Converting Profiles for v5

lnt v5 convert-profile converts a profile into a profile document, the form in which a run submitted to an LNT v5 instance carries a test’s profile. So far, the only format it reads is that of Linux perf record.

Example

To convert bench.perf_data, the profile of the test bench:

lnt v5 convert-profile bench.perf_data > bench.profile.json

To get the profile document in the format a v5 run submission uses for a test’s profile (gzip-compressed, then base64-encoded), convert it with --encode:

lnt v5 convert-profile --encode bench.perf_data -o bench.profile

See lnt v5 convert-profile --help for the other options.

Function names

Each function is named by its demangled name, which c++filt (--cxxfilt) gives. A function listed under several names, such as an alias, or a symbol that is both static and dynamic, is listed only once.

A function is named by its mangled name instead when its demangled name is longer than 2048 bytes in UTF-8, or if its demangling collides with the name of another function. For example, a complete-object and a base-object constructor that are not aliases both demangle to A::A(). Since a profile only lists its hot functions, a demangled name can still stand for different functions in two profiles, if each lists only one of them.

The instructions’ text is whatever objdump produces.

What is left out

A v5 instance refuses a profile (and its run) that does not stay within its limits. The command therefore leaves out the functions that would be refused by the server on submission:

• a function whose name (even mangled) is longer than 2048 bytes;

• a function with more than 100,000 instructions;

• a function at an address larger than 2⁶³ - 1, e.g. the kernel’s.

The profile’s counters still include them. A profile that remains too large for an instance – more than 10,000 functions, or a document of more than 32 MiB, or 4 MiB compressed – is an error.