[Xenomai] i.MX6q memory write causes high latency

Federico Sbalchiero f.sbalchiero at sferapro.com
Thu Jul 5 11:50:58 CEST 2018


Il 05/07/2018 11:14, Philippe Gerum ha scritto:
> On 07/04/2018 07:06 PM, Federico Sbalchiero wrote:
>> Hi,
>> first I want to say thanks to everyone involved in Xenomai for their job.
>>
>> I'm testing Xenomai 3.0.7 and ipipe-arm/4.14 on Freescale/NXP i.MX6q
>> sabresd board using Yocto. System boots fine and is stable, but latency
>> under load (xeno-test) is higher than in my reference system (Xenomai
>> 2.6.5 on Freescale kernel 3.10.17 + ipipe 3.10.18).
>> This is after disabling power management, frequency scaling, CMA,
>> graphics, tracing, debug.
>>
>> I have found that a simple non-realtime user space process writing a
>> buffer in memory (memwrite) is able to trigger such high latencies.
>> Latency worsen a lot running a copy of the process on each core.
>> There is a correlation between buffer size and cache size suggesting
>> an L2 cache issue, like the L2 write allocate discussed in the mailing
>> list, but I can confirm L2 WA is disabled (see log).
>>
>> I'm looking for comments or suggestions.
>>
> A basic dd if=/dev/zero of=/dev/null loop in the background is enough to
> raise the latency actually. Could you try the Xenomai 3 + 3.18 combo on
> your hw and let us know whether you see the same regression?
>
> TIA,
>
Yes, I'll try it this evening (out of office today).



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