From mboxrd@z Thu Jan 1 00:00:00 1970 From: jamie@jamieiles.com (Jamie Iles) Date: Thu, 11 Nov 2010 12:21:43 +0000 Subject: [Questions] How to run 'perf top' on ARM to profile kernel functions with modules loaded In-Reply-To: <1289477176.2084.64.camel@laptop> References: <20101111091733.GA2929@pulham.picochip.com> <1289477176.2084.64.camel@laptop> Message-ID: <20101111122143.GF2929@pulham.picochip.com> To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org On Thu, Nov 11, 2010 at 01:06:16PM +0100, Peter Zijlstra wrote: > On Thu, 2010-11-11 at 09:17 +0000, Jamie Iles wrote: > > On Thu, Nov 11, 2010 at 03:52:07PM +0800, Ming Lei wrote: > > > 2010/11/11 Ming Lei : > > > > Hi, > > > > > > > > 'perf top' can't display any functions when modules are loaded on ARM. > > > > > > Sorry, should be can't display any kernel functions when modules are loaded > > > on ARM. > > I've noticed this myself and I spent a bit of time looking into it last week > > but didn't get too far. I did wonder if it was something to do with the map > > fixups after loading the modules. If you look at the raw events after a perf > > record with 'perf report -D' then the last module has a size that takes it to > > 0xFFFFFFFF which overlaps with the rest of the kernel symbols. > > > > On x86 it looks like the modules are loaded after the kernel image in VM > > unlike ARM. > > Order shouldn't matter, but that overlap is very likely what kills it. > That module size is buggy. I'm guessing that its in util/symbol.c:__map_groups__fixup_end(): for (nd = rb_next(prevnd); nd; nd = rb_next(nd)) { prev = curr; curr = rb_entry(nd, struct map, rb_node); prev->end = curr->start - 1; } /* * We still haven't the actual symbols, so guess the * last map final address. */ curr->end = ~0UL; I've noticed that if I change the symbol_conf.{use_modules,try_vmlinux_path} then I can get perf events for kernel symbols from /proc/kallsyms but nothing for the modules. Jamie