Chrome Version: 64
Chrome OS Version: 10042.0.0
Chrome OS Platform: multiple

perf is broken on CrOS 10042+, on multiple boards and kernel versions.
For detection context, see b/68045463.

I confirmed the issue on a lars board with kernel 3.18.

1) I installed image R64-10042.0.0.
While playing youtube in Chrome, I ran
$ perf record -a -e cycles -c 1000003 sleep 3
$ perf report -s dso
Warning:
Kernel address maps (/proc/{kallsyms,modules}) were restricted.

Check /proc/sys/kernel/kptr_restrict before running 'perf record'.

As no suitable kallsyms nor vmlinux was found, kernel samples
can't be resolved.

Samples in kernel modules can't be resolved as well.

# To display the perf.data header info, please use --header/--header-only
# options.
#
#
# Total Lost Samples: 0
#
# Samples: 1K of event 'cycles'
# Event count (approx.): 1239003717
#
# Overhead  Shared Object
# ........  ......................
#
    45.52%  [unknown]
    42.13%  chrome
     3.55%  libpthread-2.23.so
     2.10%  libc-2.23.so
     1.29%  i965_dri.so
     1.13%  perf-9261.map
     0.97%  i965_drv_video.so
     0.81%  libstdc++.so.6.0.20
     0.65%  [vdso]
     0.48%  cras
     0.40%  libEGL.so.1.0.0
     0.24%  libdrm_intel.so.1.0.0
     0.16%  libbase-core-395517.so
     0.16%  libcras.so.0.0.0
     0.08%  ld-2.23.so
     0.08%  libm-2.23.so
     0.08%  perf-4443.map
     0.08%  perf-4908.map
     0.08%  perf-5747.map

45.5% of samples associated with an unknown module.

2) I installed image R64-10041.0.0.
While playing youtube in Chrome, I ran
$ perf record -a -e cycles -c 1000003 sleep 3
$ perf report -s dso
# To display the perf.data header info, please use --header/--header-only
# options.
#
#
# Total Lost Samples: 0
#
# Samples: 1K of event 'cycles'
# Event count (approx.): 1805005415
#
# Overhead  Shared Object
# ........  .....................
#
    59.61%  chrome
    29.42%  [kernel.kallsyms]
     2.71%  libpthread-2.23.so
     1.88%  perf-3649.map
     1.77%  i965_dri.so
     1.50%  libc-2.23.so
     0.78%  i965_drv_video.so
     0.66%  libstdc++.so.6.0.20
     0.44%  perf-3921.map
     0.33%  libdrm_intel.so.1.0.0
     0.17%  [vdso]
     0.11%  libart.so
     0.11%  libm-2.23.so
     0.11%  libva.so.1.4000.0
     0.06%  libEGL.so.1.0.0
     0.06%  libGLESv2.so.2.0.0
     0.06%  libasound.so.2.0.0
     0.06%  libglapi.so.0.0.0
     0.06%  perf-3501.map
     0.06%  perf-3712.map
     0.06%  perf-4022.map

29.4% of the samples are mapped to the kernel. No unknown module.

Running perf report -D on the perf data files collected at (1) and (2) shows that for image 10042.0.0 there are no MMAP events for the kernel or any kernel modules.

For case (1), see also the warning: "Kernel address maps (/proc/{kallsyms,modules}) were restricted." printed when running perf report, so this seems to be related.

It looks like something has changed in 10042 that denies perf access to /proc/kallsyms and /proc/modules.


What is the impact to the user, and is there a workaround? If so, what is it?

This breaks go/cwp. We also just started releasing kernels compiled with AutoFDO profiles generated from CWP data. Not being able to collect perf data for the kernel will break that pipeline in a few weeks.

I am attaching the output of 'perf report -D | grep MMAP' for the two perf data files collected at (1) and (2).

 

Deleted: report_D_MMAP_10041.txt 1.0 MB

report_D_MMAP_10041.txt 1.0 MB View Download

Deleted: report_D_MMAP_10042.txt 917 KB

report_D_MMAP_10042.txt 917 KB View Download