Messages in this thread | | | Date | Fri, 28 Jun 2013 17:09:51 -0700 | From | Sukadev Bhattiprolu <> | Subject | Re: [PATCH] perf: ARM: Record the user-mode PC in the call chain. |
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Will Deacon [will.deacon@arm.com] wrote: | On Thu, Jun 20, 2013 at 04:17:06AM +0100, Jed Davis wrote: | > On Tue, Jun 18, 2013 at 02:13:19PM +0100, Will Deacon wrote: | > > On Fri, Jun 14, 2013 at 12:21:11AM +0100, Jed Davis wrote: | > > > With this change, we no longer lose the innermost entry in the user-mode | > > > part of the call chain. See also the x86 port, which includes the ip. | > > > | > > > It's possible to partially work around this problem by post-processing | > > > the data to use the PERF_SAMPLE_IP value, but this works only if the CPU | > > > wasn't in the kernel when the sample was taken. | > > | > > Thanks. I guess we need something similar for arm64 too. Could you cook a | > > similar patch please? | > | > Done (and tested, on the ARM V8 Foundation Model). | | Wow, I didn't expect you to test it. Thanks! | | > It looked as if the powerpc and sparc ports might have similar issues, | > but I haven't checked on them yet. | | I can extract some hardware from the pile in the corner of my flat if you | want a hand with testing.
Interesting. Powerpc already saves the next_ip for the first entry:
arch/powerpc/perf/callchain.c:
perf_callchain_user_64(): ...
next_ip = perf_instruction_pointer(regs); lr = regs->link; sp = regs->gpr[1]; perf_callchain_store(entry, next_ip);
for (;;) {
Do you have a test case/output that I can run on Power ?
We actually have the opposite problem where we see duplication in callchains like this. We considered not saving the "link register" but that seems to break for a "leaf-node" functions.
13.65% sprintft libc-2.12.so [.] __random | --- __random | |--62.82%-- __random | | | |--97.31%-- rand | | do_my_sprintf | | main | | generic_start_main | | __libc_start_main | | 0x0 | | | --2.69%-- do_my_sprintf | main | generic_start_main | __libc_start_main | 0x0 | --37.18%-- rand | |--93.30%-- rand | do_my_sprintf | main | generic_start_main | __libc_start_main | 0x0 | --6.70%-- do_my_sprintf main generic_start_main __libc_start_main 0x0
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