Re: [igt-dev] [CI i-g-t] tests/perf_pmu: Avoid RT thread for accuracy test

From: Tvrtko Ursulin <tvrtko.ursulin@linux.intel.com>
To: Chris Wilson <chris@chris-wilson.co.uk>,
	Tvrtko Ursulin <tursulin@ursulin.net>,
	igt-dev@lists.freedesktop.org
Cc: Intel-gfx@lists.freedesktop.org
Subject: Re: [igt-dev] [CI i-g-t] tests/perf_pmu: Avoid RT thread for accuracy test
Date: Mon, 26 Mar 2018 13:40:19 +0100	[thread overview]
Message-ID: <d596b0d7-14c5-8daf-8a9b-75895575e9a3@linux.intel.com> (raw)
In-Reply-To: <152206306117.4115.14045420465858687009@mail.alporthouse.com>

On 26/03/2018 12:17, Chris Wilson wrote:
> Quoting Tvrtko Ursulin (2018-03-26 11:57:58)
>>   * No self-adjust - instead just report the achieved cycle and let the
>>     parent check against it.
> 
> Sniff, I was rather proud of our achievement. I had it in mind as a
> template for future autocalibration routines. Is it really useless
> overengineering, or worse broken?

It works fine I think, but the problem is I cannot locate a source of 
systematic error which seems proportional to number of loop iterations. 
:( After battling with trying to improve it for a couple days I decided 
to try to see how the simpler approach will fare on the shards.

There's the tasklet delay, which made me think things could be better 
without RT. And then polling on the spinner makes it worse in all cases 
for me, however I fiddle with it. So again, I wanted to try the 
simplification..

The version from this patch seems super stable on my system, but the 50% 
case still has an apparent +.5-6% systematic error. Maybe on the shards 
it will not be as stable..

Regards,

Tvrtko
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