Le 17/04/2014 22:38, Stanislav Meduna a écrit : > Hi, > > on a i.MX28: > > Linux nxt 3.12.15-rt25+ #83 PREEMPT RT Thu Apr 17 20:54:00 CEST 2014 armv5tejl GNU/Linux > > (...) > > Maybe it is just some tracing infrastructure interference - the effect > of enabling the tracing is huge on this platform for some reason. > Just enabling the irqsoff tracing makes the machine unsuitable > for any serious load. For the record, latencies on imx28 are high because: 1- it has an arm926 core, which uses a VIVT cache, and Linux chooses to flush cache at each mm switch to avoid aliasing issues; 2- the arm926 idle routine, in order to work around a hardware bug flushes the instruction cache before calling the "wfi" instruction. #2 can be avoided by using nohlt #1 can be avoided by using the ARM FCSE extension. A patch exists for #1 which is currently integrated into the Adeos patch but could exist independently. I could post the patch here for Linux vanilla here if there is enough interest, and let you do the merge with the preempt_rt patch. Regards. -- Gilles. -- To unsubscribe from this list: send the line "unsubscribe linux-rt-users" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
