On Fri, 23 Mar 2018 23:20:10 +0100 Matthias Schiffer <mschiffer@xxxxxxxxxxxxxxxxxxxx> wrote: > Hi, > I'm currently trying to debug a performance bottleneck on low-end ath79 > hardware running OpenWrt/LEDE, but it seems that ftrace is not working > correctly on these systems. I have tried this with recent 4.4.y and 4.9.y > with similar results; unfortunately, switching to a newer kernel is not > easily possible on this hardware at the moment. Please let me know if there > are any known issues or patches that I should backport. I don't know of any for mips (nothing in the git logs). The last updates to the mips code looks to be from 3.17. Also, I have no idea why try_to_get_module() would be crashing. > > There seem to be two separate issues: > > 1) Building with CONFIG_DYNAMIC_FTRACE leads to a kernel panic as soon as > kernel modules are loaded (logs attached). > > 2) function_graph tracer does not show anything useful: the trace output > looks like what was reported in [1]. Building with > CONFIG_FUNCTION_GRAPH_TRACER leads to a completely empty > trace_stat/function0 (except for the header); profiling is working as > expected when CONFIG_FUNCTION_GRAPH_TRACER is disabled. > > I would be thankful for any pointers that might help me to make this work. > > Kind regards, > Matthias > > > [1] https://www.linux-mips.org/archives/linux-mips/2014-11/msg00295.html >
