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 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. -- FTTC broadband for 0.8mile line: currently at 10.5Mbps down 400kbps up according to speedtest.net. -- To unsubscribe from this list: send the line "unsubscribe linux-omap" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
