The changes in V4 can be found in each patch.
The basic usages of performance testing are,
$ make check-perf
$ make check-perf RUNTESTFLAGS="--target_board=native-gdbserver solib.exp"
$ make check-perf RUNTESTFLAGS="solib.exp SOLIB_COUNT=512"
We can skip compilation step like,
$ make check-perf RUNTESTFLAGS='solib.exp GDB_PERFTEST_MODE=run'
or only compile test cases,
$ make check-perf RUNTESTFLAGS='solib.exp GDB_PERFTEST_MODE=compile'
in default, GDB_PERFTEST_MODE=both.
If the perf test case takes much time, we can specify timeout by
GDB_PERFTEST_TIMEOUT=1000.
$ make check-perf RUNTESTFLAGS="--target_board=native-gdbserver GDB_PERFTEST_TIMEOUT=4000 solib.exp"