linux-kernel - Re: [PATCH] perf: libdw support for powerpc

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Message-ID: <be48f6fe-0f0e-8667-0ad0-65e00904f008@redhat.com>
Date:   Thu, 18 May 2017 20:48:55 +0200
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     "Naveen N. Rao" <naveen.n.rao@...ux.vnet.ibm.com>,
        kvm@...r.kernel.org, linux-kernel@...r.kernel.org
Cc:     acme@...nel.org, Ravi Bangoria <ravi.bangoria@...ux.vnet.ibm.com>,
        linuxppc-dev@...ts.ozlabs.org
Subject: Re: [PATCH] perf: libdw support for powerpc



On 18/05/2017 20:19, Naveen N. Rao wrote:
> Paolo Bonzini wrote:
>> The ARM and x86 architectures already use libdw, and it is useful to
>> have as much common code for the unwinder as possible.  Porting PPC
>> to libdw only needs an architecture-specific hook to move the register
>> state from perf to libdw.
> 
> Thanks. Ravi has had a similar patch locally, but from what I
> understand, there are issues with libdw based unwinding on powerpc64. I
> gave this a quick test and I don't see the user-space call trace being
> unwinded properly with libdw.

I don't see that problem:

-   99,98%     0,00%  dd       libc-2.17.so                    [.] generic_start_main.isra.0
     generic_start_main.isra.0
   - main
      - 99,97% iread
         - 97,82% sys_read
            - 96,97% extract_entropy_user
                 89,44% powernv_get_random_long
                 4,63% sha_transform
                 2,07% extract_buf
           1,15% _raw_spin_lock_irqsave
           0,51% extract_buf

(This is "perf record dd if=/dev/urandom of=/dev/null bs=512").

Can you copy the contents of tools/perf/.config-detected here?

>> diff --git a/tools/perf/arch/powerpc/util/unwind-libdw.c
>> b/tools/perf/arch/powerpc/util/unwind-libdw.c
>> new file mode 100644
>> index 0000000..c61e1d8
>> --- /dev/null
>> +++ b/tools/perf/arch/powerpc/util/unwind-libdw.c
>> @@ -0,0 +1,73 @@
>> +#include <elfutils/libdwfl.h>
>> +#include "../../util/util.h"
>> +#include "../../util/unwind-libdw.h"
>> +#include "../../util/perf_regs.h"
> 
> As an aside, we also need to include "event.h", without which there are
> a few compile errors.

Oops, I was compiling this on 4.11.  Sorry.

Paolo