perf record always record the same kernel symbol

perf record always record the same kernel symbol

[Chao Xu]

Hi,

I issued the following commands:
sudo perf record sleep 1
sudo perf report

Here is a snippet from the output of perf report:
# Samples: 8  of event 'cycles'
# Event count (approx.): 1609581
#
# Overhead  Command      Shared Object  Symbol
# ........  .......  .................  ......
#
   100.00%    sleep  [kernel.kallsyms]  [k] 0xffffffff81043fea

I also tried to record other commands such as dd, ping, the symbol
showed in the output is always "[k] 0xffffffff81043fea", and this was
the only kernel symbol. I checked /proc/kallsyms, this symbol did not
exist in the file.

I built my kernel from linux source tree with the default config. I
tried on both 3.9.0 and 3.9.1. I built perf from
linux-source-tree/tools/perf with a simple "make".

Could someone suggest where did I go wrong? Thanks a bunch.
--
Regards,
Chao Xu

Re: perf record always record the same kernel symbol

[David Ahern]

On 5/10/13 1:04 PM, Chao Xu wrote:
> Hi,
>
> I issued the following commands:
> sudo perf record sleep 1
> sudo perf report

you are profiling the 'sleep' command which is not very exciting. Try:
   sudo perf record -a -- sleep 1
   sudo perf report

David

Re: perf record always record the same kernel symbol

[David Ahern]

On 5/10/13 1:58 PM, Chao Xu wrote:
> Thanks David. This indeed gave more samples. Do you know why the symbol
>   [k] 0xffffffff81043fea occured so often? As shown in the pasted
> result, both "swapper" and "perf" had this symbol. And if I "perf record
> dd if=/dev/zero of=/dev/null" or "perf record ping", they all showed
> this symbol. I pasted these results in the end of this email.
> I guess my real concern is the symbols cannot be mapped into meaningful
> function names. These symbols cannot be found in either /proc/kallsyms
> nor the vmlinux I built from the kernel source tree. Any idea? Thanks.

take a look at the output of report -v and report -D. For me those 
commands work just fine:

# perf record -a -- sleep 1
[ perf record: Woken up 1 times to write data ]
[ perf record: Captured and wrote 0.104 MB perf.data (~4527 samples) ]

# perf report

  38.39%       swapper  [kernel.kallsyms]   [k] intel_idle
   9.26%          perf  [kernel.kallsyms]   [k] generic_exec_single
   5.58%       swapper  [kernel.kallsyms]   [k] cpuidle_wrap_enter
   4.73%       swapper  [kernel.kallsyms]   [k] hpet_legacy_next_event
   4.47%       swapper  [kernel.kallsyms]   [k] _raw_spin_lock_irqsave
...

David

Re: perf record always record the same kernel symbol

[Chao Xu]

Thanks David. This indeed gave more samples. Do you know why the
symbol  [k] 0xffffffff81043fea occured so often? As shown in the
pasted result, both "swapper" and "perf" had this symbol. And if I
"perf record dd if=/dev/zero of=/dev/null" or "perf record ping", they
all showed this symbol. I pasted these results in the end of this
email.
I guess my real concern is the symbols cannot be mapped into
meaningful function names. These symbols cannot be found in either
/proc/kallsyms nor the vmlinux I built from the kernel source tree.
Any idea? Thanks.

result of sudo perf record -a -- sleep 1
# Samples: 104  of event 'cycles'
# Event count (approx.): 61197061

#
# Overhead          Command               Shared Object  Symbol
# ........  ...............  ..........................  ......
#
    47.49%          swapper  [kernel.kallsyms]           [k] 0xffffffff81043fea
    11.78%  chromium-browse  [kernel.kallsyms]           [k] 0xffffffff81095950
    11.46%  chromium-browse  chromium-browser            [.] 0x000000000160d0a6
     4.07%  chromium-browse  perf-5594.map               [.] 0x00000bb86b1cb70a
     4.07%             perf  [kernel.kallsyms]           [k] 0xffffffff81043fea
     2.38%            sleep  perf                        [.] 0x00000000000459da
     2.29%            sleep  [kernel.kallsyms]           [k] 0xffffffff813548c3
     2.05%             java  perf-3109.map               [.] 0x00007f84d5206071
     2.05%  indicator-cpufr  libgobject-2.0.so.0.3200.3  [.] 0x0000000000031787
     2.05%           compiz  libc-2.15.so                [.] 0x0000000000082fa6
     2.02%  chromium-browse  libflashplayer.so           [.] 0x0000000000803fe7
     1.88%             java  libglib-2.0.so.0.3200.3     [.] 0x0000000000045619
     1.72%  chromium-browse  libglib-2.0.so.0.3200.3     [.] 0x0000000000019930
     1.64%  chromium-browse  libpthread-2.15.so          [.] 0x000000000000cd60
     1.02%             Xorg  [kernel.kallsyms]           [k] 0xffffffff81044c1d
     0.62%          swapper  [i915]                      [k] 0x0000000000000ce5
     0.62%             Xorg  [i915]                      [k] 0x0000000000018a80
     0.51%             Xorg  Xorg                        [.] 0x000000000013a619
     0.29%      kworker/0:1  [kernel.kallsyms]           [k] 0xffffffff81096afc

result of sudo perf record dd if=/dev/zero of=/dev/null:
# Overhead  Command      Shared Object  Symbol
# ........  .......  .................  ......
#
    76.89%       dd  [kernel.kallsyms]  [k] 0xffffffff81043fea
    13.91%       dd  libc-2.15.so       [.] 0x000000000014815f
     9.21%       dd  dd                 [.] 0x0000000000004889

result of sudo perf record ping 10.0.0.1:
# Overhead  Command      Shared Object  Symbol
# ........  .......  .................  ......
#
    64.59%     ping  ld-2.15.so         [.] 0x00000000000188d2
    35.41%     ping  [kernel.kallsyms]  [k] 0xffffffff81043fea

--
Regards,
Chao Xu