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Re: [BUG REPORT] perf tools: x86_64: Broken calllchain when sampling taken at 'callq' instruction

From Ingo Molnar <mingo@kernel.org>
Newsgroups linux.kernel
Subject Re: [BUG REPORT] perf tools: x86_64: Broken calllchain when sampling taken at 'callq' instruction
Date 2015-11-19 11:30 +0100
Message-ID <qwuDv-820-5@gated-at.bofh.it> (permalink)
References (2 earlier) <qw6hQ-nn-15@gated-at.bofh.it> <qw6KS-Af-9@gated-at.bofh.it> <qw6KS-Af-7@gated-at.bofh.it> <qwr2V-5I2-5@gated-at.bofh.it> <qwrcB-5Lq-5@gated-at.bofh.it>
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* Wangnan (F) <wangnan0@huawei.com> wrote:

> 
> 
> On 2015/11/19 14:37, Ingo Molnar wrote:
> >* Wangnan (F) <wangnan0@huawei.com> wrote:
> >
> >>>perf cmdline is
> >>>
> >>># ./pref record  -g -F 9 --call-graph dwarf ./test_dwarf_unwind
> >>>
> >>>Use default events, precise_ip == 2 so uses PEBS.
> >>>
> >>Testetd 'cycles', 'cycles:p' and 'cycles:pp'. Only 'cycles:pp' captures
> >>sample at callq. So maybe a PEBS problem?
> >Well, that's how our PEBS sampling works: we roll back the instruction pointer to
> >point at the instruction generating the sample. The state itself is
> >post-instruction.
> 
> Just for curiosity:
> 
> how the interrupted process continue to execute, when the PC
> saved in pt_regs still pointed to 'callq' but SP and stack has
> already changes? Do we fix it in kernel, or by hardware?

PEBS is an asynchronous hardware tracing mechanism, when batched PEBS is used it 
might not even result in any interruption of execution. The 'pt_regs' does not 
necessarily correspond to an interrupted, restartable context - we take the RIP 
from the PEBS machinery and also use LBR and disassembly to determine the previous 
instruction, before reporting it to user-space.

Thanks,

	Ingo
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[BUG REPORT] perf tools: x86_64: Broken calllchain when sampling  taken at 'callq' instruction "Wangnan (F)" <wangnan0@huawei.com> - 2015-11-18 08:30 +0100
  Re: [BUG REPORT] perf tools: x86_64: Broken calllchain when sampling  taken at 'callq' instruction "Wangnan (F)" <wangnan0@huawei.com> - 2015-11-18 09:20 +0100
    Re: [BUG REPORT] perf tools: x86_64: Broken calllchain when sampling  taken at 'callq' instruction Ingo Molnar <mingo@kernel.org> - 2015-11-18 09:30 +0100
      Re: [BUG REPORT] perf tools: x86_64: Broken calllchain when sampling  taken at 'callq' instruction "Wangnan (F)" <wangnan0@huawei.com> - 2015-11-18 10:00 +0100
        Re: [BUG REPORT] perf tools: x86_64: Broken calllchain when sampling  taken at 'callq' instruction Ingo Molnar <mingo@kernel.org> - 2015-11-19 07:40 +0100
          Re: [BUG REPORT] perf tools: x86_64: Broken calllchain when sampling  taken at 'callq' instruction "Wangnan (F)" <wangnan0@huawei.com> - 2015-11-19 07:50 +0100
            Re: [BUG REPORT] perf tools: x86_64: Broken calllchain when sampling  taken at 'callq' instruction Ingo Molnar <mingo@kernel.org> - 2015-11-19 11:30 +0100
              Re: [BUG REPORT] perf tools: x86_64: Broken calllchain when sampling  taken at 'callq' instruction "Wangnan (F)" <wangnan0@huawei.com> - 2015-11-19 11:50 +0100
                Re: [BUG REPORT] perf tools: x86_64: Broken calllchain when sampling  taken at 'callq' instruction Peter Zijlstra <peterz@infradead.org> - 2015-11-19 12:30 +0100
              Re: [BUG REPORT] perf tools: x86_64: Broken calllchain when sampling  taken at 'callq' instruction Peter Zijlstra <peterz@infradead.org> - 2015-11-19 12:30 +0100
                Re: [BUG REPORT] perf tools: x86_64: Broken calllchain when sampling  taken at 'callq' instruction Ingo Molnar <mingo@kernel.org> - 2015-11-27 09:40 +0100
                Re: [BUG REPORT] perf tools: x86_64: Broken calllchain when sampling  taken at 'callq' instruction Peter Zijlstra <peterz@infradead.org> - 2015-11-30 10:30 +0100
      Re: [BUG REPORT] perf tools: x86_64: Broken calllchain when sampling  taken at 'callq' instruction "Wangnan (F)" <wangnan0@huawei.com> - 2015-11-18 10:10 +0100
  Re: [BUG REPORT] perf tools: x86_64: Broken calllchain when sampling  taken at 'callq' instruction Jiri Olsa <jolsa@redhat.com> - 2015-11-18 09:50 +0100
    Re: [BUG REPORT] perf tools: x86_64: Broken calllchain when sampling  taken at 'callq' instruction "Wangnan (F)" <wangnan0@huawei.com> - 2015-11-18 10:20 +0100

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