Re: [igt-dev] [PATCH i-g-t 1/2] tests/gem_exec_await: Relax the busy spinner

From: Tvrtko Ursulin <tvrtko.ursulin@linux.intel.com>
To: Chris Wilson <chris@chris-wilson.co.uk>, igt-dev@lists.freedesktop.org
Cc: Intel-gfx@lists.freedesktop.org,
	Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Subject: Re: [igt-dev] [PATCH i-g-t 1/2] tests/gem_exec_await: Relax the busy spinner
Date: Mon, 19 Nov 2018 19:18:52 +0000	[thread overview]
Message-ID: <e45fe642-c384-8d74-4786-15e9a627490d@linux.intel.com> (raw)
In-Reply-To: <154264428448.24263.9411512811051111980@skylake-alporthouse-com>

On 19/11/2018 16:18, Chris Wilson wrote:
> Quoting Tvrtko Ursulin (2018-11-19 15:33:56)
>>
>> On 19/11/2018 15:28, Chris Wilson wrote:
>>> Quoting Tvrtko Ursulin (2018-11-19 15:22:28)
>>>> From: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
>>>>
>>>> Add some nop instructions between recursive batch buffer start calls to
>>>> give system some breathing room. Without these, especially when coupled
>>>> with memory pressure, false GPU hangs can be observed caused by the
>>>> inability of the chip to cope.
>>>
>>> Doesn't seem to be required. And the machines most susceptible to timer
>>> errors due to busyspin have not show the issue.
>>
>> With the memory pressure subtest, the second patch in this series, it
>> was make it or break it to have the nops. Without them it was GPU hangs
>> all around, and with them so far all clean.
> 
> First machine bsw, just applying patch 2/2,
> 
> IGT-Version: 1.23-gb6b8d829 (x86_64) (Linux: 4.20.0-rc2+ x86_64)
> Using Execlists submission
> Ring size: 131 batches
> Starting subtest: wide-all
> wide: 420 cycles: 24121.034us
> Subtest wide-all: SUCCESS (47.060s)
> Starting subtest: wide-contexts
> wide: 340 cycles: 24893.896us
> Subtest wide-contexts: SUCCESS (22.265s)
> Starting subtest: wide-contexts-mempressure
> wide: 232 cycles: 25153.899us
> Subtest wide-contexts-mempressure: SUCCESS (23.141s)
> 
> :|

Yes, I think what I had before I cleaned up the test case was more 
copy&paste of the memory pressure thread from gem_syslatency - including 
the rtprio and multithreadedness. So I was possibly starving the 
tasklets and who knows what not, as well as applying memory pressure. 
However, fact still is adding nops to the spinner made even that monster 
pass repeatedly. I'll play with it more tomorrow.

Regards,

Tvrtko
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