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. -- Philippe. _______________________________________________ Xenomai mailing list [email protected] https://xenomai.org/mailman/listinfo/xenomai
