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diff --git a/doc/dev/perf.rst b/doc/dev/perf.rst new file mode 100644 index 000000000..57742eec4 --- /dev/null +++ b/doc/dev/perf.rst @@ -0,0 +1,55 @@ +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 |