dixit, Ashutosh wrote:
> >>>>>> On Thu, 26 Mar 2020 21:42:50 -0700, Ashutosh Dixit wrote:
> >>>>>>> diff --git a/tests/perf.c b/tests/perf.c
> >>>>>>> index 724f6f809..3dc757c3b 100644
> >>>>>>> --- a/tests/perf.c
> >>>>>>> +++ b/tests/perf.c
> >>>>>>> +static void test_polling_small_buf(void)
> >>>>>>> +{
> >>>>>> /snip/
> >>>>>>
> >>>>>>> +
> >>>>>>> +	igt_assert(abs(n_expect_read_bytes - n_bytes_read) < (0.10 * n_expect_read_bytes));
> >>>>>>> +}
> >>>>>>> +
> >>>>>> I'd be wary of a 90% match on slow platforms like Atom? Maybe 80% is safer?
> >>>>> Do we have any experiment showing them behaving differently?
> >>>> No I don't have any data, but considering that in previous stable versions
> >>>> we can only read < 10% of the data, I think it should be ok to go down to
> >>>> 80%? So that we don't start getting unnecessary false alarms in CI, even
> >>>> when the issue is fixed.
> >>> Okay, for the record I get somewhere between 93~95% of expected reports on
> >>> KBLGT2.
> >> Yes I tried it and saw that. I already gave a R-b so we could probably
> >> merge the patch after making that change (0.2 instead of 0.1 above), or do
> >> you want me to post a new version with the change? Thanks!
> > Actually there has been some change in the kernel, earlier like you I was
> > also getting around 94% with a 1 KB buffer, now I am getting about
> > 87%. I am getting 94% with a 1 MB buffer. Does the amount of expected data
> > in the test need to be modified? I can try to bisect tomorrow and see what
> > has done this, unless you already know. Thanks!
>
> Ah, that's probably the read() bug you're fixing...
>
> Are you running with the kernel patch : "drm/i915/perf: Do not clear pollin
> for small user read buffers" ?

Yes, I was just testing the patch before posting it and I chanced on
this. Thanks!
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