PPROF.md

Memory consumption testing with pprof

To use pprof to analyze performance and memory consumption in Envoy, you can use the built-in statically linked profiler, or dynamically link it in to a specific place yourself.

Linking

Static Linking

Static linking is already available (because of a HeapProfilerDump() call inside Envoy::Profiler::Heap::forceLink()).

Compiling a statically-linked Envoy

Build the static binary using bazel:

$ bazel build //source/exe:envoy-static

Running a statically-linked Envoy with pprof

And run the binary with a HEAPPROFILE environment variable, like so:

$ HEAPPROFILE=/tmp/mybin.hprof bazel-bin/source/exe/envoy-static <args>

HEAPPROFILE sets a location for the profiler output. A statically-linked binary must be run with this environment variable; a dynamically-linked binary will populate the working directory by default. (See Methodology.)

Dynamic Linking

Adding tcmalloc_dep to Envoy

A statically-linked Envoy will profile everything. In a dynamically-linked Envoy, you must add the HeapProfiler instructions yourself. HeapProfilerStart() will start recording allocations, HeapProfilerStop() will stop recording, and HeapProfilerDump() will dump an output to the specified directory. (See Gperftools Heap Profiler.)

To add a HeapProfiler breakpoint yourself, add tcmalloc as a dependency under the envoy_cc_library rule:

source/exe/BUILD

    envoy_cc_library(
       name = "envoy_common_lib",
+      tcmalloc_dep = 1,
       deps = [
       ...
    )

It is then necessary to add HeapProfilerStart() and HeapProfilerDump() breakpoints somewhere in Envoy. One place to start profiling is at the instantiation of MainCommonBase::MainCommonBase:

source/exe/main_common.cc

    // includes
    #include "gperftools/heap-profiler.h"
    ...
    MainCommonBase::MainCommonBase(...) : ... {
+       HeapProfilerStart("main_common_base"); // first line
        ...
    }

source/server/server.cc

    // includes
    #include "gperftools/heap-profiler.h"
    ...
    void InstanceImpl::Initialize(...) : ... {
        ...
+       HeapProfilerDump("main_common_base"); // last line
    }

Once these changes have been made in your working directory, it might make sense to save the diff as a patch (git diff > file), which can then be quickly applied/unapplied for testing and committing. (git apply, git apply -R)

Build the binary using bazel, and run the binary without any environment variables:

$ bazel build //source/exe:envoy
$ bazel-bin/source/exe/envoy <args>

This will dump your profiler output to the working directory.

Methodology

For consistent testing, it makes sense to run Envoy for a constant amount of time across trials:

$ timeout <num_seconds> bazel-bin/source/exe/envoy <options>

Envoy will print to stdout something like:

Starting tracking the heap

And then a series of stdouts like:

Dumping heap profile to <heap file 0001> (100 MB currently in use)
Dumping heap profile to <heap file 0002> (200 MB currently in use)
...

This will generate a series of files; if you statically-linked, these are wherever HEAPPROFILE points to. Otherwise, they are in the current directory by default. They'll be named something like main_common_base.0001.heap, main_common_base.0002.heap, etc.

NB: There is no reason this needs to be titled main_common_base. Whatever flag you supply HeapProfilerStart / HeapProfilerDump will become the filename. Multiple sections of code could be profiled simultaneously by setting multiple HeapProfilerStart() / HeapProfilerStop() breakpoints with unique identifiers.

Analyzing with pprof

pprof can read these heap files in a number of ways. Most convenient for first-order inspection might be pprof -top or pprof -text:

$ pprof -text bazel-bin/source/exe/envoy main_common_base* | head -n5
File: envoy
Build ID: ...
Type: inuse_space
Showing nodes accounting for 6402800.62kB, 98.59% of 6494044.58kB total
Dropped ... nodes (cum <= ...kB)

More complex flame/graph charts can be generated and viewed in a browser, which is often more helpful than text-based output:

$ pprof -http=localhost:9999 bazel-bin/source/exe/envoy main_common_base*