Using perf¶

Top:

sudo perf top -p `pidof ceph-osd`

To capture some data with call graphs:

sudo perf record -p `pidof ceph-osd` -F 99 --call-graph dwarf -- sleep 60

To view by caller (where you can see what each top function calls):

sudo perf report --call-graph caller

To view by callee (where you can see who calls each top function):

sudo perf report --call-graph callee

note: If the caller/callee views look the same you may be suffering from a kernel bug; upgrade to 4.8 or later.

Common Issues¶

Ceph use RelWithDebInfo as its default CMAKE_BUILD_TYPE. Hence -O2 -g is used to compile the tree in this case. And the -O2 optimization level enables -fomit-frame-pointer by default. But this prevents stack profilers from accessing the complete stack information. So one can disable this option when launching cmake

cmake -DCMAKE_CXX_FLAGS="-fno-omit-frame-pointer"

or when building the tree:

make CMAKE_CXX_FLAGS="-fno-omit-frame-pointer"

Flamegraphs¶

First, get things set up:

cd ~/src
git clone https://github.com/brendangregg/FlameGraph

Run ceph, then record some perf data:

sudo perf record -p `pidof ceph-osd` -F 99 --call-graph dwarf -- sleep 60

Then generate the flamegraph:

sudo perf script | ~/src/FlameGraph/stackcollapse-perf.pl > /tmp/folded
~/src/FlameGraph/flamegraph.pl /tmp/folded > /tmp/perf.svg
firefox /tmp/perf.svg