Em Mon, Jan 26, 2015 at 01:51:23PM +0000, Russell King - ARM Linux escreveu: > On Mon, Jan 26, 2015 at 10:27:11AM +0000, Will Deacon wrote: > > On Sun, Jan 25, 2015 at 03:56:52PM +0000, Russell King - ARM Linux wrote: > > > On Sat, Jan 24, 2015 at 04:23:42PM -0600, Felipe Balbi wrote: > > > > yeah, I'll try a few older kernels, also see if I can reproduce on other > > > > boards.
> > > Perf works for me with CONFIG_FRAME_POINTER=y, but that's only for kernel > > > space, and for userspace where the programs have been built for ARM mode > > > with frame pointers. > > > The kernel may work without CONFIG_FRAME_POINTER set, but I've never > > > tested that, and I'd suggest that (given my experience looking at oops > > > dumps) it's not all that reliable. > > > Lastly, userspace without frame pointers is pretty much hopeless. > > FWIW, perf can now use libunwind for unwinding the userspace side of > > things, so it's not quite as bad as it used to be. For the kernel side, > > if the unwinder isn't working properly it would be nice to know *why*, > > but I agree that it tends to be far flakier than the frame-pointer method. > I don't see how userspace could be unwound without capturing the entire > userspace stack on every perf event - and that could be a considerable > size. We have no way to know within the kernel which words on the That is what you can do using 'perf record --call-graph dwarf': -g enables call-graph recording --call-graph <mode[,dump_size]> setup and enables call-graph (stack chain/backtrace) recording: fp dwarf That will use: PERF_SAMPLE_REGS_USER = 1U << 12, PERF_SAMPLE_STACK_USER = 1U << 13, struct perf_event_attr { <SNIP> /* * Defines set of user regs to dump on samples. * See asm/perf_regs.h for details. */ __u64 sample_regs_user; /* * Defines size of the user stack to dump on samples. */ __u32 sample_stack_user; <SNIP> } > userspace stack are part of the callchain and which aren't - the only > way we'd know is by loading the userspace's unwind tables, having the > kernel parsing them and generate a list of functions. Or deferring it to userspace to do that later. - Arnaldo -- To unsubscribe from this list: send the line "unsubscribe linux-omap" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html