On 07/06/2018 11:12 AM, Philippe Gerum wrote: > On 07/06/2018 11:09 AM, Federico Sbalchiero wrote: >> 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, >>> >> >> in the same configuration (kernel 3.18.20-ipipe + xenomai 3.0.7) >> dd if=/dev/zero of=/dev/null has almost no effect on latency. >> I think all data write to a few small buffers, not stressing L2 >> cache. >> > > You need to set a large block size for dd. > >
bs=16M suffices to raise the worst-case quite significantly on i.MX6QP (sabresd) here. -- Philippe. _______________________________________________ Xenomai mailing list [email protected] https://xenomai.org/mailman/listinfo/xenomai
