* Robert Johnson | 2014-03-17 17:41:25 [+0000]: >I am using an embedded single board computer (SBC) that has a Freescale P2020 processor. The vendor board support package (BSP) for this product currently uses a 3.0.4 Linux kernel. In looking through the RT patch for various Linux kernel versions even up through 3.12.13-rt21, I see that CONFIG_HIGHMEM is not allowed if CONFIG_PREEMPT_RT_FULL is selected (see arch/powerpc/Kconfig). > >The result for my SBC is that if I enable CONFIG_PREEMPT_RT_FULL in the kernel, I am then only able to access 1GB of RAM instead of the 4GB that is resident. For 2 GiB you could move the memory mapping to something like 1.5GiB userland, 2.GiB kernel and the remaining 500MiB for virtual. >Is there any way to get CONFIG_PREEMPT_RT_FULL to work with CONFIG_HIGHMEM? Yes. The trick is to look either at the ARM code or at the x86 code and do something similar for powerpc. >If I want to use CONFIG_HIGHMEM, should I consider the use of CONFIG_PREEMPT_RTB which does not appear to have a dependency? You could CONFIG_PREEMPT_RT_BASE with CONFIG_HIGHMEM, yes. But then don't complain about your latency which will be higher compared to _FULL. Again: CONFIG_PREEMPT_RT_BASE is only debugging option. Sebastian -- 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
